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Все живые организмы на Земле делятся на части, называемые ячейками. Есть более мелкие куски в клетки, которые включают белков и органелл. Есть также большие куски называется тканей и систем. Клетки малых отделений, которые держат все биологического оборудования, необходимого для позволяли организму выжить и успешно на Земле.
Основная цель ячейки организовать. Клетки провести различные части и каждая ячейка имеет свой набор функций. Это легче для организма, чтобы расти и выжить, когда клетки присутствуют. Если бы вы были только из одной ячейки, вы бы только быть в состоянии вырасти до определенного размера. Вы не можете найти отдельные клетки, которые являются как большие, как корова. Кроме того, если вы только одну ячейку вы не могли бы нервной системы, мышц не для движения, и использование Интернета будет и речи. Триллионов клеток в организме сделать вашу жизнь возможна.
Одно имя, много типов
Есть много типов клеток. В биологии класса, вы, как правило, работают с завода-подобных клеток и животных, как клетки. Будем говорить, животных, как, поскольку животное типа клеток может быть что угодно от крошечных микроорганизмов до нервных клеток в мозге. Растительные клетки легче определить, потому что они имеют защитное сооружение называется клеточной стенки изготовлены из целлюлозы. Растения имеют стены; животных нет. Растения также имеют органеллы, как хлоропластов (вещи, которые делают их зеленый) или больших заполненных водой вакуолей.
Мы сказали, что Есть много типов клеток. Клетки являются уникальными для каждого типа организма. Люди могут иметь сотни типов клеток. Некоторые клетки используются для перевозки кислорода (O2) через кровь (эритроциты) и другие могут быть специфическими для сердца. Если вы посмотрите на очень простых организмов, вы откроете для себя клетки, которые не определены ядра (прокариоты) и другие клетки, которые имеют сотни ядер (многоядерные). Что они все имеют в общем то, что они являются отделениями в окружении одних типов мембран.
وتنقسم جميع الكائنات الحية على الأرض في قطعة تسمى خلايا. وهناك قطع صغيرة إلى الخلايا التي تشمل البروتينات والعضيات. وهناك أيضا أكبر قطعة تسمى الأنسجة والأنظمة. الخلايا المقصورات الصغيرة التي تحمل جميع المعدات البيولوجية اللازمة للحفاظ على الكائن الحي على قيد الحياة وناجحة على الأرض.
والغرض الرئيسي من خلية في تنظيم. خلايا عقد مجموعة متنوعة من القطع وكل خلية لها مجموعة مختلفة من الوظائف. فمن الأسهل لكائن حي ينمو والبقاء على قيد الحياة عندما خلايا موجودة. إذا قدمت لك فقط من خلية واحدة ، هل ستكون قادرة على النمو فقط لحجم معين. كنت لا تجد الخلايا التي هي واحدة كبيرة مثل بقرة. أيضا ، إذا كانت خلية واحدة فقط يمكن أن لا يكون لديك الجهاز العصبي ، وليس لحركة العضلات ، واستخدام الإنترنت سيكون غير وارد. التريليونات من الخلايا في الجسم تجعل حياتك ممكن.
اسم واحد ، أنواع عديدة
هناك العديد من أنواع الخلايا. في فئة البيولوجيا ، سوف تعمل عادة مع الخلايا النباتية والخلايا الحيوانية مثل مثل. نقول مثل الحيوانات بسبب نوع من خلايا الحيوان ويمكن أن يكون أي شيء من الكائنات الحية الدقيقة صغيرة إلى الخلايا العصبية في الدماغ. الخلايا النباتية هي أسهل لتحديد لأن لديهم بنية حماية يسمى جدار الخلية المصنوعة من السليلوز. النباتات لها الجدار ؛ الحيوانات لا تفعل ذلك. النباتات كما العضيات مثل بلاستيدات الخضراء (الأشياء التي جعلها الأخضر) أو فجوات كبيرة مملوءة بالماء.
قلنا أن هناك العديد من أنواع الخلايا. الخلايا هي فريدة من نوعها على كل نوع من الكائنات الحية. قد البشر لديها المئات من أنواع الخلايا. وتستخدم بعض الخلايا على حمل الأكسجين (O2) وعن طريق الدم (خلايا الدم الحمراء) وغيرها قد تكون محددة للقلب. اذا نظرتم الى كائنات بسيطة جدا ، وسوف تكتشف الخلايا التي ليس لها نواة محددة (بدائيات النوى) والخلايا الأخرى التي لديها مئات النوى (متعددة النوى). الشيء لهم جميعا في مشتركة هي أنها محاطة مقصورات نوع من الغشاء.
पृथ्वी पर रहने वाले जीवों की सभी कोशिकाओं बुलाया टुकड़ों में विभाजित हैं. वहाँ कोशिकाओं है कि प्रोटीन और organelles शामिल करने के लिए छोटे टुकड़े कर रहे हैं. वहाँ भी बड़े टुकड़े ऊतकों और सिस्टम कहा जाता है. कोशिकाओं छोटे डिब्बों कि जैविक एक जीव जीवित है और पृथ्वी पर सफल रखने के लिए आवश्यक उपकरणों के सभी पकड़ रहे हैं.
किसी कक्ष का एक मुख्य उद्देश्य के लिए आयोजित है. कोशिकाओं के टुकड़े की एक किस्म पकड़ और प्रत्येक कक्ष कार्यों का एक अलग सेट है. यह आसान है एक जीव और विकास के लिए जीवित कोशिकाओं जब मौजूद हैं. यदि आप केवल एक कोशिका से बना रहे थे, आप केवल एक निश्चित आकार को विकसित करने में सक्षम हो जाएगा. आप एकल कक्षों के रूप में एक गाय के रूप में बड़े हो नहीं मिल रहा है. इसके अलावा, यदि आप केवल एक ही कक्ष थे आप एक तंत्रिका तंत्र, आंदोलन के लिए कोई मांसपेशियों, और इंटरनेट का उपयोग करते हुए सवाल से बाहर किया जाएगा नहीं हो सकता था. आपके शरीर में कोशिकाओं के अरबों अपने जीवन संभव बनाते हैं.
एक नाम, कई प्रकार
वहाँ की कोशिकाओं के कई प्रकार हैं. जीव विज्ञान वर्ग में, आप आमतौर पर पौधे की तरह कोशिकाओं और जानवर की तरह कोशिकाओं के साथ काम करेंगे. हम जानवर की तरह कहते हैं क्योंकि सेल का एक जानवर प्रकार एक छोटे सूक्ष्मजीव से आपके दिमाग में एक तंत्रिका कोशिका के लिए कुछ भी हो सकता है. संयंत्र कोशिकाओं की पहचान करने के लिए आसान है क्योंकि वे एक सुरक्षात्मक संरचना एक सेल सेलूलोज़ का बनाया दीवार कहा जाता है. पौधों की दीवार है, न जानवर. पौधों को भी chloroplast तरह organelles (चीजें हैं जो उन्हें हरा बनाने के लिए) या बड़े पानी से भरे vacuoles है.
हम ने कहा कि वहाँ की कोशिकाओं के कई प्रकार हैं. जीव की कोशिकाओं के प्रत्येक प्रकार के लिए अद्वितीय हैं. मानव कोशिकाओं के प्रकार के सैकड़ों हो सकता है. कुछ कक्षों में (लाल रक्त कोशिकाओं) खून और दूसरों के माध्यम से ऑक्सीजन (O2) ले जाने के लिए दिल के लिए विशेष हो सकता है किया जाता है. यदि आप बहुत साधारण जीवों पर देखो, तुम कोशिकाओं है कि कोई परिभाषित (prokaryotes) नाभिक और अन्य कोशिकाओं कि नाभिक के सैकड़ों किया है की खोज करेंगे (multinucleated). बात वे सभी आम में है कि वे झिल्ली के कुछ प्रकार से घिरा हुआ डिब्बों हैं.
Hindi | Arabic | Russian
All living organisms on Earth are divided in pieces called cells. There are smaller pieces to cells that include proteins and organelles. There are also larger pieces called tissues and systems. Cells are small compartments that hold all of the biological equipment necessary to keep an organism alive and successful on Earth.
A main purpose of a cell is to organize. Cells hold a variety of pieces and each cell has a different set of functions. It is easier for an organism to grow and survive when cells are present. If you were only made of one cell, you would only be able to grow to a certain size. You don't find single cells that are as large as a cow. Also, if you were only one cell you couldn't have a nervous system, no muscles for movement, and using the internet would be out of the question. The trillions of cells in your body make your life possible.
One Name, Many Types
There are many types of cells. In biology class, you will usually work with plant-like cells and animal-like cells. We say animal-like because an animal type of cell could be anything from a tiny microorganism to a nerve cell in your brain. Plant cells are easier to identify because they have a protective structure called a cell wall made of cellulose. Plants have the wall; animals do not. Plants also have organelles like the chloroplast (the things that make them green) or large water-filled vacuoles.
We said that there are many types of cells. Cells are unique to each type of organism. Humans may have hundreds of types of cells. Some cells are used to carry oxygen (O2) through the blood (red blood cells) and others might be specific to the heart. If you look at very simple organisms, you will discover cells that have no defined nucleus (prokaryotes) and other cells that have hundreds of nuclei (multinucleated). The thing they all have in common is that they are compartments surrounded by some type of membrane.
Hindi | Arabic | Russian
С появлением сетей быстрого питания, и все возрастающих темпов нашего образа жизни, он фактически был очень удобно заказать еду пойти на любые быстрого питания.
Помимо того, что они служат пищей, которая готовится всего несколько минут, они также дешевые и очень доступные. Это то, что стало с тех прекрасных сценариев столовая, который из-за постоянно меняющегося образа жизни человека уже считаются устаревшими.
Тем не менее, несмотря на эти преимущества, которые можно увидеть на обилие сетей быстрого питания, одна школа мысли особенно придерживаясь диетолог состояние исследований, которые блюд, которые подавались в быстром центров питания фактически лишены питания. Это может фактически привести к болезням, которые будут иметь пагубные последствия для здоровья организма.
Это мышление может быть заземлен с тем, что почти все, если не все, блюд, подаваемых в ресторанах быстрого питания сохраняются, и заранее приготовленные. Это причина, почему они действительно готовы после очень короткий промежуток времени. Кроме того, это причина, почему эти продукты питания являются на самом деле уязвимы к загрязнению из-за сохранения формулы используются для держать ее современном состоянии.
Продукты загрязненных продуктов питания стали растущую озабоченность с увеличением сети быстрого питания. С стремительно обслуживания и приготовления пищи доступных продуктов питания в сети быстрого питания, что, как правило, жертвуют является оздоровление бизнеса учреждение.
Хотя за продуктами и лекарствами фактически введенные правила, касающиеся санитарных ресторанов и розничной торговли продовольствием и продолжается регулирование же в течение всего года, факт остается фактом, что загрязненные продукты питания был обильным в частности, в сети быстрого питания.
Пищевое отравление было рассматривать как один из наиболее многочисленных источников личных претензий травмы. Обычно это вызвано небрежностью в приготовлении пищи, ведущих к загрязненных пищевых продуктов.
Пищевое отравление может проявляться в различных формах в том числе: рвота, спазмы в животе и диарея. Эти травмы Между тем может привести к серьезным последствиям, таким как обезвоживание, головные боли, и даже фатальным результатам, как смерть.
Личные претензии травмы вызванные травмами опытных от пищевого отравления рассматривается как одна из самых страшных опыта можно когда-либо сталкиваться. Вместо того, чтобы питательные тела с питанием, что пища может принести, он может фактически привести к распаду тела из-сказал приема пищи.
مع ظهور سلاسل الوجبات السريعة ، وتيرة متزايدة من أسلوب حياتنا ، فقد كان في الواقع كثيرا جدا مريحة للنظام الغذائي للذهاب في أي مؤسسات الوجبات السريعة.
وبصرف النظر عن حقيقة أنها تخدم المواد الغذائية التي يتم طهيها في الأمر مجرد دقائق ، كما أنها رخيصة جدا ويمكن الوصول إليها من ذلك بكثير. هذا هو ما أصبح من هذه السيناريوهات غرامة الطعام ، بسبب نمط الحياة الذي الرجل المتغيرة باستمرار وقد تم بالفعل تعتبر قديمة.
لكن على الرغم من هذه المزايا التي يمكن أن ينظر إليها على وفرة من سلاسل الوجبات السريعة ، ويعتقد واحد من المدرسة ولا سيما تلك الدولة الانضمام إلى دراسات التغذية أن الأطعمة خدم في مراكز الوجبات السريعة خاوية في الواقع من التغذية. قد يكون في الواقع أيضا أن تؤدي إلى الأمراض التي من شأنها أن تكون ضارة على صحة الجسم.
قد يكون أساس هذا التفكير من حقيقة أن معظم ، إن لم يكن كل شيء ، الطعام الذي يقدم في مطاعم الوجبات السريعة والحفاظ عليها ، وقبل طهيها. هذا هو السبب في انهم مستعدون فعلا بعد فترة قصيرة جدا من الزمن. هذا أيضا هو السبب الذي يجعل هذه المنتجات الغذائية عرضة للتلوث في الواقع بسبب الحفاظ على الصيغة المستخدمة للحفاظ على حالتها الراهنة.
أصبحت المنتجات الغذائية الملوثة مصدر قلق متزايد مع زيادة سلاسل الوجبات السريعة. مع سرعة وتيرة خدمة والطبخ من المنتجات الغذائية المتوفرة في سلاسل الوجبات السريعة ، ما هو التضحية عادة هو الصرف الصحي لإنشاء الأعمال التجارية.
على الرغم من أن إدارة الغذاء والدواء وفرضت فعلا القواعد المتعلقة الصرف الصحي من المطاعم ومحلات التجزئة للمواد الغذائية واستمرار تنظيم نفسها على مدار العام كله ، تظل الحقيقة أن الأغذية الملوثة وقد وفيرة ولا سيما في مطاعم الوجبات السريعة.
وقد نظرت التسمم الغذائي باعتبارها واحدة من مصدر أكثر عددا من المطالبات من الإصابات الشخصية. عادة يتم إحضارها عن هذا الاهمال من قبل في إعداد الطعام مما يؤدي إلى المنتجات الغذائية الملوثة.
قد يكون التسمم الغذائي يتجلى في أشكال عدة تشمل ما يلي : القيء ، وتشنجات في المعدة ، والإسهال. هذه الإصابات قد تؤدي في الوقت نفسه لعواقب وخيمة مثل الجفاف ، والصداع ، والنتائج حتى فادح كما الموت.
وتعتبر الإصابة الشخصية المطالبات الناجمة عن الإصابات من ذوي الخبرة من التسمم الغذائي باعتبارها واحدة من أكثر التجارب اللعين واحدة قد تصادف أي وقت مضى. بدلا من تغذية الجسم مع التغذية أن الطعام قد يؤدي ، في الواقع قد يؤدي إلى اضمحلال الجسم بسبب تناول الطعام قال.
फास्ट फूड चेन के आगमन, और हमारे जीवन शैली की बढ़ती रफ्तार के साथ, यह वास्तव में बहुत ज्यादा करने के लिए किसी भी तेजी से खाद्य प्रतिष्ठानों पर जाने के भोजन का आदेश सुविधाजनक हो गया है.
तथ्य यह है कि वे खाना है कि मिनट का सिर्फ एक मामले में पकाया जाता है की सेवा के अलावा, वे भी सस्ते और बहुत से उपलब्ध हैं. यह वही है जो उन परिदृश्यों को ठीक भोजन, जो आदमी कभी बदलती जीवन शैली की वजह से पहले से ही अप्रचलित रूप में हुआ है बन गया है.
इन लाभ है कि फास्ट फूड चेन की बहुतायत पर देखा जा सकता है बावजूद फिर भी, एक का स्कूल विशेष रूप से उन का पालन पोषण पढ़ाई राज्य के लिए सोचा है कि फास्ट फूड केंद्रों में कार्य खाद्य पदार्थ वास्तव में पोषण से रहित हैं. यह वास्तव में भी रोग है कि शरीर के स्वास्थ्य के लिए हानिकारक हो जाएगा करने के लिए नेतृत्व कर सकते हैं.
इस सोच से तथ्य है कि लगभग सभी आधारित हो सकता है, नहीं तो सब, फास्ट फूड रेस्तरां में परोसा भोजन कर रहे हैं संरक्षित है, और पूर्व पकाया. यह कारण है कि वे वास्तव में समय की एक बहुत ही कम समय के बाद तैयार हो रहा है. इसके अलावा इस कारण है कि इन खाद्य उत्पादों वास्तव में संरक्षण के लिए अपनी वर्तमान स्थिति रखने के लिए उपयोग किया सूत्र की वजह से प्रदूषण की चपेट में हैं.
दूषित खाद्य उत्पादों फास्ट फूड चेन की वृद्धि के साथ एक बढ़ती चिंता का विषय बन गए हैं. साथ तेजी से सेवारत और फास्ट फूड चेन है, जो आमतौर पर बलिदान है में उपलब्ध खाद्य उत्पादों की खाना पकाने से पुस्तक व्यावसायिक प्रतिष्ठान की सफाई है.
हालांकि खाद्य एवं औषधि प्रशासन वास्तव में रेस्तरां और खुदरा खाद्य दुकानों और पूरे साल भर में ही की सतत विनियमन की स्वच्छता के संबंध में नियम लागू किया गया है, इस तथ्य यह है कि दूषित भोजन फास्ट फूड चेन में विशेष रूप से प्रचुर मात्रा में किया गया है.
विषाक्त भोजन एक व्यक्तिगत चोट के दावों की अधिक अनेक स्रोत के रूप में माना गया है. यह आमतौर पर भोजन तैयार करने में लापरवाही दूषित खाद्य उत्पादों के लिए अग्रणी द्वारा होता है के बारे में लाया.
उल्टी, पेट में ऐंठन और दस्त: खाद्य विषाक्तता के लिए कई रूपों में प्रकट शामिल हो सकता है. इन चोटों बीच निर्जलीकरण, सिर दर्द जैसे कठोर परिणाम, और मौत के रूप में घातक रूप में भी परिणाम के लिए नेतृत्व कर सकते हैं.
व्यक्तिगत चोट विषाक्त भोजन से अनुभवी चोटों के बारे में द्वारा लाया का दावा सबसे खूंखार अनुभव भी कभी मुठभेड़ हो सकता है के रूप में माना जाता है. पोषण है कि एक खाना लाने सकता है के साथ शरीर पौष्टिक के बजाय, यह वास्तव में शरीर का क्षय करने के लिए परिणाम की वजह से भोजन का सेवन कहा हो सकता है.
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With the advent of fast food chains, and the ever-increasing pace of our lifestyle, it has actually been very much convenient to order food to go on any fast food establishments.
Aside from the fact that they serve food that is cooked in just matter of minutes, they are also cheap and very much accessible. This is what has become of those fine dining scenarios, which because of man's ever-changing lifestyle has already been considered as obsolete.
Yet despite these advantages that may be seen on the abundance of fast food chains, one school of thought particularly those adhering to nutritionist studies state that foods served in fast food centers are actually devoid of nutrition. It may actually also lead to diseases that would be detrimental to the body's health.
This thinking may be grounded from the fact that almost all, if not all, food served in fast food restaurants are preserved, and pre-cooked. This is the reason why they are actually ready after a very short span of time. Also this is the reason why these food products are actually vulnerable to contamination because of the preservation formula utilized to keep its present state.
Contaminated food products have become a growing concern with the increase of fast food chains. With the fast-paced serving and cooking of available food products in fast food chains, what is usually sacrificed is the sanitation of the business establishment.
Although the Food and Drug Administration has actually imposed rules regarding the sanitation of restaurants and retail food outlets and the continuing regulation of the same throughout the entire year, the fact remains that contaminated food has been abundant particularly in fast food chains.
Food poisoning has been considered as one of the more numerous source of personal injury claims. This is usually brought about by the negligence in food preparation leading to contaminated food products.
Food poisoning may be manifested in several forms to include: vomiting, stomach cramps, and diarrhea. These injuries meanwhile may lead to drastic consequences such as dehydration, headaches, and even results as fatal as death.
Personal injury claims brought about by injuries experienced from food poisoning is considered as one of the most dreaded experiences one may ever encounter. Instead of nourishing the body with the nutrition that a food may bring, it may actually result to the decay of the body because of the said food intake.
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Although we cannot see black holes, we can detect or guess the presence of one by measuring its effects on objects around it. The following effects may be used:
* Mass estimates from objects orbiting a black hole or spiraling into the core
* Gravitational lens effects
* Emitted radiation
Many black holes have objects around them, and by looking at the behavior of the objects you can detect the presence of a black hole. You then use measurements of the movement of objects around a suspected black hole to calculate the black hole's mass.
What you look for is a star or a disk of gas that is behaving as though there were a large mass nearby. For example, if a visible star or disk of gas has a "wobbling" motion or spinning AND there is not a visible reason for this motion AND the invisible reason has an effect that appears to be caused by an object with a mass greater than three solar masses (too big to be a neutron star), then it is possible that a black hole is causing the motion. You then estimate the mass of the black hole by looking at the effect it has on the visible object.
For example, in the core of galaxy NGC 4261, there is a brown, spiral-shaped disk that is rotating. The disk is about the size of our solar system, but weighs 1.2 billion times as much as the sun. Such a huge mass for a disk might indicate that a black hole is present within the disk.
Einstein's General Theory of Relativity predicted that gravity could bend space. This was later confirmed during a solar eclipse when a star's position was measured before, during and after the eclipse. The star's position shifted because the light from the star was bent by the sun's gravity. Therefore, an object with immense gravity (like a galaxy or black hole) between the Earth and a distant object could bend the light from the distant object into a focus, much like a lens can. This effect can be seen in the image below.
In the above image, the brightening of MACHO-96-BL5 happened when a gravitational lens passed between it and the Earth. When the Hubble Space Telescope looked at the object, it saw two images of the object close together, which indicated a gravitational lens effect. The intervening object was unseen. Therefore, it was concluded that a black hole had passed between Earth and the object.
When material falls into a black hole from a companion star, it gets heated to millions of degrees Kelvin and accelerated. The superheated materials emit X-rays, which can be detected by X-ray telescopes such as the orbiting Chandra X-ray Observatory.
The star Cygnus X-1 is a strong X-ray source and is considered to be a good candidate for a black hole. As pictured above, stellar winds from the companion star, HDE 226868, blow material onto the accretion disk surrounding the black hole. As this material falls into the black hole, it emits X-rays, as seen in this image:
In addition to X-rays, black holes can also eject materials at high speeds to form jets. Many galaxies have been observed with such jets. Currently, it is thought that these galaxies have supermassive black holes (billions of solar masses) at their centers that produce the jets as well as strong radio emissions. One such example is the galaxy M87 as shown below:
t is important to remember that black holes are not cosmic vacuum cleaners -- they will not consume everything. So although we cannot see black holes, there is indirect evidence that they exist. They have been associated with time travel and worm holes and remain fascinating objects in the universe.
History: The concept of an object from which light could not escape (e.g., black hole) was originally proposed by Pierre Simon Laplace in 1795. Using Newton's Theory of Gravity, Laplace calculated that if an object were compressed into a small enough radius, then the escape velocity of that object would be faster than the speed of light.
What Is A Black Hole ?
A black hole is what remains when a massive star dies.
If you have read How Stars Work, then you know that a star is a huge, amazing fusion reactor. Because stars are so massive and made out of gas, there is an intense gravitational field that is always trying to collapse the star. The fusion reactions happening in the core are like a giant fusion bomb that is trying to explode the star. The balance between the gravitational forces and the explosive forces is what defines the size of the star.
As the star dies, the nuclear fusion reactions stop because the fuel for these reactions gets burned up. At the same time, the star's gravity pulls material inward and compresses the core. As the core compresses, it heats up and eventually creates a supernova explosion in which the material and radiation blasts out into space. What remains is the highly compressed, and extremely massive,
core. The core's gravity is so strong that even light cannot escape.
This object is now a black hole and literally disappears from view. Because the core's gravity is so strong, the core sinks through the fabric of space-time, creating a hole in space-time -- this is why the object is called a black hole.
The core becomes the central part of the black hole called the singularity. The opening of the hole is called the event horizon.
You can think of the event horizon as the mouth of the black hole. Once something passes the event horizon, it is gone for good. Once inside the event horizon, all "events" (points in space-time) stop, and nothing (even light) can escape. The radius of the event horizon is called the Schwarzschild radius, named after astronomer Karl Schwarzschild, whose work led to the theory of black holes.
Types of Black Holes
There are two types of black holes:
* Schwarzschild - Non-rotating black hole
* Kerr - Rotating black hole
The Schwarzschild black hole is the simplest black hole, in which the core does not rotate. This type of black hole only has a singularity and an event horizon.
The Kerr black hole, which is probably the most common form in nature, rotates because the star from which it was formed was rotating. When the rotating star collapses, the core continues to rotate, and this carried over to the black hole (conservation of angular momentum). The Kerr black hole has the following parts:
* Singularity - The collapsed core
* Event horizon - The opening of the hole
* Ergosphere - An egg-shaped region of distorted space around the event horizon (The distortion is caused by the spinning of the black hole, which "drags" the space around it.)
* Static limit - The boundary between the ergosphere and normal space
If an object passes into the ergosphere it can still be ejected from the black hole by gaining energy from the hole's rotation.
However, if an object crosses the event horizon, it will be sucked into the black hole and never escape. What happens inside the black hole is unknown; even our current theories of physics do not apply in the vicinity of a singularity.
Even though we cannot see a black hole, it does have three properties that can or could be measured:
* Electric charge
* Rate of rotation (angular momentum)
As of now, we can only measure the mass of the black hole reliably by the movement of other objects around it. If a black hole has a companion (another star or disk of material), it is possible to measure the radius of rotation or speed of orbit of the material around the unseen black hole. The mass of the black hole can be calculated using Kepler's Modified Third Law of Planetary Motion or rotational motion.
What is quantum mechanics?
Quantum mechanics is a relatively recent area of physics which studies the behaviour of the tiniest existing components of matter. Tiny they may be, but discoveries about these particles have turned our understanding of the world on its head.
One of the central characters in the film Watchmen is Dr Manhattan, a physicist turned superhero following an accident in his lab. Manhattan is able to teleport, see into the future and past, duplicate himself and much more. But what if the most superhuman of his powers was that of understanding quantum mechanics?
What makes quantum physics awkward to get to grips with is that in many ways the workings of particles at a subatomic scale contradict everyday logic. ‘We are in an area which is very difficult to imagine because it’s so different from the macroscopic world we live in,’ explains Vlatko Vedral, professor of quantum information science at Leeds University. ‘So it’s very difficult to relate everyday objects we know to the behaviour of small objects.’
For the most part, classical physics is intuitive: whether or not you are aware of Newton’s laws, when you kick a ball common sense and everyday experience allow you to make a pretty good estimate of where it will go.
But imagine for a second that your football began to behave like an electron. In that case, quantum physics would tell you that it's impossible to know where your ball will land, and, come to think of it, if you look at it from the right angle it is actually a wave of energy rather than a physical object.
From equations to reality
Things really begin to get hairy when you pause to consider the wider implications of quantum mechanics. As everything around us is made up of these tiny constituents, how does their odd behaviour impact upon reality as we know it?
‘For all that we know, every quantum object - a particle of light, a particle of matter like an atom even a small molecule - can simultaneously exist in different places at the same time,’ says Vedral. How such properties might translate into the reality we perceive with our human senses remains a mystery.
As a result, there is fiery debate amongst physicists on how to reconcile quantum mechanics with what we see around us on a day to day basis. ‘I would say most of us certainly agree up to a certain level what the predictions are, but as you scale it up then you really have a strong division in the community,’ comments Vedral.
‘We have something spectacularly successful when it comes to predictions, but somehow we find it very difficult to understand what these actually mean,’ he adds.
Philosophical musings aside, the fact remains that at a subatomic level, quantum mechanics just works, even if it sometimes seems to defy the human imagination.
Vedral takes the example of the structure of an atom: ‘For me it’s very difficult to tell you what an atom really is, because it’s now outside our visualisation - it’s difficult to draw it, to come up with a geometric image. But I can still use the correct mathematics to make predictions about what will happen if you move it, or shine a laser on it.’
This means that practical applications of quantum mechanics such as quantum computing or cryptography are likely to see the light of the day in the near future, even if gaining a complete understanding of quantum mechanics remains a distant dream.
Researchers surveyed smokers intentions to quit after viewing four cigarette packages, including one with a warning label only and three with photographs of the negative consequences of smoking. (Credit: Image courtesy of University of Arkansas, Fayetteville)
Marketing researchers at the University of Arkansas, Villanova University and Marquette University surveyed more than 500 U.S. and Canadian smokers and found that the highly graphic images of the negative consequences of smoking have the greatest impact on smokers' intentions to quit. The most graphic images, such as those showing severe mouth diseases, including disfigured, blackened and cancerous tissue, evoked fear about the consequences of smoking and thus influenced consumer intentions to quit.
"These results suggest that there appears to be little downside on intentions to quit from using extremely graphic pictorial depictions of the negative health outcomes due to smoking," said Scot Burton, co-author of the study and marketing professor in the Sam M. Walton College of Business. "Our research shows that strong, negative graphic imagery -- and fear evoked from such imagery -- influences smokers' intentions to quit. We also found this to be the case even though recall of the written messages on package labels was reduced by the more graphic images. In other words, smokers were influenced primarily by the images and not by the written message."
Burton, Jeremy Kees and John Kozup, both marketing professors at the Villanova University, and Craig Andrews, marketing professor at Marquette University, developed the study to help officials at the U.S. Food and Drug Administration and the U.S. Department of Health and Human Services better understand what types of pictorial warnings are most effective and why they are effective. These agencies are responsible for implementing the 2009 Family Smoking Prevention and Tobacco Control Act, which requires graphic pictorial warning labels on cigarette packages by 2011. According to the law, "color graphics depicting the negative health consequences of smoking" must accompany cigarette package message statements, such as "Smoking Causes Mouth Diseases."
To mostly positive effects, Canada, Australia and many European countries already use strong written messages and graphic images on cigarette packages. The new U.S. law will align messages and pictorial warnings more closely with those on cigarette packages in these countries.
Smoking causes many health problems, from emphysema and lung cancer to a variety of cardiovascular diseases. For this study, the researchers chose its effect on oral diseases, the most externally visible health consequence. They started by using images that ranged from highly graphic -- vivid and powerful images of advanced mouth cancer -- to less graphic -- photographs of stained teeth caused by nicotine. In all, the graphic pictorial warnings were categorized as low, moderate or highly graphic.
In the primary study, 511 adult smokers, all members of a web-based research panel, were shown one of four different types of warning information on cigarette packages. These included one of the three photographs along with this written message: "WARNING: Smoking Causes Mouth Diseases." The fourth package included the written message with no picture. The warning information covered approximately 40 percent of the entire package. Participants were asked questions concerning their opinions about the cigarette package and intentions to quit smoking.
Participant responses indicated that pictorial warnings had a significantly positive effect on smokers' intentions to quit. Specifically, when compared to the moderate and low graphic levels, the highly graphic condition resulted in a significant increase in quit intentions. Moderate graphic levels also were associated with higher quit intentions than low graphic levels. Compared to the warning label with a written message only, the less graphic picture was not effective at strengthening smokers' intentions to quit.
The researchers found that participant recall of the written-message statement was reduced by the moderate and highly graphic pictorial warnings. Participants had greater recall of the written messages when they were packaged with "low" graphic pictorial warnings or with no image.
"However, it is worth noting here that recall of the stated warning is likely to be influenced by multiple exposures to the warnings," Kees said. "For instance, the graphic pictorial warnings may negatively affect recall initially because smokers are more 'shocked' by the warnings, but the stated message may be better remembered over time."
The researchers found that the graphic images evoked fear, which in turn served as the primary underlying mechanism explaining the effects of the pictorial warnings. As depictions of the consequences of smoking were presented more graphically, smokers reported higher levels of fear, Burton said. Also, the findings were consistent across variations in the amount of time participants were exposed to the packages, which suggested that even a relatively limited exposure to the warning label might achieve the desired effect to motivate smokers to quit.
"We believe our study provides some valuable implications for health policy," Burton said. "As public health officials and policy makers in the U.S. and around the world consider potential changes to warnings on cigarette packages, the addition of pictorial warnings, especially more graphic depictions of the consequences of smoking, to text-based messages appears beneficial. These data show that at least moderately graphic pictures should be used."
This composite image shows a supernova within the galaxy M100 that may contain the youngest known black hole in our cosmic neighborhood. In this image, Chandra's X-rays are colored gold, while optical data from ESO's Very Large Telescope are shown in red, green, and blue, and infrared data from Spitzer are red. The location of the supernova, known as SN 1979C, is labeled. (Credit: X-ray: NASA/CXC/SAO/D.Patnaude et al, Optical: ESO/VLT, Infrared: NASA/JPL/Caltech)
Astronomers using NASA's Chandra X-ray Observatory have found evidence of the youngest black hole known to exist in our cosmic neighborhood. The 30-year-old black hole provides a unique opportunity to watch this type of object develop from infancy.
The black hole could help scientists better understand how massive stars explode, which ones leave behind black holes or neutron stars, and the number of black holes in our galaxy and others.
The 30-year-old object is a remnant of SN 1979C, a supernova in the galaxy M100 approximately 50 million light years from Earth. Data from Chandra, NASA's Swift satellite, the European Space Agency's XMM-Newton and the German ROSAT observatory revealed a bright source of X-rays that has remained steady during observation from 1995 to 2007. This suggests the object is a black hole being fed either by material falling into it from the supernova or a binary companion.
"If our interpretation is correct, this is the nearest example where the birth of a black hole has been observed," said Daniel Patnaude of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. who led the study.
The scientists think SN 1979C, first discovered by an amateur astronomer in 1979, formed when a star about 20 times more massive than the sun collapsed. Many new black holes in the distant universe previously have been detected in the form of gamma-ray bursts (GRBs).
However, SN 1979C is different because it is much closer and belongs to a class of supernovas unlikely to be associated with a GRB. Theory predicts most black holes in the universe should form when the core of a star collapses and a GRB is not produced.
"This may be the first time the common way of making a black hole has been observed," said co-author Abraham Loeb, also of the Harvard-Smithsonian Center for Astrophysics. "However, it is very difficult to detect this type of black hole birth because decades of X-ray observations are needed to make the case."
The idea of a black hole with an observed age of only about 30 years is consistent with recent theoretical work. In 2005, a theory was presented that the bright optical light of this supernova was powered by a jet from a black hole that was unable to penetrate the hydrogen envelope of the star to form a GRB. The results seen in the observations of SN 1979C fit this theory very well.
Although the evidence points to a newly formed black hole in SN 1979C, another intriguing possibility is that a young, rapidly spinning neutron star with a powerful wind of high energy particles could be responsible for the X-ray emission. This would make the object in SN 1979C the youngest and brightest example of such a "pulsar wind nebula" and the youngest known neutron star. The Crab pulsar, the best-known example of a bright pulsar wind nebula, is about 950 years old.
"It's very rewarding to see how the commitment of some of the most advanced telescopes in space, like Chandra, can help complete the story," said Jon Morse, head of the Astrophysics Division at NASA's Science Mission Directorate.
The results will appear in the New Astronomy journal in a paper by Patnaude, Loeb, and Christine Jones of the Harvard-Smithsonian Center for Astrophysics. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge.
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Still image from movie displaying the computed horizons of large and small black holes immediately prior to their final merger and the aftermath. The oscillations induced by the small black hole falling into its companion are depicted. At the moment of merger, the large black hole’s radius increases with the absorption of the smaller mass. (Credit: Simulation by Carlos Lousto and Yosef Zlochower; visualization by Hans-Peter Bischof at the Center for Computational Relativity and Gravitation at Rochester Institute of Technology)
Scientists have simulated, for the first time, the merger of two black holes of vastly different sizes, with one mass 100 times larger than the other. This extreme mass ratio of 100:1 breaks a barrier in the fields of numerical relativity and gravitational wave astronomy.
Until now, the problem of simulating the merger of binary black holes with extreme size differences had remained an unexplored region of black-hole physics.
"Nature doesn't collide black holes of equal masses," says Carlos Lousto, associate professor of mathematical sciences at Rochester Institute of Technology and a member of the Center for Computational Relativity and Gravitation. "They have mass ratios of 1:3, 1:10, 1:100 or even 1:1 million. This puts us in a better situation for simulating realistic astrophysical scenarios and for predicting what observers should see and for telling them what to look for.
"Leaders in the field believed solving the 100:1 mass ratio problem would take five to 10 more years and significant advances in computational power. It was thought to be technically impossible."
"These simulations were made possible by advances both in the scaling and performance of relativity computer codes on thousands of processors, and advances in our understanding of how gauge conditions can be modified to self-adapt to the vastly different scales in the problem," adds Yosef Zlochower, assistant professor of mathematical sciences and a member of the center.
A paper announcing Lousto and Zlochower's findings was submitted for publication in Physical Review Letters.
The only prior simulation describing an extreme merger of black holes focused on a scenario involving a 1:10 mass ratio. Those techniques could not be expanded to a bigger scale, Lousto explained. To handle the larger mass ratios, he and Zlochower developed numerical and analytical techniques based on the moving puncture approach -- a breakthrough, created with Manuela Campanelli, director of the Center for Computational Relativity and Gravitation, that led to one of the first simulations of black holes on supercomputers in 2005.
The flexible techniques Lousto and Zlochower advanced for this scenario also translate to spinning binary black holes and for cases involving smaller mass ratios. These methods give the scientists ways to explore mass ratio limits and for modeling observational effects.
Lousto and Zlochower used resources at the Texas Advanced Computer Center, home to the Ranger supercomputer, to process the massive computations. The computer, which has 70,000 processors, took nearly three months to complete the simulation describing the most extreme-mass-ratio merger of black holes to date.
"Their work is pushing the limit of what we can do today," Campanelli says. "Now we have the tools to deal with a new system."
Simulations like Lousto and Zlochower's will help observational astronomers detect mergers of black holes with large size differentials using the future Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) and the space probe LISA (Laser Interferometer Space Antenna). Simulations of black-hole mergers provide blueprints or templates for observational scientists attempting to discern signatures of massive collisions. Observing and measuring gravitational waves created when black holes coalesce could confirm a key prediction of Einstein's general theory of relativity.
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The Risks of Waterborne Disease
It is easy to take for granted the safety of modern municipal drinking water, but prior to widespread filtration and chlorination, contaminated drinking water presented a significant public health risk. The microscopic waterborne agents of cholera, typhoid fever, dysentery and hepatitis A killed thousands of U.S. residents annually before disinfection methods were employed routinely, starting about a century ago. Although these pathogens are defeated regularly now by technologies such as chlorination, they should be thought of as ever-ready to “stage a come-back” given conditions of inadequate or no disinfection.
Illnesses Associated with Waterborne Pathogens
Worldwide, about 1.2 billion people lack access to safe drinking water, and twice that many lack adequate sanitation. As a result, the World Health Organization estimates that 3.4 million people, mostly children, die every year from water-related diseases (WHO, 2002a). In the U.S., outbreaks are commonly associated with contaminated groundwater which has not been properly disinfected. In addition, contamination of the distribution system can occur with water main breaks or other emergency situations (CDC, 2002).
Drinking water pathogens may be divided into three general categories: bacteria, viruses and parasitic protozoa. Bacteria and viruses contaminate both surface and groundwater, whereas parasitic protozoa appear predominantly in surface water. The purpose of disinfection is to kill or inactivate microorganisms so that they cannot reproduce and infect human hosts. Bacteria and viruses are well-controlled by normal chlorination, in contrast to parasitic protozoa, which demand more sophisticated control measures. For that reason, parasitic protozoan infections may be more common than bacterial or viral infections in areas where some degree of disinfection is achieved.
Bacteria are microorganisms often composed of single cells shaped like rods, spheres or spiral structures. Prior to widespread chlorination of drinking water, bacteria like Vibrio cholerae, Salmonella typhii and several species of Shigella routinely inflicted serious diseases such as cholera, typhoid fever and bacillary dysentery, respectively. As recently as 2000, a drinking water outbreak of E. coli in Walkerton, Ontario sickened 2,300 residents and killed seven when operators failed to properly disinfect the municipal water supply. While developed nations have largely conquered water-borne bacterial pathogens through the use of chlorine and other disinfectants, the developing world still grapples with these public health enemies.
Viruses are infectious agents that can reproduce only within living host cells. Shaped like rods, spheres or filaments, viruses are so small that they pass through filters that retain bacteria. Enteric viruses, such as hepatitis A, Norwalk virus and rotavirus are excreted in the feces of infected individuals and may contaminate water intended for drinking. Enteric viruses infect the gastrointestinal or respiratory tracts, and are capable of causing a wide range of illness, including diarrhea, fever, hepatitis, paralysis, meningitis and heart disease (American Water Works Association, 1999).
Protozoan parasites are single-celled microorganisms that feed on bacteria found in multicellular organisms, such as animals and humans. Several species of protozoan parasites are transmitted through water in dormant, resistant forms, known as cysts and oocysts. According to the World Health Organization, Cryptosporidium parvum oocysts and Giardia lamblia cysts are introduced to waters all over the world by fecal pollution. The same durable form that permits them to persist in surface waters makes these microorganisms resistant to normal drinking water chlorination (WHO, 2002b). Water systems that filter raw water may successfully remove protozoan parasites.
An emerging pathogen is one that gains attention because it is one of the following:
* a newly recognized disease-causing organism
* a known organism that starts to cause disease
* an organism whose transmission has increased
Source: Guerrant, 1997
Cryptosporidium is an emerging parasitic protozoan pathogen because its transmission has increased dramatically over the past two decades. Evidence suggests it is newly spread in increasingly popular day-care centers and possibly in widely distributed water supplies, public pools and institutions such as hospitals and extended-care facilities for the elderly. Recognized in humans largely since 1982 and the start of the AIDS epidemic, Cryptosporidium is able to cause potentially life-threatening disease in the growing number of immunocompromised patients. Cryptosporidium was the cause of the largest reported drinking water outbreak in U.S. history, affecting over 400,000 people in Milwaukee in April, 1993. More than 100 deaths are attributed to this outbreak. Cryptosporidium remains a major threat to the U.S. water supply (Ibid.).
The EPA is developing new drinking water regulations to reduce Cryptosporidium and other resistant parasitic pathogens. Key provisions of the Long Term 2 Enhanced Surface Water Treatment Rule include source water monitoring for Cryptosporidium; inactivation by all unfiltered systems; and additional treatment for filtered systems based on source water Cryptosporidium concentrations. EPA will provide a range of treatment options to achieve the inactivation requirements. Systems with high concentrations of Cryptosporidium in their source water may adopt alternative disinfection methods (e.g., ozone, UV, or chlorine dioxide). However, most water systems are expected to meet EPA requirements while continuing to use chlorination. Regardless of the primary disinfection method used, water systems must continue to maintain residual levels of chlorine-based disinfectants in their distribution systems.
Giardia lamblia, discovered approximately 20 years ago, is another emerging waterborne pathogen. This parasitic microorganism can be transmitted to humans through drinking water that might otherwise be considered pristine. In the past, remote water sources that were not affected by human activity were thought to be pure, warranting minimal treatment. However, it is known now that all warm-blooded animals may carry Giardia and that beaver are prime vectors for its transmission to water supplies.
There is a distinct pattern to the emergence of new pathogens. First, there is a general recognition of the effects of the pathogen in highly susceptible populations such as children, cancer patients and the immuno-compromised. Next, practitioners begin to recognize the disease and its causative agent in their own patients, with varied accuracy. At this point, some may doubt the proposed agent is the causative agent, or insist that the disease is restricted to certain types of patients. Finally, a single or series of large outbreaks result in improved attention to preventive efforts. From the 1960’s to the 1980’s this sequence of events culminated in the recognition of Giardia lamblia as a cause of gastroenteritis (Lindquist, 1999).
The treatment and distribution of water for safe use is one of the greatest achievements of the twentieth century. Before cities began routinely treating drinking water with chlorine (starting with Chicago and Jersey City in 1908), cholera, typhoid fever, dysentery and hepatitis A killed thousands of U.S. residents annually. Drinking water chlorination and filtration have helped to virtually eliminate these diseases in the U.S. and other developed countries.
Meeting the goal of clean, safe drinking water requires a multi-barrier approach that includes: protecting source water from contamination, appropriately treating raw water, and ensuring safe distribution of treated water to consumers’ taps.
During the treatment process, chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite solution or dry calcium hypochlorite. When applied to water, each of these forms “free chlorine,” which destroys pathogenic (disease-causing) organisms.
Almost all U.S. systems that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. In addition to controlling disease-causing organisms, chlorination offers a number of benefits including:
* Reduces many disagreeable tastes and odors;
* Eliminates slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks;
* Removes chemical compounds that have unpleasant tastes and hinder disinfection; and
* Helps remove iron and manganese from raw water.
As importantly, only chlorine-based chemicals provide “residual disinfectant” levels that prevent microbial re-growth and help protect treated water throughout the distribution system.
The Risks of Waterborne Disease
Where adequate water treatment is not readily available, the impact on public health can be devastating. Worldwide, about 1.2 billion people lack access to safe drinking water, and twice that many lack adequate sanitation. As a result, the World Health Organization estimates that 3.4 million people, mostly children, die every year from water-related diseases.
Even where water treatment is widely practiced, constant vigilance is required to guard against waterborne disease outbreaks. Well-known pathogens such as E. coli are easily controlled with chlorination, but can cause deadly outbreaks given conditions of inadequate or no disinfection. A striking example occurred in May 2000 in the Canadian town of Walkerton, Ontario. Seven people died and more than 2,300 became ill after E. coli and other bacteria infected the town’s water supply. A report published by the Ontario Ministry of the Attorney General concludes that, even after the well was contaminated, the Walkerton disaster could have been prevented if the required chlorine residuals had been maintained.
Some emerging pathogens such as Cryptosporidium are resistant to chlorination and can appear even in high quality water supplies. Cryptosporidium was the cause of the largest reported drinking water outbreak in U.S. history, affecting over 400,000 people in Milwaukee in April 1993. More than 100 deaths are attributed to this outbreak. New regulations from the U.S. Environmental Protection Agency (EPA) will require water systems to monitor Cryptosporidium and adopt a range of treatment options based on source water Cryptosporidium concentrations. Most water systems are expected to meet EPA requirements while continuing to use chlorination.
The Challenge of Disinfection Byproducts
While protecting against microbial contamination is the top priority, water systems must also control disinfection byproducts (DBPs), chemical compounds formed unintentionally when chlorine and other disinfectants react with natural organic matter in water. In the early 1970s, EPA scientists first determined that drinking water chlorination could form a group of byproducts known as trihalomethanes (THMs), including chloroform. EPA set the first regulatory limits for THMs in 1979. While the available evidence does not prove that DBPs in drinking water cause adverse health effects in humans, high levels of these chemicals are certainly undesirable. Cost-effective methods to reduce DBP formation are available and should be adopted where possible. However, a report by the International Programme on Chemical Safety (IPCS 2000) strongly cautions:
The health risks from these byproducts at the levels at which they occur in drinking water are extremely small in comparison with the risks associated with inadequate disinfection. Thus, it is important that disinfection not be compromised in attempting to control such byproducts.
Recent EPA regulations have further limited THMs and other DBPs in drinking water. Most water systems are meeting these new standards by controlling the amount of natural organic material prior to disinfection.
Chlorine and Water System Security
The prospect of a terrorist attack has forced all water systems, large and small, to re-evaluate and upgrade existing security measures. Since September 11th, 2001, water system managers have taken unprecedented steps to protect against possible attacks such as chemical or biological contamination of the water supply, disruption of water treatment or distribution, and intentional release of treatment chemicals.
With passage of the Public Health Security and Bioterrorism Response Act of 2002, Congress required community water systems to assess their vulnerability to a terrorist attack and other intentional acts. As part of these vulnerability assessments, systems assess the transportation, storage and use of treatment chemicals. These chemicals are both critical assets (necessary for delivering safe water) and potential vulnerabilities (may pose significant hazards, if released). Water systems using elemental chlorine, in particular, must determine whether existing protection systems are adequate. If not, they must consider additional measures to reduce the likelihood of an attack or to mitigate the potential consequences.
Disinfection is crucial to water system security, providing the “front line” of defense against biological contamination. However, conventional treatment barriers in no way guarantee safety from biological attacks. Additional research and funding are needed to improve prevention, detection and responses to potential threats.
The Future of Chlorine Disinfection
Despite a range of new challenges, drinking water chlorination will remain a cornerstone of waterborne disease prevention. Chlorine’s wide array of benefits cannot be provided by any other single disinfectant. While alternative disinfectants (including chlorine dioxide, ozone, and ultraviolet radiation) are available, all disinfection methods have unique benefits, limitations, and costs. Water system managers must consider these factors, and design a disinfection approach to match each system’s characteristics and source water quality.
In addition, world leaders increasingly recognize safe drinking water as a critical building block of sustainable development. Chlorination can provide cost-effective disinfection for remote rural villages and large cities alike, helping to bring safe water to those in need.
Chlorination and Public Health
Of all the advancements made possible through science and technology, the treatment and distribution of water for safe use is truly one of the greatest. Abundant, clean water is essential for good public health. Humans cannot survive without water; in fact, our bodies are 67% water! Both the U.S. Centers for Disease Control and Prevention and the National Academy of Engineering cite water treatment as one of the most significant advancements of the last century.
Disinfection, a chemical process whose objective is to control disease-causing microorganisms by killing or inactivating them, is unquestionably the most important step in drinking water treatment. By far, the most common method of disinfection in North America is chlorination.
Prior to 1908, no U.S. municipal water systems chemically disinfected water. Consequently, waterborne diseases exacted a heavy toll in illness and death. Without chlorination or other disinfection processes, consumers are at great risk of contracting waterborne diseases. Figure 1-1 shows the decline in the death rate due to typhoid fever following the introduction of chlorine to U.S. municipal drinking water systems in 1908. As more cities adopted water chlorination, U.S. death rates due to cholera and hepatitis A also declined dramatically. Worldwide, significant strides in public health and the quality of life are directly linked to the adoption of drinking water chlorination. Recognizing this success, Life magazine (1997) declared, “The filtration of drinking water plus the use of chlorine is probably the most significant public health advancement of the millennium.”
The timeline at the bottom of these pages highlights important developments in the history of drinking water chlorination.
Providing Safe Drinking Water: A Multi-Barrier Approach
Meeting the goal of clean, safe drinking water requires a multibarrier approach that includes protecting raw source water from contamination, appropriately treating raw water, and ensuring safe distribution of treated water to consumers’ taps.
Source Water Protection
Source water includes any surface water (rivers and lakes) or groundwater used as a raw water supply. Every drop of rain and melted flake of snow that does not re-enter the atmosphere after falling to the ground wends its way, by the constant pull of gravity, into the vast interconnected system of Earth’s ground- and surface waters. Precipitation ultimately collects into geographic regions known as watersheds or catchment basins, the shapes of which are determined by an area’s topography.
Increasingly, communities are implementing watershed management plans to protect source water from contamination and ecological disruption. For example, stream buffers may be established as natural boundaries between streams and existing areas of development. In addition, land use planning may be employed to minimize the total area of impervious surfaces such as roads and walkways, which prevent water from soaking into the ground. Reservoirs may be protected from contamination by disinfecting wastewater effluents, prohibiting septic system discharges and even controlling beaver activity (Beaver feces are potential sources of the harmful protozoan parasites Giardia lamblia and Cryptosporidium parvum.) Similarly, the Safe Drinking Water Act requires well head protection programs of water systems using groundwater sources. In such programs, the surface region above an aquifer is protected from contaminants that may infiltrate groundwater. Because source water quality affects the kind of treatment needed, watershed management planning is a sustainable, cost-effective step in providing safe drinking water.
Every day, approximately 170,000 (U.S. EPA, 2002) public water systems treat and convey billions of gallons of water through approximately 880,000 miles (Kirmeyer, 1994) of distribution system piping to U.S. homes, farms and businesses. Broadly speaking, water is treated to render it suitable for human use and consumption. While the primary goal is to produce a biologically (disinfected) and chemically safe product, other objectives also must be met, including: no objectionable taste or odor; low levels of color and turbidity (cloudiness); and chemical stability (non-corrosive and non-scaling). Individual facilities customize treatment to address the particular natural and manmade contamination characteristic of their raw water. Surface water usually presents a greater treatment challenge than groundwater, which is naturally filtered as it percolates through sediments. Surface water is laden with organic and mineral particulate matter, and may harbor protozoan parasites such as Cryptosporidium parvum and Giardia lamblia. The graphic on the following page illustrates and describes the four main steps in a water treatment plant employing chlorine disinfection.
In storage and distribution, drinking water must be kept safe from microbial contamination. Frequently, slippery films of bacteria, known as biofilms, develop on the inside walls of pipes and storage containers. Among disinfection techniques, chlorination is unique in that a pre-determined chlorine concentration may be designed to remain in treated water as a measure of protection against harmful microbes encountered after leaving the treatment facility.
In the event of a significant intrusion of pathogens resulting, for example, from a broken water main, the level of the average “chlorine residual” will be insufficient to disinfect contaminated water. In such cases, it is the monitoring of the sudden drop in the chlorine residual that provides the critical indication to water system operators that there is a source of contamination in the system.
Water treatment transforms raw surface and groundwater into safe drinking water. Water treatment involves two types of processes: physical removal of solids (mainly mineral and organic particulate matter) and chemical disinfection (killing/inactivating microorganisms). Treatment practices vary from system to system, but there are four generally accepted basic techniques.
Alum (an aluminum sulfate) or other metal salts are added to raw water to aggregate particles into masses that settle more readily than individual particles.
Coagulated particles fall, by gravity, through water in a settling tank and accumulate at the bottom of the tank, clearing the water of much of the solid debris.
Water from the sedimentation tank is forced through sand, gravel, coal, or activated charcoal to remove solid particles not previously removed by sedimentation.
Chlorine is added to filtered water to destroy harmful microorganisms. An additional amount, known as a “chlorine residual” is applied to protect treated water from re-contamination as it travels throughout the distribution system.
Source: Illustration by Bremmer and Goris Communications.
Chlorine: The Disinfectant of Choice
Chlorine is added to drinking water to destroy pathogenic (disease-causing) organisms. It can be applied in several forms: elemental chlorine (chlorine gas), sodium hypochlorite solution (bleach) and dry calcium hypochlorite.
When applied to water, each of these forms “free chlorine” (see Sidebar: How Chlorine Kills Pathogens). One pound of elemental chlorine provides approximately as much free available chlorine as one gallon of sodium hypochlorite (12.5% solution) or approximately 1.5 pounds of calcium hypochlorite (65% strength). While any of these forms of chlorine can effectively disinfect drinking water, each has distinct advantages and limitations for particular applications.
Almost all water systems that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. Table 2-1 shows the percentage of drinking water systems using each of these methods.
The Benefits of Chlorine
Chlorine disinfectants can reduce the level of many disease-causing microorganisms in drinking water to almost immeasurable levels.
Taste and Odor Control
Chlorine disinfectants reduce many disagreeable tastes and odors. Chlorine oxidizes many naturally occurring substances such as foul-smelling algae secretions, sulfides and odors from decaying vegetation.
Biological Growth Control
Chlorine disinfectants eliminate slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks.
Chlorine disinfectants destroy hydrogen sulfide (which has a rotten egg odor) and remove ammonia and other nitrogenous compounds that have unpleasant tastes and hinder disinfection. They also help to remove iron and manganese from raw water.
How Chlorine Kills Pathogens
How does chlorine carry out its well-known role of making water safe? Upon adding chlorine to water, two chemical species, known together as “free chlorine,” are formed. These species, hypochlorous acid (HOCl, electrically neutral) and hypochlorite ion (OCl-, electrically negative), behave very differently. Hypochlorous acid is not only more reactive than the hypochlorite ion, but is also a stronger disinfectant and oxidant.
The ratio of hypochlorous acid to hypochlorite ion in water is determined by the pH. At low pH (higher acidity), hypochlorous acid dominates while at high pH hypochlorite ion dominates. Thus, the speed and efficacy of chlorine disinfection against pathogens may be affected by the pH of the water being treated. Fortunately, bacteria and viruses are relatively easy targets of chlorination over a wide range of pH. However, treatment operators of surface water systems treating raw water contaminated by the parasitic protozoan Giardia may take advantage of the pH-hypochlorous acid relationship and adjust the pH to be effective against Giardia, which is much more resistant to chlorination than either viruses or bacteria.
Another reason for maintaining a predominance of hypochlorous acid during treatment has to do with the fact that pathogen surfaces carry a natural negative electrical charge. These surfaces are more readily penetrated by the uncharged, electrically neutral hypochlorous acid than the negatively charged hypochlorite ion. Moving through slime coatings, cell walls and resistant shells of waterborne microorganisms, hypochlorous acid effectively destroys these pathogens. Water is made microbiologically safe as pathogens either die or are rendered incapable of reproducing.
Detractors Continue to Challenge Chlorination as a Safe Water Solution for Developing Nations - Chlorine Div
Former PAHO official, Fred Reiff, recounts his experiences battling chlorine misinformation during the Latin American cholera epidemic of the 1990s.
Despite data supporting chlorine's highly beneficial impact on clean water supplies and public health, claims persist that the potential risks of chlorination outweigh the public health value of water disinfection. To me this is comparable to watching the third sequel of a grade Z science fiction movie about a monster that won't die. A case in point is a Greenpeace report currently posted on the organization's website asserting that DBP concerns had no bearing on the spread of disease during the 1991 cholera epidemic that began in Peru and was propagated to almost all countries of Latin America. From personal experience I can confirm that these claims are utter nonsense. I am concerned that such disinformation and half truths might be accepted as fact, resulting in otherwise avoidable disease, suffering, death, and economic impact on the poor people of developing countries.
Why am I qualified to respond? From 1981 through most of 1995, I was an official in the Pan American Health Organization/World Health Organization (PAHO) in a position that offered a very unique vantage point. During this period I was responsible for disseminating the WHO drinking water quality guidelines and fomenting the adoption or updating of national drinking water quality standards. I also was responsible for managing the United Nations Global Environmental Monitoring Programs for Water (for the Americas), the development and promulgation of environmental interventions in disaster preparedness and relief, and the development of appropriate technology for treatment of both potable and waste water. I also served on PAHO's management task force that was formed for the prevention and control of cholera. This level of involvement provided many opportunities for both overall and close-up monitoring of the status of water supply disinfection and its effectiveness as a public health measure in prevention and control of waterborne diseases in all Latin American and the Caribbean countries before, during, and after the introduction of cholera in Peru in 1991.
For many years prior to the cholera outbreak, PAHO had been promoting the disinfection of community water distribution systems and other delivery systems for water for human consumption. Primarily through its Center for Sanitary Engineering and Environmental Science (CEPIS) in Lima, Peru, PAHO collaborated in pilot and demonstration projects for virtually all disinfection methodologies in various countries to ascertain their relative disinfection efficiency, cost effectiveness, and practicality for various cultural and economic situations. Some of them worked well and others were failures. Everything considered, chlorination was almost always found to the most reliable and cost effective.
Until the cholera outbreak erupted in Peru in January-February of 1991, the acute and deadly diarrheal disease had not been prevalent in the Americas since the early 1900's. Immediately upon verification of its presence, PAHO began organizing workshops to inform the appropriate officials of the countries of Latin America (and later Caribbean countries) of the seriousness of this disease and its potential to become an epidemic. We shared the most effective and advanced technologies to detect the pathogen, how to diagnose and treat the disease, the tried and proven methodologies that have been used to prevent cholera, public education strategies, and the epidemiological efforts and methodologies to track and understand the propagation of the disease.
Simultaneously, PAHO headquarters directed each of the PAHO Country Offices to advise health and water agencies to take measures to continuously chlorinate all water distribution and delivery systems. For the population not connected to public water systems, special programs were developed to promote the disinfection of water at the household level. In addition, treatment of the waste products of cholera victims with lime was recommended before its discharge to the sewer systems or the environment, and a list of all preventive measures to be taken by officials and individuals were provided to all appropriate officials. Chlorination was recommended, not only because all of the countries were familiar with this technology, but also because chlorine products were readily available and chlorination was the least costly of the disinfection methodologies. And, most importantly, chlorine is very effective in killing or inactivating Vibrio cholerae, the pathogen of this disease as well as pathogens associated with almost all other waterborne diseases.
Shortly after this directive was issued, I was surprised to learn that some local PAHO officials were encountering pockets of resistance to chlorination from a number of health officials, both in Peru and in other countries. I was specifically told that the reason was their concern for chlorination by-products, especially trihalomethanes. This concern had its origin in press releases and published scientific studies widely disseminated by environmental agencies in the developed countries. I traveled to Peru and other countries and personally met with the health officials and even heads of water agencies who expressed their concern directly to me; some even believed that they might be subjected to a lawsuit if they chlorinated or raised the level of chlorine in their water supplies. I also met other concerned health officials in various cholera workshops and symposiums sponsored by PAHO. Most surprising of all was the discovery that even officials in small towns were aware of disinfection by-products and their alleged negative health effects. It was pointed out to all that when the cholera pathogen is present in a water supply, the risk of contracting the disease is immediate, and that a resulting epidemic could cause thousands of deaths. In contrast, the hypothetical health risk posed by trihalomethanes in levels in excess of those recommended by WHO (and EPA) was one extra death per 100,000 persons exposed for a period of 70 years. Unfortunately, some of these well-meaning, but ill-informed officials had to experience the immense proportional difference in risk before accepting this reality.
Debates over the relative significance of the drinking water pathway for cholera in comparison to other pathways also impeded the rapid implementation of drinking water chlorination. Routes that can be taken by cholera include food, beverage, and ice that have been processed or prepared with contaminated water, unhygienic food handlers, produce that is eaten raw but which has been irrigated with cholera contaminated water, filter feeding shellfish harvested in sewage contaminated water, and casual person-to-person contact. Both practical experience and studies have proven that even if cholera is initially introduced through a pathway other than drinking water, the waterborne pathway will soon be activated unless drinking water is disinfected continuously with an adequate level of disinfectant and measures are taken to prevent recontamination before its consumption. A cholera contaminated distribution system is without doubt the most efficient way to transmit this disease.
It should be noted that throughout the first four years of this epidemic the countries with the highest percentage of continuously and adequately chlorinated water systems had no secondary transmission of cholera, even though the disease was introduced into these countries. Also countries that quickly implemented chlorination were able to bring the epidemic under control. There was also an obvious inverse correlation between the percentage of the population receiving chlorinated water and the incidence of new cases of cholera. In one country with excellent long-term epidemiological surveillance in place, it was found that after implementation of measures to prevent cholera, there was also a significant reduction in typhoid fever and infectious hepatitis.
Conversely, those countries that were not able (for whatever reason) to implement chlorination of water supplies on a timely basis, suffered recurring annual epidemics until a sufficient percentage of the population had developed immunity, preventing further epidemic propagation of the disease. Typically there were a number of reasons for delay in implementing widespread chlorination of drinking water supplies. However, no obstacle was harder to overcome than the incorrect perception of risks posed by disinfection by-products relative to the very real and deadly threat of cholera.
To reduce the spread of cholera in areas of abject poverty where household were not connected to water distribution systems PAHO worked in concert with the U.S. Centers for Disease Control and Prevention (CDC) and the University of North Carolina to develop, test, and microbiologically and epidemiologically monitor the results of a methodology to purify the available water at the household level. The end result was chlorination of the household water in containers that were specifically designed to preclude subsequent contamination during storage and use. The annual cost of this intervention was found to be less than $2.00 per family, the major cost being the container. The annual cost of the calcium hypochlorite was less than fifty cents per family. Not only did this prove effective for Latin America but it also led to global health organizations adopting this or similar programs as a viable interim health measure for developing countries in Africa and Asia.
Since the cholera outbreak of 1991, many nations have embraced what is known as the "Precautionary Principle", a protocol acknowledging that uncertainty is inherent in managing emerging risks. The thrust of public health management in the principle is to take steps to reduce potential harm, even when uncertainties remain. Yet a true precautionary approach also means that you do not do away with a proven health intervention. This concept was clearly stated by Dr. Carlyle Macedo, Director of PAHO in his address to the 1992 International Conference on the Safety of Water Disinfection, Balancing the Chemical & Microbiological Risks sponsored by the International Life Sciences Institute.
"In developing countries, the primary public health concern for water supplies should remain preventing them from becoming an efficient vehicle for the widespread transmission of enteric diseases. This concern should not be overshadowed in any way in our efforts to also address the tertiary concern of minimizing the relatively small risk stemming from disinfection by-products…
The high incidence of diseases that are related to water supply and sanitation are primarily a reflection of the social and economic inequities and marginalization that unfortunately still exist in our hemisphere. Basically the people that suffer the most from these diseases have so few economic resources that all but the simplest and least expensive of interventions to reduce their risk of exposure to the many waterborne pathogens are beyond their means. Under such circumstances the disinfection of drinking water with chlorine at the household level, is usually the most viable and cost-effective public health intervention available. To cause these people to abandon chlorination is not only unwise, but cruel, if the alternative is beyond their economic and technical means. Unless there is a simple alternative at an affordable cost, these people should not be frightened away from chlorinating their water. This will only increase their suffering and decrease their life expectancy."
To protect public health, particularly in developing regions, applying the precautionary principle requires use of practical, affordable technologies and a realistic balancing of known and uncertain risks.
Fred M. Reiff, an engineer, is a former official of the Pan American Health Organization/World Health Organization. He retired from that organization in 1995 but continues to serve as an independent international consultant.
Balancing the risks of waterborne pathogens and disinfection byproducts (DBPs) is an evolving challenge for the modern water treatment professional. Widespread disinfection of drinking water, approximately a century old, is regarded as a major public health victory over typhoid fever, cholera and other waterborne diseases. Only in the past 30 years has science demonstrated a potential "downside" to mass water treatment: the formation of DBPs, families of unwanted compounds resulting from the chemical reaction of disinfectants with the organic matter in natural waters. Increasingly, scientists and regulators are addressing the complex presence of DBPs in treated water. Some of these compounds have been regulated. Now, new research demonstrates that with only an incomplete knowledge of the universe of DBPs and their potential hazards, current regulations may have unintended consequences.
The U.S. Environmental Protection Agency (EPA), through its 1998 Stage 1 Disinfectants and Disinfection Byproducts Rule, attempts to manage DBP risk from chlorinated drinking water by regulating two families of DBPs-trihalomethanes (THMs) and haloacetic acids (HAAs). To reduce the presence of these compounds substantially, many water treatment facilities have begun to substitute chloramines for chlorine as a secondary disinfectant. Some systems are also adopting alternatives such as ozone and chlorine dioxide for primary disinfection, although chlorine remains the most popular choice by far. Employing a different tactic, other systems choose to reduce DBP formation by more effectively removing organic matter in source water prior to disinfection. Unfortunately, there is no "one size fits all" solution to managing DBP levels. Facilities must consider the natural chemistry and quality of their source water and their available resources, and plan accordingly.
But there is complicating news: A 2002 nationwide EPA study demonstrates that certain unregulated DBPs are present in drinking water in concentrations on par with those that are regulated. And while alternative disinfectants reduce the presence of THMs and HAAs relative to chlorination, alternate disinfectants can produce higher levels of unregulated DBPs. For example, chloramination of natural waters containing high levels of bromine results in iodinated (iodine-containing) DBPs, one of which is more toxic to cells of mammals than any DBP ever identified.
Disinfection Byproducts: Many and Varied
Hundreds of DBPs have been reported in the scientific literature since EPA scientists first found low levels of chloroform in chlorinated drinking water in 1974. Thirty years later, EPA estimates that less than half of all chlorinated DBPs have been identified. Most of the successfully characterized DBPs are easily extracted from water using analytical techniques; those more difficult to extract remain a challenge to identify. Although substantial progress has been made in investigating chlorinated HAAs and THMs, the body of knowledge on the large number of DBPs resulting from alternative disinfectants is meager. EPA is attempting to characterize all chemicals formed during water treatment so that it can minimize public exposure to the most potentially hazardous DBPs while still maintaining microbiologically safe, healthful drinking water.
Gathering Data Through the Nationwide Disinfection By-product (DBP) Occurrence Study
The Nationwide Disinfection By-product Occurrence Study was undertaken by EPA to characterize and quantify DBPs formed throughout the United States. Drinking water across the country was sampled. To limit the number of compounds analyzed to a manageable quantity, EPA experts were asked to prioritize, by potential toxicity, over 500 DBPs reported in the literature. The result is a list of approximately 50 priority compounds. EPA's goal is to conduct a complete assessment of DBPs formed by different treatments in various regions of the nation.
An important result of the EPA study is the development of information about DBPs from increasingly popular alternative disinfectants. The table below outlines the significant prioritized DBPs associated with each alternative disinfection technique:
Levels of many of the prioritized DBPs resulting from the treatments listed above are higher than levels of THMs and HAAs resulting from chlorination. These study results have implications for utilities considering replacing chlorination with alternative disinfection methods to meet EPA's DBP regulations. A facility treating source water containing naturally elevated bromine levels, for example, might consider avoiding chloramine treatment.
Understanding the Big Picture
Widespread drinking water treatment remains today no less a public health triumph than it was a century ago. A safe, abundant water supply that virtually eliminates waterborne disease frees a society to pursue greater goals. The immeasurable value of safe water to human life is reflected in the United Nations Millennium Goal to "halve, by 2015, the proportion of people without sustainable access to safe drinking water and basic sanitation."
Today's water treatment professionals are faced with a growing database of complex information on DBPs. Their challenge will be to map out the optimum course for managing these compounds, taking into consideration the unique characteristics of their source water and keeping in mind the first priority--eliminating waterborne pathogens.
In a campaign timed to coincide with October 2007, Breast Cancer Awareness Month, a web-based company claims that its PINK water filter products reduce women’s breast cancer risk by removing chlorine from water. The company’s claims are not supported by facts. The U.S. Environmental Protection Agency (EPA) has determined that chlorine levels meeting current drinking water regulations do not pose any known or expected health risks. No U.S. government health agency considers chlorine to be a potential carcinogen.
The company supports its claim by citing a small 1992 study that examined breast cancer and women’s exposures to the banned substances — DDT/DDE and PCBs. These compounds are not related to water chlorination. Additionally, since the 1970s, their production has been prohibited. This 1992 study cited by the water filter company was followed by several larger studies probing a potential link between breast cancer and these substances. After four years reviewing all the relevant studies, the National Academy of Sciences, one of the premier scientific organizations in the U.S., concluded in 1999 that research does not support an association between DDT/DDE and PCBs and breast cancer.
But back to chlorinated water…Chlorine is added to drinking water to help protect public health by destroying disease-causing bacteria, viruses and parasites. Before cities began treating drinking water with chlorine — starting with Chicago and Jersey City almost a century ago — cholera, typhoid fever, hepatitis A and dysentery killed thousands of U.S. residents annually. Today, the vast majority of U.S. water systems that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. Only chlorine-based disinfectants provide “residual disinfectant” levels that help protect treated water as it journeys from the treatment plant to the tap.
EPA regulates chlorine levels in drinking water to pose no risk of adverse health effects. Not to the breast or to any other organ of the human body.
The Water Quality Association, which represents manufacturers of home water treatment products, states in its Code of Ethics that statements “which deceptively disparage publicly or privately supplied water…. shall not be used.”
Breast cancer is an emotional, devastating and potentially life-threatening illness. Baseless claims as to its causes can only serve to confuse and frustrate the public.