Ph DEn M Seminar in Environmental Science - DE LARA

Nueva Ecija University of Science and Technology Cabanatuan City Graduate School In Partial Fulfillment of the Requirements In DEnM 315 – Seminar in Environmental Science Report on: E Wastes & Radiation Presented by: ENGR. RYAN JOHN L. DE LARA PhDEnM Student Submitted to: DR. MIGUEL SANTOS Professor January 2014 E-Waste Introduction Electronic waste, e-waste, e-scrap, or Electronic-disposal, waste electrical and electronic equipment (WEEE) describes discarded electrical or electronic devices. There is a lack of consensus as to whether the term should apply to resale, reuse, and refurbishing industries, or only to a product that cannot be used for its intended purpose. Informal processing of electronic waste in developing countries may cause serious health and pollution problems, though these countries are also most likely to reuse and repair electronics. All electronic scrap components, such as CRTs, may contain contaminants such as lead, cadmium, beryllium, or brominated flame retardants. Even in developed countries recycling and disposal of e-waste may involve significant risk to workers and communities and great care must be taken to avoid unsafe exposure in recycling operations and leaking of materials such as heavy metals from landfills and incinerator ashes. Scrap industry and USA EPA officials agree that materials should be managed with caution. Definition "Electronic waste" may be defined as discarded computers, office electronic equipment, entertainment device electronics, mobile phones, television sets and refrigerators. This definition includes used electronics which are destined for reuse, resale, salvage, recycling, or disposal. Others define the re-usables (working and repairable electronics) and secondary scrap (copper, steel, plastic, etc.) to be "commodities", and reserve the term "waste" for residue or material which is dumped by the buyer rather than recycled, including residue from reuse and recycling operations. Because loads of surplus electronics are frequently commingled (good, recyclable, and non-recyclable), several public policy advocates apply the term "e-waste" broadly to all surplus electronics. Cathode ray tubes (CRTs) are considered one of the hardest types to recycle. CRTs have relatively high concentration of lead and phosphors (not to be confused with phosphorus), both of which are necessary for the display. The United States Environmental Protection Agency (EPA) includes discarded CRT monitors in its category of "hazardous household waste" but considers CRTs that have been set aside for testing to be commodities if they are not discarded, speculatively accumulated, or left unprotected from weather and other damage. The EU and its member states operate a system via the European Waste Catalogue (EWC) - a European Council Directive, which is interpreted into "Member state law". In the UK (EU member state), this is in the form of the List of Wastes Directive. However, the list (and EWC) gives broad definition (EWC Code 16 02 13*) of Hazardous Electronic wastes, requiring "waste operators" to employ the Hazardous Waste Regulations (Annex 1A, Annex 1B) for refined definition. Constituent materials in the waste also require assessment via the combination of Annex II and Annex III, again allowing operators to further determine whether a waste is hazardous. Debate continues over the distinction between "commodity" and "waste" electronics definitions. Some exporters are accused of deliberately leaving difficult-to-recycle, obsolete, or non-repairable equipment mixed in loads of working equipment (though this may also come through ignorance, or to avoid more costly treatment processes). Protectionists may broaden the definition of "waste" electronics in order to protect domestic markets from working secondary equipment. The high value of the computer recycling subset of electronic waste (working and reusable laptops, desktops, and components like RAM) can help pay the cost of transportation for a larger number of worthless pieces than can be achieved with display devices, which have less (or negative) scrap value. In A 2011 report, "Ghana E-Waste Country Assessment", found that of 215,000 tons of electronics imported to Ghana, 30% were brand new and 70% were used. Of the used product, the study concluded that 15% was not reused and was scrapped or discarded. This contrasts with published but uncredited claims that 80% of the imports into Ghana were being burned in primitive conditions. How Much E-waste Do We Generate? Whether trashed or recycled, what are we getting rid of each year in the U.S.? The EPA’s most recent e-waste report (summarized in the table on the previous page) shows that we got rid of (we trashed or recycled) 142,000 computers and over 416,000 mobile devices EVERY DAY!! In 2011, we generated 3.41 million tons of e-waste in the U.S. Of this amount, only 850,000 tons or 24.9 % was recycled, according to the EPA (up from 19.6 in 2010). The rest was trashed – in landfills or incinerators. These EPA numbers are for “selected consumer electronics” which include products such as TVs, VCRs, DVD players, video cameras, stereo systems, telephones, and computer equipment.“2 Also see Figure 1, below. “Some 20 to 50 million metric tons of e-waste are generated worldwide every year, comprising more than 5% of all municipal solid waste. When the millions of computers purchased around the world every year (183 million in 2004) become obsolete they leave behind lead, cadmium, mercury and other hazardous wastes.” Release of iPad 5 greated surge of tablet trade-ins “Consumers are trading in their iPads and other tablets at an "unprecedented rate" to buy the newest offerings from Apple, Google and Microsoft, according to SellCell, an electronics trade-in website.” Sales in Electronics - How Much Electronics Are We Buying? Note: Statistics on sales are expressed in terms of “units shipped” from the manufacturers into their various sales channels, unless otherwise noted. In 2012, the average U.S. household spent $1,312 on consumer electronics (CE) products a year, according to a study, by the Consumer Electronics Association (CEA). The average household reports owning 24 discrete CE products. Globally, we will buy 1.6 billion consumer electronics in 2011, up from 1.56 billion in 2010, according to market research firm iSupply. According to the Consumer Electronics Association (CEA) sales of smart phones and tablet computers are expected to drive annual consumer electronics sales to over $206 billion in 2012 — the first time above the $200 billion mark.” If you stacked these iDevices into one column, it would reach over 4200 MILES high, well into outer space. If you then laid that iDevice snake on its side, it would reach from Vancouver to Bogota, Colombia, or Oslo to Mumbai. A survey by the National Retail Federation says we will buy over 7.5 million new TVs for the 2013 Super bowl. This is up from 5.1 million new TVs to watch the 2012 Super bowl, 4.6 million in 2011, 3.6 million in 2010 and 2.6 million in 2009. According to a 2013 study by CEA, 98% of US households have at least one TV. Effects of E Waste Content to the Human Body E-waste contains a number of toxic substances which are not only dangerous for the environment but also for the people living in the immediate area of e-waste recycling and disposal sites. The cathode ray tubes (CRTs) in computer and television monitors contain lead - which is poisonous to the nervous system - as do circuit boards. Mercury - like lead - a neurotoxin, is used in flat-panel display screens. Some batteries and circuit boards contain cadmium, known to be a carcinogen. Lead is found in a wide variety of cell phone components including the circuit boards, batteries and as a stabilizer in PVC products. Lead exposure can cause damage to the reproductive, blood and nervous systems. Mercury is used in the cell phone’s battery, crystal displays and circuit boards. A single cell phone contains up to 2 grams of mercury. Mercury exposure contributes to brain and kidney damage. Arsenic is found in the microchips of many electronic devices including mobile phones. In high doses, arsenic poisoning is lethal. Low levels of exposure cause negative impacts on skin, liver, nervous and respiratory systems. Cadmium is used in the battery of a cell phone. It is associated with deficits in cognition, learning, behavior and neuromotor skills in children. It has also been linked to kidney damage. Chlorine is a component of plastics used in cell phones, specifically polyvinyl chloride (PVC). PVC makes up about 30% of the cell phone. Exposure to improperly disposed ­­­­chlorine causes tissue damage and the destruction of cell structure. Bromine is a component in a group of fire retardant chemicals known as brominated flame retardants. It is associated with cognitive and developmental deficits. Studies have shown that bromine contributes to the disruption in the thyroid hormone balance, brain damage and cancer. To Make Everything Clear The rapid pace of technological change in the field of electronics has made appliances for homes and office equipment both affordable and widely used. The extreme growth rates but also ever increasing obsolescence rates result in large quantities of electrical and electronic equipment being added to the waste stream. Electronics are quickly becoming a significant portion of the materials sent to local landfills. Computers, radios, fax machines, cellular telephones and personal digital assistants are becoming items of concern in the waste stream. Advances in technology, as well as the decreasing price of most electronics, has led to an increase in the volume of outdated items that require proper disposal, typically called electronic waste. Electronic waste, popularly known as ‘e-waste’ (E. Pehlivan12 et al.,2009) can be defined as electronic equipments / products connects with power plug, batteries which have become obsolete due to: Advancement in technology Changes in fashion, style and status Nearing the end of their useful life. The processing of electronic waste in developing countries causes serious health and pollution problems due to lack of containment, as do unprotected land filling (due to leaching) and incineration. Classification of E-WASTE: E-waste encompasses ever growing range of obsolete electronic devices such as computers, servers, main frames, monitors, TVs & display devices, telecommunication devices such as cellular phones & pagers, calculators, audio and video devices, printers, scanners, copiers and fax machines besides refrigerators, air conditioners, washing machines, and microwave ovens, e-waste also covers recording devices such as DVDs, CDs, floppies, tapes, printing cartridges, military electronic waste, automobile catalytic converters, electronic components such as chips, processors, mother boards, printed circuit boards, industrial electronics such as sensors, alarms, sirens, security devices, automobile electronic devices. The classification of e-waste is shown in the form of a flowchart in Fig 2.1. E-WASTE HAZARDS: Electronic waste accounts for 70 percent of the overall toxic waste currently found in landfills. In addition to valuable metals like aluminum, electronics often contain hazardous materials like mercury. When placed in a landfill, these materials (even in small doses) can contaminate soil as well as drinking water. E-waste contains different hazardous materials which are harmful to human health and the environment if not disposed of carefully. While some naturally occurring substances are harmless in nature, their use in the manufacture of electronic equipment often results in compounds which are hazardous (e.g. chromium becomes chromium VI). The following table gives a selection of the mostly found toxic substances in e-waste and the various health hazards caused. Table 3.1 E Waste Hazards Substance: Halogenated compounds: Occurrence in e- waste: Health relevance: PCB (polychlorinated biphenyls) condensers, transformers Cause cancer, effects on the immune system, reproductive system, nervous system, endocrine system and other health effects. Persistent and bio accumulatable. • TBBA (tetrabromobisphenol-A) • PBB (polybrominated biphenyls) • PBDE (polybrominated diphenyl ethers) Fire retardants for plastics (thermoplastic components, cable insulation) TBBA is presently the most widely used flame retardant in printed wiring boards and covers for components can cause long-term period injuries to health acutely poisonous when burned Chlorofluorocarbon (CFC) cooling unit, insulation foam Combustion of halogenated substances may cause toxic emissions. PVC (polyvinyl chloride High) cable insulation Temperature processing of cables may release chlorine, which is converted to dioxins and furans. Heavy metals and other metals: Arsenic small quantities in the form of gallium arsenide within light emitting diodes acutely poisonous and on a long-term perspective injurious to health Barium Getters in CRT may develop explosive gases (hydrogen) if wetted Beryllium power supply boxes which contain silicon controlled rectifiers, beam line components Harmful if inhaled Cadmium rechargeable NiCd-batteries, fluorescent layer (CRT screens), printer inks and toners, photocopying -machines (photodrums) acutely poisonous and injurious to health on a long-term perspective Chromium VI Data tapes, floppy-disks acutely poisonous and injurious to health on a long-term perspective causes allergic reactions Gallium arsenide Light-emitting diode (LED) injurious to health Lead CRT screens, batteries, printed wiring boards causes damage to the nervous system, circulatory system, kidneys causes learning disabilities in children Lithium Li-batteries may develop explosive gases (hydrogen) if wetted Mercury Is found in the fluorescent lamps that provide backlighting in LCDs, in some alkaline batteries and mercury wetted switches acutely poisonous and injurious to health on a long-term perspective Nickel rechargeable NiCd-batteries or NiMH batteries, electron gun in CRT may cause allergic reactions Rare earth elements (Yttrium, Europium) fluorescent layer (CRT-screen) irritates skin and eyes Selenium toxic when inhaled older photocopying-machines (photo drums) exposure to high levels may cause adverse health effects Zinc sulphide Is used on the interior of a CRT screen, mixed with rare metals Toxic when inhaled Others: Toxic organic substances condensers, liquid crystal display Toner Dust Toner cartridges for laser printers / copiers Health risk when dust is inhaled risk of explosion Radioactive substances Americium Medical equipment, fire detectors May cause cancer when inhaled Electronics and electrical equipment seem efficient and environmentally-friendly, but there are hidden dangers associated with them once these become e-waste. The harmful materials contained in electronics products (Cynthia A. Bilyet al., 2008); coupled with the fast rate at which we’re replacing outdated units, pose a real danger to human health if electronics products are not properly processed prior to disposal (Jae-Min Yoo19et al.,2009). Electronic products like computers and cell phones contain a lot of different toxins (Daniel A. Vallero et al., 2002). For example, cathode ray tubes (CRT) of computer monitors contain heavy metals such as lead, barium and cadmium, which can be very harmful to health if they enter the water system. These materials can cause damage to the human nervous system and respiratory systems. Flame- retardant plastics used in electronics casings, release particles that can damage human endocrine functions. These are the types of things that can happen when unprocessed e-waste is put directly in landfill. E-WASTE SCENARIO: E-Waste is a global concern today. It can have far-reaching adverse effects on the environment if not dealt with immediately. Awareness of e-waste management is the key to getting more customers to come forward and dispose of their e-waste in a safe manner. E-Waste in the global context: The use of electronic devices has proliferated in recent decades, and proportionately the quantity of electronic devices that are disposed of, is growing rapidly throughout the world. A study found that every year, 20 to 50 million tons of e-waste are generated worldwide. In 1994, it was estimated that approximately 20 million Personal Computers (PC) became obsolete. By 2004, this figure was to increase to over 100 million PC. This fast growing waste stream is accelerating because the global market for PC is far from saturation and the average lifespan of a Personal Computer (PC) is decreasing rapidly. E-waste is a global issue for two main reasons: 1. Developing countries own a substantial share of e-waste. For example, of the estimated 20-50 million tons of e-waste discarded annually worldwide, Asian countries discard an estimated 12 million tons. This share will likely only increase with the rapidly developing economies of China and India, who will have 178 million and 80 million new computers, respectively, out of the global total of an estimated 716 million new computer users by 2010. 2. E-waste is often sent for recycling and refurbishing in developing countries (David Naquib Pellow, 2007) where labor is relatively cheap, and, once there, can simply be land filled, for example, 50-80 percent of the e-waste collected for recycling in the US is exported. In USA, it accounts 1% to 3% of the total municipal waste generation. In European Union (EU), e-waste is growing three times faster than average annual municipal solid waste generation. A recent source estimates that total amount of e-waste generation in EU ranges from 5 to 7 million tons per annum or about 14 to 15 kg per capita and is expected to grow at a rate of 3% to 5% per year. In developed countries, currently it equals 1% of total solid waste generation and is expected to grow to 2% by 2010. FRIENDLY WAY TO HANDLE E-WASTE: There are many ways to deal with e-waste. As the adage goes “prevention is better than cure” it is wise to prevent or minimize the production of e-waste. Reusing the parts and various components of e-waste is another option which reduces the total volume of e-waste to be treated or disposed off. (Anne E. Maczulak et al.,2009) Recycling is changing the original product and using it to produce something new. Recycling also reduces the content of e-waste to be disposed. When methods like open burning or incineration are used for disposing e-waste, the energy so produced can be recovered and put to use for lighting or other purposes. The least favored method of handling e-waste is to dispose it off. Disposal methods not only cause pollution but also lead to generation of by- products which have to be dealt with separately. Figure 3.1 Pyramid showing friendly way to handle e-waste Source: MPCB VARIOUS METHODS OF E-WASTE DISPOSAL: E-waste management practices comprise of various means of final disposal of end-of-life equipment. In the hierarchy of end-of-life disposal methods, landfilling is considered the most harmful, and recycling the most environmentally tolerable Various methods of e-waste disposal are: Incineration Open burning Landfilling Incineration: Incineration is the process of destroying waste through burning. Because of the variety of substances found in e-waste, incineration is associated with a major risk of generating and dispersing contaminants and toxic substances. The gases released during the burning and the residue ash is often toxic (R. E. Hester et al.,2004). This is especially true for incineration or co-incineration of e-waste with neither prior treatment nor sophisticated flue gas purification. Studies of municipal solid waste incineration plants have shown that copper, which is present in printed circuit boards and cables, acts a catalyst for dioxin formation when flame-retardants are incinerated. These brominated flame retardants when exposed to low temperature (600-800°C) can lead to the generation of extremely toxic polybrominated dioxins (PBD) and furans. PVC, which can be found in e-waste in significant amounts, is highly corrosive when burnt and also induces the formation of dioxins. Advantages of incineration: Advantage of incineration of e-waste is the reduction of waste volume and the utilization of the energy content of combustible materials. Some plants remove iron from the slag for recycling. By incineration some environmentally hazardous organic substances are converted into less hazardous compounds. Disadvantages of incineration: Disadvantage of incineration are the emission to air of substances escaping flue gas cleaning and the large amount of residues from gas cleaning and combustion. Incineration also leads to the loss valuable of trace elements which could have been recovered had they been sorted and processed separately. Open-burning: Open burning is the process of destroying the waste by burning it under uncontrolled conditions. Disadvantages of open burning: Since open fires burn at relatively low temperatures, they release many more pollutants than in a controlled incineration process at an MSWI-plant. Inhalation of open fire emissions can trigger asthma attacks, respiratory infections, and cause other problems such as coughing, wheezing chest pain, and eye irritation (Mackenzie, et al., 2005). Chronic exposure to open fire emissions may lead to diseases such as emphysema and cancer. For example, burning PVC releases hydrogen chloride, which on inhalation mixes with water in the lungs to form hydrochloric acid. This can lead to corrosion of the lung tissues, and several respiratory complications. Often fires burn with a lack of oxygen, forming carbon monoxide, which poisons the blood when inhaled. The residual particulate matter in the form of ash is prone to fly around in the vicinity and can also be dangerous when inhaled. Soil and sediment collected in the vicinity of an open electronic waste disposal and recycling facility. The PBD were detected in the soil and sediment samples at levels of 0.26–824 Ng/g (dry weight). Many of the chemicals released are highly toxic, some may affect children’s developing reproductive systems, while other can affect brain development and the nervous system. The samples of soil/ash from open burning sites generally contained high levels of many metals that are known to be present in electronic devices, some of which have toxic properties (Paul T William, et al., 2005). Numerous organic chemical pollutants were also identified. Similarities were found between the samples from the different open burning sites, with regard to those metals present at high levels and the range of organic chemicals present. Landfilling: The most common method of managing E-waste has been landfilling (Amalendu Baqchi et al., 2004) While the weight represented by used electronics is not dramatic, the volume that these items represent in landfills is proportionally more significant because of the bulk and rigidity of these materials. Furthermore, as some electronic items contain hazardous material, the proper management of those items is important. In addition, electronic items are made with valuable materials that are a great source of recoverable commodities including steel, glass, plastic, and precious metals. Discarded electronics often end up in landfills. It has become common knowledge that all landfills leak. Even the best "state of the art" landfills are not completely tight throughout their lifetimes and a certain amount of chemical and metal leaching will occur (Paul T William et al., 2005). The situation is far worse for older or less stringent dump sites. LEACHING OF E-WASTE: Leachate is the liquid that drains or 'leaches' from a landfill; it varies widely in composition regarding the age of the landfill and the type of waste it contains (David Hollansky et al.,2004). It can usually contain both dissolved and suspended materials. Disposal of e-wastes is one of the main reasons for leaching. Computer wastes that are land filled produces contaminated leachates which eventually pollute the groundwater. Acids and sludge obtained from melting computer chips, if disposed on the ground causes acidification of soil. Incineration of e-wastes can emit toxic fumes and gases, thereby polluting the surrounding air. Improperly monitored landfills can cause environmental hazards. Mercury will leach when certain electronic devices, such as circuit breakers are destroyed. The same is true for polychlorinated biphenyls (PCB) from condensers. When brominated flame retardant plastic or cadmium containing plastics are landfilled, both polybrominated diphenyl ethers (PBDE) and cadmium may leach into the soil and groundwater. It has been found that significant amounts of lead ion are dissolved from broken lead containing glass, such as the cone glass of cathode ray tubes, gets mixed with acid waters and are a common occurrence in landfills. Dynamic Leaching Test Dynamic leaching test (DLT) is employed to study the leaching mechanism and to evaluate the potential leaching hazards of various E-waste components under landfill conditions. The samples include the PC motherboards, hard disk drives, floppy disk drives, CD/DVD drives, power supply units, and cell phones. In the test, a specimen- for instance a whole piece of motherboard - is cleaned of dirt and rinsed by deionizer water, then placed in a test container on top of the supports built inside the container. The containers are filled with two types of leaching fluids. The liquid-to-solid ratio of 10:1 on weight basis is used (James E. Kilduff, 2000). Leaching cycles of 3 to 10 days were used. After each leaching cycle, the leaching fluid is renewed by the fresh one and analyzed for different toxic constituents. RECYCLING: Nowadays computer has been as important as oxygen. Without computer no one can live. All are looking at the advantages it has been producing but there are disadvantages equal to advantages. One of them is the electronic wastes produced by the computer. These electronic wastes contain toxic substances like mercury, lead, cadmium etc. These substances cause harm to the Environment. Recycling (Carl A. Zimring et al.,2005) is one of those concepts everyone embraces. Yet, when it comes to electronics—TVs, monitors, computers, and peripherals—why do so few of us actually do it? According to figures from the EPA (Environmental Protection Agency), only about 13.6% of so-called e-waste was recycled in 2007, the rest being diverted to municipal landfills or storage. The rate is a significant improvement from the 10% recycled in 2000; however, it’s a far cry from the two-thirds of major appliances—things such as refrigerators and washing machines—that are diverted from the dump. Recycling of e-waste is not required merely because it is mandatory or environmental requirement, but is also essential to avoid bad publicity when computers and other office automation systems are found in landfill or third world countries, consequently, the industry is on the brink of a paradigm shift with respect to cost avoidance v/s risk avoidance. Purpose of recycling e-waste: Most electronic devices contain a variety of materials, including metals, which can be recovered for recycling. Recycling waste electronics saves resources and protects the Earth because new metals don't have to be mined (Denise Di Ramio et al., 2008). In addition, some electronic products contain high enough levels of certain materials, such as lead, that render them hazardous waste when disposed. Hazardous wastes cannot be disposed with municipal trash. Apart from this other few reasons for recycling are as follows: Good For Our Economy -companies rely on recycling programs to provide the raw materials they need to make new products. Creates Jobs Reduces Waste (Frank Ackerman et al.,2007) Good For The Environment -Recycling requires far less energy, uses fewer natural resources, and keeps waste from piling up in landfills. Saves Energy -Recycling offers significant energy savings over manufacturing with virgin materials. Preserves Landfill Space -No one wants to live next door to a landfill. Recycling preserves existing landfill space. Prevents Global Warming Reduces Water Pollution -Making goods from recycled materials generates far less water pollution than manufacturing from virgin materials. Creates New Demand -Recycling and buying recycled products creates demand for more recycled products, decreasing waste and helping our economy Process of Recycling: The process followed is as under: Manual separation of glass & large ferrous Shredding of the remaining items Magnetic separation for iron/steel Eddy current separation for aluminum Manual separation of copper and other mix Re-shredding of mix particles Segregation of Printed Circuit Boards, CRT separation Disposal of heavy hazardous substances Recovery of precious metals by the renowned refinery Sale of recovered commodities to respective smelting companies Figure 4.1 Recycling Process SOME INTERNATIONAL RESPONSES TO E-WASTE: United States: In September 2003, California passed the “Electronic Waste Recycling Act of 2003” (SB20), USA’s first comprehensive electronics recycling law, establishing a funding system for the collection and recycling of certain electronic wastes. European Union: On January 27, 2003, the EU parliament passed a directive that requires producers of electronics to take responsibility, financial and otherwise, for recovery and recycling of E-Waste. Japan: Since April 2001, manufacturers have had to recycle appliances, televisions, refrigerators, and air conditioners. Under a new law, manufacturers would charge a recycling fee to consumers. OECD: The OECD has developed international guidelines on the “environmentally sound management” (ESM) of used and scrap personal computers. China: The Standing Committee of the 9th NPC promulgated a law in 2002, requiring compulsory retrieval of used industrial products. Netherlands: In 1998, passed, “The Disposal of White and Brown Goods Decree”. It requires manufacturers and importers of electrical and electronic equipment sold in the country to take back their end-of-life products. RADIATION Overview Radiation is energy in the form of waves or streams of particles. There are many kinds of radiation all around us. When people hear the word radiation, they often think of atomic energy, nuclear power and radioactivity, but radiation has many other forms. Sound and visible light are familiar forms of radiation; other types include ultraviolet radiation (that produces a suntan), infrared radiation (a form of heat energy), and radio and television signals. Figure 1 presents an overview of the electromagnetic spectrum; section 3 will go into greater detail on the different types of radiation. Figure 1 – The Electromagnetic Spectrum Uncontrolled use of man-made radiation carries a potential risk to the health and safety of workers and the public. Introduction to Radiation All life has evolved in an environment filled with radiation. The forces at work in radiation are revealed upon examining the structure of atoms. Atoms are a million times thinner than a single strand of human hair, and are composed of even smaller particles – some of which are electrically charged. Atoms: Where all matter begins Atoms form the basic building blocks of all matter. In other words, all matter in the world begins with atoms – they are elements like oxygen, hydrogen, and carbon. An atom consists of a nucleus – made up of protons and neutrons that are kept together by nuclear forces – and electrons that are in orbit around the nucleus (see Figure 2). The nucleus carries a positive charge; protons are positively charged, and neutrons do not carry a charge. The electrons, which carry a negative charge, move around the nucleus in clouds (or shells). The negative electrons are attracted to the positive nucleus because of the electrical force. This is how the atom stays together. Each element is distinguished by the number of protons in its nucleus. This number, which is unique to each element, is called the “atomic number”. For example, carbon has six protons; therefore, its atomic number is 6 on the periodic table (see Figure 3). In an atom of neutral charge, the atomic number is also equal to the number of electrons. An atom’s chemical properties are determined by the number of electrons, which is normally equal to the atomic number. Each element is distinguished by the number of protons in its nucleus. This number, which is unique to each element, is called the “atomic number”. For example, carbon has six protons; therefore, its atomic number is 6 on the periodic table (see Figure 3). In an atom of neutral charge, the atomic number is also equal to the number of electrons. An atom’s chemical properties are determined by the number of electrons, which is normally equal to the atomic number. Figure 3 – Periodic Table of Elements Atoms from one or more elements combine to form molecules. A molecule of water, for example, is formed of two atoms of hydrogen bound to one atom of oxygen (H2O). A nuclide is a specific type of atom characterized by the number of protons and neutrons in its nucleus, which approximates the mass of the nuclide. The number that is sometimes given with the name of the nuclide is called its mass number (the total number of protons and neutrons in the nucleus). For example, a nuclide of carbon with 6 protons and 6 neutrons is called carbon-12. Isotopes An isotope is a variant of a particular chemical element. While all isotopes of a given element have the same number of protons, each isotope has a different number of neutrons. For example, hydrogen has three isotopes (or variants): hydrogen-1 (contains one proton and no neutrons) hydrogen-2, which is called deuterium (contains one proton and one neutron) hydrogen-3, which is called tritium (contains one proton and two neutrons) Another example is uranium-235, which has 92 protons and 143 neutrons, as opposed to uranium-238, which has 92 protons and 146 neutrons. An isotope is stable when it has a balanced number of neutrons and protons. In general, when an isotope is small and stable, it contains close to an equal number of protons and neutrons. Isotopes that are larger and stable have slightly more neutrons than protons. Examples of stable nuclides include carbon-12 (six protons and six neutrons for a total mass of 12), phosphorus-30 (15 protons and 15 neutrons) and sodium22 (11 protons and 11 neutrons). Radioisotopes Isotopes that are not stable and emit radiation are called radioisotopes. A radioisotope is an isotope of an element that undergoes spontaneous decay and emits radiation as it decays. During the decay process, it becomes less radioactive over time, eventually becoming stable. Once an atom reaches a stable configuration, it no longer gives off radiation. For this reason, radioactive sources – or sources that spontaneously emit energy in the form of ionizing radiation as a result of the decay of an unstable atom – become weaker with time. As more and more of the source’s unstable atoms become stable, less radiation is produced and the activity of the material decreases over time to zero. The time it takes for a radioisotope to decay to half of its starting activity is called the radiological half life, which is denoted by the symbol t½. Each radioisotope has a unique half-life, and it can range from a fraction of a second to billions of years. For example, iodine-131 has an eight-day half-life, whereas plutonium-239 has a half-life of 24,000 years. A radioisotope with a short half-life is more radioactive than a radioisotope with a long half-life, and therefore will give off more radiation during a given time period. There are three main types of radioactive decay: Alpha decay: Alpha decay occurs when the atom ejects a particle from the nucleus, which consists of two neutrons and two protons. When this happens, the atomic number decreases by 2 and the mass decreases by 4. Examples of alpha emitters include radium, radon, uranium and thorium. Beta decay: In basic beta decay, a neutron is turned into a proton and an electron is emitted from the nucleus. The atomic number increases by one, but the mass only decreases slightly. Examples of pure beta emitters include strontium-90, carbon-14, tritium and sulphur-35. Gamma decay: Gamma decay takes place when there is residual energy in the nucleus following alpha or beta decay, or after neutron capture (a type of nuclear reaction) in a nuclear reactor. The residual energy is released as a photon of gamma radiation. Gamma decay generally does not affect the mass or atomic number of a radioisotope. Examples of gamma emitters include iodine-131, cesium-137, cobalt-60, radium-226 and technetium-99m. The number of nuclear disintegrations in a radioactive material per unit time is called the activity. The activity is used as a measure of the amount of a radionuclide, and it is measured in becquerels (Bq). 1 Bq = 1 disintegration per second. If the original source of the radioactivity is known, it can be predicted how long it will take to decay to a given activity. The decay is exponential and the isotope must go through many half-lives to become nonradioactive. Figure 4 depicts the radioactive decay curve of carbon-14, which has a half-life of about 5,700 years. Even after a radioisotope with a high activity has decayed for several half-lives, the level of remaining radioactivity is not necessarily safe. Measurements of a radioactive material’s activity are always needed to estimate potential radiation doses. Types and Sources of Radiation Radiation is energy in the form of waves of particles. There are two forms of radiation – non-ionizing and ionizing. Non-ionizing radiation Non-ionizing radiation has less energy than ionizing radiation; it does not possess enough energy to produce ions. Examples of non-ionizing radiation are visible light, infrared, radio waves, microwaves, and sunlight. Global positioning systems, cellular telephones, television stations, FM and AM radio, baby monitors, cordless phones, garage-door openers, and ham radios use non-ionizing radiation. Other forms include the earth’s magnetic field, as well as magnetic field exposure from proximity to transmission lines, household wiring and electric appliances. These are defined as extremely low-frequency (ELF) waves and are not considered to pose a health risk. Ionizing radiation Ionizing radiation is capable of knocking electrons out of their orbits around atoms, upsetting the electron/proton balance and giving the atom a positive charge. Electrically charged molecules and atoms are called ions. Ionizing radiation includes the radiation that comes from both natural and man-made radioactive materials. There are several types of ionizing radiation: Alpha radiation (α) Alpha radiation consists of alpha particles that are made up of two protons and two neutrons each and that carry a double positive charge. Due to their relatively large mass and charge, they have an extremely limited ability to penetrate matter. Alpha radiation can be stopped by a piece of paper or the dead outer layer of the skin. Consequently, alpha radiation from nuclear substances outside the body does not present a radiation hazard. However, when alpha-radiation-emitting nuclear substances are taken into the body (for example, by breathing them in or by ingesting them), the energy of the alpha radiation is completely absorbed into bodily tissues. For this reason, alpha radiation is only an internal hazard. An example of a nuclear substance that undergoes alpha decay is radon-222, which decays to polonium-218. Beta radiation (β) Beta radiation consists of charged particles that are ejected from an atom’s nucleus and that are physically identical to electrons. Beta particles generally have a negative charge, are very small and can penetrate more deeply than alpha particles. However, most beta radiation can be stopped by small amounts of shielding, such as sheets of plastic, glass or metal. When the source of radiation is outside the body, beta radiation with sufficient energy can penetrate the body’s dead outer layer of skin and deposit its energy within active skin cells. However, beta radiation is very limited in its ability to penetrate to deeper tissues and organs in the body. Beta-radiation-emitting nuclear substances can also be hazardous if taken into the body. An example of a nuclear substance that undergoes beta emission is tritium (hydrogen-3), which decays to helium-3. Photon radiation (gamma [γ] and X-ray) Photon radiation is electromagnetic radiation. There are two types of photon radiation of interest for the purpose of this document: gamma (γ) and X-ray. Gamma radiation consists of photons that originate from within the nucleus, and X-ray radiation consists of photons that originate from outside the nucleus, and are typically lower in energy than gamma radiation. Photon radiation can penetrate very deeply and sometimes can only be reduced in intensity by materials that are quite dense, such as lead or steel. In general, photon radiation can travel much greater distances than alpha or beta radiation, and it can penetrate bodily tissues and organs when the radiation source is outside the body. Photon radiation can also be hazardous if photon-emitting nuclear substances are taken into the body. An example of a nuclear substance that undergoes photon emission is cobalt-60, which decays to nickel-60. Neutron radiation (n) Apart from cosmic radiation, spontaneous fission is the only natural source of neutrons (n). A common source of neutrons is the nuclear reactor, in which the splitting of a uranium or plutonium nucleus is accompanied by the emission of neutrons. The neutrons emitted from one fission event can strike the nucleus of an adjacent atom and cause another fission event, inducing a chain reaction. The production of nuclear power is based upon this principle. All other sources of neutrons depend on reactions where a nucleus is bombarded with a certain type of radiation (such as photon radiation or alpha radiation), and where the resulting effect on the nucleus is the emission of a neutron. Neutrons are able to penetrate tissues and organs of the human body when the radiation source is outside the body. Neutrons can also be hazardous if neutron-emitting nuclear substances are deposited inside the body. Neutron radiation is best shielded or absorbed by materials that contain hydrogen atoms, such as paraffin wax and plastics. This is because neutrons and hydrogen atoms have similar atomic weights and readily undergo collisions between each other. Figure 5 summarizes the types of radiation discussed in this document, from higher-energy ionizing radiation to lower-energy non-ionizing radiation. Each radiation source differs in its ability to penetrate various materials, such as paper, skin, lead and water. Natural sources of ionizing radiation Radiation has always been present and is all around us in many forms (see Figure 6). Life has evolved in a world with significant levels of ionizing radiation, and our bodies have adapted to it. Many radioisotopes are naturally occurring, and originated during the formation of the solar system and through the interaction of cosmic rays with molecules in the atmosphere. Tritium is an example of a radioisotope formed by cosmic rays’ interaction with atmospheric molecules. Some radioisotopes (such as uranium and thorium) that were formed when our solar system was created have half-lives of billions of years, and are still present in our environment. Background radiation is the ionizing radiation constantly present in the natural environment. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) identifies four major sources of public exposure to natural radiation: Cosmic radiation Terrestrial radiation Inhalation Ingestion Exposure from cosmic radiation The earth’s outer atmosphere is continually bombarded by cosmic radiation. Usually, cosmic radiation consists of fast moving particles that exist in space and originate from a variety of sources, including the sun and other celestial events in the universe. Cosmic rays are mostly protons but can be other particles or wave energy. Some ionizing radiation will penetrate the earth’s atmosphere and become absorbed by humans which results in natural radiation exposure. Exposure from terrestrial radiation The composition of the earth’s crust is a major source of natural radiation. The main contributors are natural deposits of uranium, potassium and thorium which, in the process of natural decay, will release small amounts of ionizing radiation. Uranium and thorium are found essentially everywhere. Traces of these minerals are also found in building materials so exposure to natural radiation can occur from indoors as well as outdoors. Exposure through inhalation Most of the variation in exposure to natural radiation results from inhalation of radioactive gases that are produced by radioactive minerals found in soil and bedrock. Radon is an odorless and colorless radioactive gas that is produced by the decay of uranium. Thoron is a radioactive gas produced by the decay of thorium. Radon and thoron levels vary considerably by location depending on the composition of soil and bedrock. Once released into the air, these gases will normally dilute to harmless levels in the atmosphere but sometimes they become trapped and accumulate inside buildings and are inhaled by occupants. Radon gas poses a health risk not only to uranium miners, but also to homeowners if it is left to collect in the home. On average, it is the largest source of natural radiation exposure. For more information on radon, read the CNSC’s Radon and Health document (INFO-0813) at nuclearsafety.gc.ca or visit Health Canada's Web site (hc-sc.gc.ca) to learn more about the means to control it in your home. Exposure through ingestion Trace amounts of radioactive minerals are naturally found in the contents of food and drinking water. For instance, vegetables are typically cultivated in soil and ground water which contains radioactive minerals. Once ingested, these minerals result in internal exposure to natural radiation. Naturally occurring radioactive isotopes, such as potassium-40 and carbon-14, have the same chemical and biological properties as their non-radioactive isotopes. These radioactive and non-radioactive elements are used in building and maintaining our bodies. Natural radioisotopes continually expose us to radiation and are commonly found in many foods, such as Brazil nuts. Table 1 identifies the amount of radioactivity from potassium-40 contained in about 500 grams of different food products. Several radioactive isotopes also occur naturally in the human body (see Table 2). Artificial (man-made) sources of ionizing radiation People are also exposed to man-made radiation from medical treatments and activities involving radioactive material. Radioisotopes are produced as a by-product of the operation of nuclear reactors, and by radioisotope generators like cyclotrons. Many man-made radioisotopes are used in the fields of nuclear medicine, biochemistry, the manufacturing industry and agriculture. The following are the most common sources: Medical sources: Radiation has many uses in medicine. The best-known application is in X-ray machines, which use radiation to find broken bones or to diagnose diseases. X-ray machines are regulated by authorities. Another example is nuclear medicine, which uses radioactive isotopes to diagnose and treat diseases such as cancer. A gamma camera (see Figure 7) is one piece of medical equipment commonly used in diagnosis. Industrial sources: Radiation has various industrial uses, which range from nuclear gauges (see Figure 8) used in the building of roads to density gauges that measure the flow of material through pipes in factories. Radioactive materials are also used in smoke detectors and some glow-in-the dark exit signs, as well as to estimate reserves in oil fields. Other applications include sterilization, which is performed using large, heavily shielded irradiators. Nuclear fuel cycle: Nuclear power plants (NPPs) use uranium to produce a chain reaction that produces steam, which in turn drives turbines to produce electricity. As part of their normal activities, NPPs release small quantities of radioactive material in a controlled manner to the surrounding environment. These releases are regulated to ensure doses to the public are well below regulatory limits. Uranium mines (see Figure 9), fuel fabrication plants and radioactive waste facilities are also licensed so the radioactivity they release (that can contribute to public dose) can be controlled by the authorities. Atmospheric testing: The atmospheric testing of atomic weapons from the end of the Second World War until as late as 1980 released radioactive material, called fallout, into the air. As the fallout settled to the ground, it was incorporated into the environment. Much of the fallout had short half-lives and no longer exists, but some continues to decay. People and the environment receive smaller and smaller doses from the fallout every year. Striking a balance Normally, there is little we can do to change or reduce ionizing radiation that comes from natural sources like the sun, soil or rocks. This kind of exposure, while never entirely free of risk, is generally quite low. However, in some cases, natural sources of radioactivity – such as radon gas in the home – may be unacceptably high and need to be reduced. The ionizing radiation that comes from man-made sources and activities is controlled more carefully. In these settings, a balance is struck between radiation’s societal benefits and the risks it poses to people, health and the environment. Dose limits are set to restrict radiation exposures to both workers and members of the public. In addition, licensees are required to keep all radiation doses as low as reasonably achievable (ALARA). There must also be a net benefit to support the use of radiation. For example, smoke detectors are permitted to use radioactive isotopes because smoke detectors save lives. Similarly, nuclear power plants provide us with electricity, while posing minimal risks that are carefully controlled. Health Effects of Radiation Exposure The word “safe” means different things to different people. For many, the idea of being safe is the absence of risk or harm. However, the reality is that almost everything we do presents a certain level of risk. For example, speed limits on roads are set to maximize safety. Nevertheless, accidents occur even when drivers obey the speed limit. Despite this risk, we still drive. Similar informed decisions are made when radiation is used. Radiation exposure carries a health risk. Understanding the risks helps the authorities and other regulatory bodies establish dose limits and regulations that keep exposure at an acceptable or tolerable risk level, where it is unlikely to cause harm. One significant advantage of radiation is that more is known about its associated health risks than about any other chemical or otherwise toxic agent. Since the early 20th century, radiation effects have been studied in depth, in both the laboratory and among human populations. Epidemiological evidence Studies on survivors of the atomic bombings of the cities of Hiroshima and Nagasaki in 1945 indicate that the principal long-term effect of radiation exposure is an increase in the frequency of cancer and leukemia. Similar results have been found in these groups: people who have been exposed to radiation through medical treatments or diagnostic procedures early uranium mine workers workers who manufactured atomic weapons people exposed to radiation as a result of the Chernobyl nuclear accident people exposed to radon gas in their homes Studies have shown that radiation will increase the frequency of some cancers that already occur naturally (or spontaneously), and that this increase is proportionate to the radiation dose; that is, the greater the dose, the greater the risk of cancer. These are referred to as stochastic effects (see section 4.3). However, studies to date have not shown that people chronically exposed to radiation at doses lower than about 100 millisieverts (mSv) 1 per year will experience an increase in cancer or other diseases. The following hypotheses attempt to explain why we cannot see radiation effects at doses of less than 100 mSv per year: One possible explanation is a dose threshold below which no cancers are caused; for example, radium has a threshold of 10 Sv for bone cancer. Another hypothesis is that the incidence of cancer caused by low radiation doses is so low that it cannot be distinguished from natural (or spontaneous) occurrences of the same cancer. This hypothesis is supported by studies of the National Academy of Biological Effects of Ionizing Radiation (BEIR), the French Academy of Sciences and the International Commission on Radiation Protection (ICRP). Scientists continue to try to detect the effects of low-dose radiation to support either of these potential explanations. Most people who showed health effects in studies were exposed to relatively high doses (greater than 100 mSv) delivered over a very short period of time. This is known as “acute” exposure. Normally, workers and members of the public exposed to radiation from the nuclear industry receive much lower doses over a considerably longer period of time (years as opposed to seconds). This is known as “chronic” exposure. Acute radiation exposure is estimated to be about 1.5 to 2 times more likely to produce health effects than chronic exposure. Cancer risk assessment The ICRP has calculated the probability of fatal cancer by relying primarily on the assessment of radiation effects by scientific bodies such as UNSCEAR and BEIR. It then determined what it calls the overall “detriment” of radiation exposure. This includes: the probability of fatal cancer the probability of non-fatal cancer the probability of severe hereditary effects the length of life lost if the harm occurs Using all these risks, the ICRP calculated an overall detriment of 0.042 (4.2%) per sievert for adult workers and 0.057 (5.7%) per sievert for the overall population (ICRP 103). The risk for the overall population is slightly higher than that of workers due to differences in certain variables, such as sex and age ranges, that were taken into account. The linear non-threshold model (LNT) is a risk model used internationally by most health agencies and nuclear regulators to set dose limits for workers and members of the public. The LNT conservatively assumes there is a direct relationship between radiation exposure and cancer rates. Several other risk models exist (see Figure 10), each with advantages and disadvantages. They differ depending on the basis of their assumptions and whether they take uncertainty into account. How radiation affects cells Radiation affects our health primarily through breakage of deoxyribonucleic acid (DNA) molecules. DNA is a long chain of amino acids whose pattern forms the blueprint on how a cell lives and functions, and radiation is able to break that chain. When it does, three things can happen: 1. The DNA is repaired properly: In this case, the cell is repaired properly and it continues to function normally. DNA breakage occurs normally every second of the day, and cells have a natural ability to repair that damage. 2. The DNA damage is so severe that the cell dies (deterministic effects): When the DNA or other critical parts of a cell receive a large dose of radiation, the cell may die or be damaged beyond repair. If this happens to a large number of cells in a tissue or organ, early radiation effects may occur. These early effects are called “deterministic effects” and their severity varies according to the radiation dose received. They can include burns, cataracts and, in extreme cases, death. The first evidence of deterministic effects became apparent with early experimenters and users of radiation. They suffered severe skin and hand damage due to excessive radiation exposure. More recently, such effects were observed during the 1986 Chernobyl nuclear plant accident where more than 130 workers and firefighters received high radiation doses (800 to 16,000 mSv) and suffered severe radiation sickness. Two of the people exposed died within days of exposure, and close to 30 more workers and firefighters died within the first three months. 3. The cell incorrectly repairs itself, but it continues to live (stochastic effects): In some cases, part of the DNA in the cell (see Figure 11) may be damaged by radiation and may not properly repair itself. The cell may continue to live and even reproduce itself. However, during that process, errors that have not been repaired in the DNA chain will also be present in the cell descendents and may disrupt these cells’ functioning. This type of detrimental effect has a probability that is proportionate to the dose, and is called a “stochastic effect.” With stochastic effects, the likelihood of effects increases as the dose increases. However, the timing of the effects or their severity does not depend on the dose. DNA damage happens continuously in the human body. People experience about 15,000 DNA damage events that do not result in cell death, every second of every day. After a cell is damaged, its structure can change due to improper repair; this alteration could have no further effect, or it could result in effects, such as cancer and hereditary effects, which show up later in life. If the DNA of sperm or egg cells is damaged, genetic damage occurs. This damage can result in a harmful characteristic that can be passed on from one generation to the next. Animal studies, such as those conducted on fruit flies by Hermann J. Muller in 1926, showed that radiation will cause genetic mutations. However, to date, genetic effects caused by radiation have not been observed in humans. This includes studies involving some 30,000 children of survivors of the atomic bombings of the Japanese cities of Hiroshima and Nagasaki, in 1945 (BEIR VII). Table 3 summarizes the potential health effects associated with given radiation doses. Dose limits have also been included to illustrate how they protect workers and the public. Radiation Doses For the purpose of radiation protection, dose quantities are expressed in three ways: absorbed, equivalent, and effective. Sections 5.1 to 5.3 describe these types of doses, respectively. Figure 12 presents an overview of the relationship between effective, equivalent and absorbed doses. Absorbed dose When ionizing radiation penetrates the human body or an object, it deposits energy. The energy absorbed from exposure to radiation is called an absorbed dose. The absorbed dose is measured in a unit called the gray (Gy). A dose of one gray is equivalent to a unit of energy (joule) deposited in a kilogram of a substance. Equivalent dose When radiation is absorbed in living matter, a biological effect may be observed. However, equal absorbed doses will not necessarily produce equal biological effects. The effect depends on the type of radiation (e.g., alpha, beta or gamma). For example, 1 Gy of alpha radiation is more harmful to a given tissue than 1 Gy of beta radiation. To obtain the equivalent dose, the absorbed dose is multiplied by a specified radiation weighting factor (wR). A radiation weighting factor (wR) is used to equate different types of radiation with different biological effectiveness. The equivalent dose is expressed in a measure called the sievert (Sv). This means that 1 Sv of alpha radiation will have the same biological effect as 1 Sv of beta radiation. In other words, the equivalent dose provides a single unit that accounts for the degree of harm that different types of radiation would cause to the same tissue. Effective dose Different tissues and organs have different radiation sensitivities (see Figure 13). For example, bone marrow is much more radiosensitive than muscle or nerve tissue. To obtain an indication of how exposure can affect overall health, the equivalent dose is multiplied by a tissue weighting factor (wT) related to the risk for a particular tissue or organ. This multiplication provides the effective dose absorbed by the body. The unit used for effective dose is also the sievert. For example, if someone’s stomach and bladder are exposed separately to radiation, and the equivalent doses to the organs are 100 and 70 mSv respectively, the effective dose is: (100 mSv x 0.12) + (70 x 0.05) = 15.5 mSv. The risk of harmful effects from this radiation would be equal to a 15.5 mSv dose delivered uniformly throughout the whole body. Natural radiation The total worldwide average effective dose from natural radiation is approximately 2.4 mSv per year. Cosmic radiation: Regions at higher altitudes receive more cosmic radiation. Terrestrial radiation: There are also natural sources of radiation in the ground, and some regions receive more terrestrial radiation from soils that contain greater quantities of uranium. The average effective dose from the radiation emitted from the soil (and the construction materials that come from the ground) is approximately 0.5 mSv per year. However, this dose varies depending on location and geology, with doses reaching as high as 260 mSv in Northern Iran or 90 mSv in Nigeria. In Canada, the estimated highest annual dose is approximately 2.3 mSv, as measured in the Northwest Territories. Inhalation: The earth’s crust produces radon gas, which is present in the air we breathe. Radon has four decay products that will irradiate the lungs if inhaled. The worldwide average annual effective dose of radon radiation is approximately 1.3 mSv. Ingestion: Natural radiation from many sources enters our bodies through the food we eat, the air we breathe and the water we drink. Potassium-40 is the main source of internal irradiation (aside from radon decay). The average effective dose from these sources is approximately 0.3 mSv a year. Man-made sources Man-made sources of radiation (from commercial and industrial activities) account for approximately 0.2 μSv of our annual radiation exposure. X-rays and other diagnostic and therapeutic medical procedures (see Table 5) account for approximately 1.2 mSv a year (UNSCEAR 2000). Consumer products like tobacco and smoke detectors account for another 0.1 mSv of our exposure to radiation each year. Overall, natural radiation accounts for approximately 60% of our annual radiation dose, with medical procedures accounting for the remaining 40%. There is no difference between the effects caused by natural or man-made radiation. Dose Limits For people who operate or work with nuclear energy, the regulated dose limit is set below the lower boundary of what is considered unacceptable exposure. For example, effective dose limits for nuclear energy workers are 50 mSv per year and 100 mSv over 5 years. Radiation exposures below an acute dose of approximately 100 mSv have not been shown to increase the risk of health effects such as cancer. References: “Electronics Waste Management in the United States Through 2009,” U.S. EPA, May 2011, EPA 530-R-11-002 “Municipal Solid Waste in the United States: 2011 Facts and Figures,” US EPA, May 2013, pages 67-72. Press Release, “Basel Conference Addresses Electronic Wastes Challenge.” November 27, 2006, United Nations Environment Programme (UNEP). 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National Council on Radiation Protection and Measurements (NCRP), Ionizing Radiation Exposure of the Population of the United States, NCRP Report No. 160 U.S. NCRP, Washington D.C. 2009. PhD in Engineering Management 2nd SEM AY 2013-2014 Nueva Ecija University of Science and Technology Graduate School