Environmental Toxicology


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Environmental Toxicology

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Environmental Toxicology

  1. 1. Environmental Toxicology Unit-VII
  2. 2. Syllabus • Environmental risk assessment solid and hazardous waste management rules, hazardous waste control and remediation, evaluation of toxicity, toxic materials : their physiological and metabolic effects
  3. 3. Environmental Toxicology • Environmental Toxicology, is a multi- disciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms.
  4. 4. Environmental Toxicology • Rachel Carson is considered the mother of environmental toxicology, as she made it a distinct field within toxicology in 1962 with the publication of her book Silent Spring, which covered the effects of uncontrolled pesticide use. • Rachel Louise Carson (May 27, 1907 – April 14, 1964) was an American marine biologist and conservationist whose book Silent Spring and other writings are credited with advancing the global environmental movement.
  5. 5. Rachel Louise Carson
  6. 6. “Silent Spring” • Late in the 1950s, Carson turned her attention to conservation, especially environmental problems that she believed were caused by synthetic pesticides. The result was Silent Spring (1962), which brought environmental concerns to an unprecedented share of the American people. Although Silent Spring was met with fierce opposition by chemical companies, it spurred a reversal in national pesticide policy, which led to a nationwide ban on DDT and other pesticides, and it inspired a grassroots environmental movement that led to the creation of the U.S. Environmental Protection Agency. Carson was posthumously awarded the Presidential Medal of Freedom by Jimmy Carter.
  7. 7. “Silent Spring”
  8. 8. Agent Orange Vietnam War
  9. 9. Agent Orange Vietnam War • During the Vietnam War, between 1962 and 1971, the United States military sprayed nearly 20,000,000 U.S. gallons (75,700,000 l) of chemical herbicides and defoliants in Vietnam, the goal was to defoliate rural/forested land, depriving guerrillas of food and cover and clearing sensitive areas such as around base perimeters. The program was also a part of a general policy of forced draft urbanization, which aimed to destroy the ability of peasants to support themselves in the countryside, forcing them to flee to the U.S. dominated cities, depriving the guerrillas of their rural support base.
  10. 10. Agent Orange Vietnam War
  11. 11. Effects on the Vietnamese People Health Effects • The Vietnam Red Cross reported as many as 3 million Vietnamese people have been affected by Agent Orange, including at least 150,000 children born with birth defects. According to Vietnamese Ministry of Foreign Affairs, 4.8 million Vietnamese people were exposed to Agent Orange, resulting in 4,00,000 people being killed or maimed, and 5,00,000 children born with birth defects.
  12. 12. Effects on the Vietnamese People
  13. 13. Environmental Toxicology • Environmental Toxicology, is a multi-disciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms.
  14. 14. Environmental Toxicology • Harmful effects of chemical and biological agents can include toxins from pollutants, insecticides, pesticides, and fertilizers all of which can impact an organism and its community through shifts in species diversity and abundance. • Resulting changes in population dynamics impact the ecosystem by altering its productivity and stability.
  15. 15. Environmental Toxicology
  16. 16. Environmental Toxicology • There are many sources of environmental toxicity that can lead to the presence of toxins in our food, water and air. • These sources include organic and inorganic pollutants, pesticides and biological agents, all of which can have harmful effects on living organisms.
  17. 17. Environmental Toxicology
  18. 18. Environmental Toxicology • Pollutants Polychlorinated Biphenyls (PCBs) are organic pollutants that are still present in our environment today despite being banned in many countries such as the United States and Canada. Due to the persistent nature of PCBs in aquatic ecosystems, many aquatic species contain high levels of this chemical. • For example, fish farmed salmon have been shown to have significantly higher PCB levels.
  19. 19. Environmental Toxicology
  20. 20. Pollutants Polychlorinated Biphenyls (PCBs)
  21. 21. Environmental Toxicology Heavy Metals • Heavy metals found in food sources, such as fish can also have harmful effects. These metals can include mercury, lead, aluminum and cadmium. It has been shown that fish are exposed to higher cadmium levels and grow at a slower rate than fish exposed to lower levels or none.
  22. 22. Heavy Metals
  23. 23. Environmental Toxicology Pesticides • Pesticides are a major source of environmental toxicity. These chemically synthesized agents have been known to persist in the environment long after their administration. The poor bio-degradability of pesticides can result in bio-accumulation of chemicals in various organisms along with bio-magnification within a food web. Pesticides can be categorized according to the pests they target. Insecticides are used to eliminate agricultural pests that attack various fruits and crops. • Herbicides target herbal pests such as weeds and other unwanted plants that reduce crop production.
  24. 24. Pesticides
  25. 25. Pesticides
  26. 26. Environmental Toxicology Insecticides • Dichlorodiphenyltrichloroethane (DDT) is an organochlorine insecticide that has been banned due to its adverse effects on both humans and wildlife. DDT was widely used by farmers in order to kill agricultural pests. In 1962, the harmful effects of the widespread and uncontrolled use of DDT were detailed by Rachel Carson in her book The Silent Spring. Such large quantities of DDT and its metabolite Dichlorodiphenyldichloroethylene (DDE) that were released into the environment were toxic to both animals and humans
  27. 27. Dichlorodiphenyltrichloroethane (DDT)
  28. 28. Environmental Toxicology • DDT is not easily biodegradable and thus the chemical accumulates in soil and sediment runoff. Water systems become polluted and marine life such as fish and shellfish accumulate DDT in their tissues. Furthermore, this effect is amplified when animals who consume the fish also consume the chemical, demonstrating bio- magnification within the food web. • The process of bio-magnification has detrimental effects on various bird species. Rapid declines in bird populations have been seen various parts of the world.
  29. 29. Environmental Toxicology
  30. 30. Environmental Risk Assessment Solid and Hazardous Waste Management Rules • Hazardous wastes are considered highly toxic and therefore disposal of such wastes needs proper attention so as to reduce possible environmental hazards. • Industrial growth has resulted in generation of huge volume of hazardous wastes in the country. In addition to this, hazardous wastes sometimes get imported mainly from the western countries for re-processing or recycling. • Inventorisation of hazardous wastes generating units in the country is not yet Completed. Scientific disposal of hazardous wastes has become a major environmental issue in India.
  31. 31. Hazardous Wastes
  32. 32. Environmental Risk Assessment Solid and Hazardous Waste Management Rules • Hazardous Wastes (Management and Handling) Rules, 1989 have been framed by the Central Government and amended in 2000 and 2003 to deal with the hazardous wastes related environmental problems that may arise in the near future
  33. 33. Environmental Risk Assessment Solid and Hazardous Waste Management Rules
  34. 34. Environmental Risk Assessment Solid and Hazardous Waste Management Rules
  35. 35. Environmental Risk Assessment Solid and Hazardous Waste Management Rules • Environmental management of hazardous wastes has become a major concern in India as haphazard dumping of hazardous wastes results in severe environmental impairment. • The adverse effects of hazardous wastes as well as the significant potential risks posed by them to the life and its supporting systems are increasingly recognized Rapid growth of industries in India has resulted in generation of increasing volume of hazardous wastes. Both indigenously generated and imported from other countries for recycling or reprocessing need scientific treatment and disposal. However, only a few secured landfill sites are available in the country for disposal of hazardous wastes in an environmentally sound manner.
  36. 36. Environmental Risk Assessment Solid and Hazardous Waste Management Rules
  37. 37. Environmental Risk Assessment Solid and Hazardous Waste Management Rules • An illegal dumping of hazardous wastes by the industries may cause severe environmental pollution. The Ministry of Environment and Forests (MoEF) has promulgated Hazardous Wastes (Management & Handling) Rules, 1989 and amended the same in 2000 and 2003 for proper management and handling of hazardous wastes in the country. These rules also deal with the ban for importing a few categories of hazardous wastes. India has also ratified the Basel Convention on trans- boundary movement of hazardous wastes in 1992, which is a significant tool for controlling and monitoring of import and export of hazardous wastes and its proper management.
  38. 38. Illegal Dumping of Hazardous Wastes
  39. 39. Characteristics of Hazardous Wastes • Hazardous wastes, which may be in solid, liquid or gaseous form, may cause danger to health or environment, either alone or when in contact with other wastes . Hazardous wastes can be identified by the characteristics that they exhibit viz, ignitability, corrosivity, reactivity, or toxicity.
  40. 40. Characteristics of Hazardous Wastes
  41. 41. Characteristics of Hazardous Wastes
  42. 42. Characteristics of Hazardous Wastes Process Wastes • Hazardous wastes in India can be categorized broadly • into two categories, viz, • i) hazardous wastes generated in India from various industries, and • ii) hazardous wastes imported into or exported to India. Hazardous wastes are being generated in the country by various industries.
  43. 43. Characteristics of Hazardous Wastes
  44. 44. Characteristics of Hazardous Wastes • Inventorisation of hazardous wastes generating units and quantification of wastes generated in India are being done by the respective States. Pollution Control Boards (SPCBs) or Pollution Control Committees (PCCs). Depending on the physical and chemical characteristics of hazardous wastes, these may be categorized into three categories, viz. , recyclable, incinerable and landfill.
  45. 45. Characteristics of Hazardous Wastes
  46. 46. Characteristics of Hazardous Wastes
  47. 47. Characteristics of Hazardous Wastes • The hazardous wastes may be categorized as recyclable when resource recovery is possible by reprocessing the waste, as incinerable when it is possible to incinerate the wastes for destruction and energy recovery, and as landfill waste when this is not suitable either for resource or energy recovery, but suitable for dumping with or without any treatment.
  48. 48. Characteristics of Hazardous Wastes
  49. 49. Characteristics of Hazardous Wastes • Management and disposal The major issues of concern for hazardous wastes in India • Industrial incinerators in use are generally not efficient and are merely a combustion chamber and source of emission of dioxins and furans. Environmentally sound management of hazardous Wastes would require Common Hazardous Waste Management Facility (CHWMF) for industrial clusters spread all over the country, as it is not possible to have hazardous waste management facility for each unit, particularly in the case of small and medium scale units
  50. 50. Industrial Incinerators
  51. 51. Common Hazardous Waste Management Facility (CHWMF)
  52. 52. Health effects of Hazardous Wastes Health effects of hazardous wastes / substances • Hazardous wastes are considered very harmful to man and environment. These wastes pose a severe environmental hazard to the human health and to various components of environment, viz. soil, air or water Health impacts of hazardous pollutants have been studied in great detail by many organizations and individuals including the Government Organizations in India and other countries. In addition to research on health impacts, there are impact-related guidelines advocating for a full-fledged Health Impact Assessment (HIA) developed by several organizations
  53. 53. Health effects of Hazardous Wastes
  54. 54. Hazardous Wastes (Management and Handling) Rules, 1989 Hazardous Wastes (Management and Handling) Rules, 1989 • As amended to date, were notified in the country under the provisions of the Environment (Protection) Act, 1986, for management and handling, and import of hazardous wastes into the country. These rules were amended in 2000 and 2003, to bring the Rules in line with the requirements of the Basel Convention and also to improve the applicability and implementation aspects with regard to imports of hazardous waste.
  55. 55. Hazardous Wastes (Management and Handling) Rules, 1989
  56. 56. Hazardous Wastes (Management and Handling) Rules, 1989
  57. 57. Hazardous Wastes (Management and Handling) Rules, 1989 • Apart from Ministry of Environment and Forests (MoEF), Central Pollution Control Board (CPCB), State Pollution Control Boards (SPCBs) / Pollution Control Committees (PCCs) have been delegated certain powers for control and regulation of hazardous wastes
  58. 58. Recycling of Hazardous Wastes • Hazardous wastes having the resource values are recycled or reprocessed for value recovery. Used oil, battery wastes and other non ferrous wastes like zinc, lead are commonly recycled in India. • Used oil contains high levels of various heavy metals like lead, cadmium, arsenic and chromium etc. It also contains contaminants such as chlorinated solvents, polychlorinated bi-phenyls and other carcinogens.
  59. 59. Recycling of Hazardous Wastes
  60. 60. Recycling of Hazardous Wastes • It is estimated that one gallon of used oil is sufficient to contaminate one million gallons of ground water. Import of used oil/waste oil is banned in India due to its potential pollution hazard. However used oil is a precious and non-renewable resource and can be recycled back to pure lube oil again and again.
  61. 61. Recycling of Hazardous Wastes
  62. 62. Recycling of Hazardous Wastes
  63. 63. Electronic Wastes • Over the years, our dependence on the electronic products has grown manifold, both for domestic and for office uses, and this has resulted in generation of electronic wastes (E- waste) all over the world. • E-wastes are a fast growing waste stream. On an average, E-waste makes up approximately 1 percent of municipal solid waste (MSW) stream as per the study report of EPA.
  64. 64. Electronic Wastes
  65. 65. Electronic Wastes • These E-wastes contain hazardous substances, such as lead, mercury, chromium, etc. A television and CRT monitor contains about four pounds of lead on an average. E-waste may contribute high level of Hg Contamination in Municipal solid waste.
  66. 66. Electronic Wastes
  67. 67. Recycling of E-waste • Re-cycling of E-waste is a need of the day to reduce/ avoid pollution, and to extract valuable and limited resources. Recycling reduces the energy used in new product. Manufacturing. In developed countries, municipalities, public and private organizations accept used / waste computers and other electronics for recycling.
  68. 68. Recycling of E-waste
  69. 69. Recycling of E-waste • Now electronics manufacturers like Dell and HP are offering recycling services in some countries.
  70. 70. Legislations and Regulations for Hazardous Wastes • There are 36 types of industrial processes listed in Schedule-I of Hazardous Wastes (Management & Handling) Amendments Rule, 2003. • As per Rule 11 of the Hazardous Wastes Rules, 1989, import of hazardous wastes from any country to India shall not be permitted for dumping. Import of hazardous wastes
  71. 71. Legislations and Regulations for Hazardous Wastes • Import of hazardous wastes may be allowed for processing or re-use as raw material, after examining each case on merit by the Ministry of Environment & Forests. • In Schedule 8 of Hazardous Wastes Amendment Rules, 2003, 29 categories of hazardous wastes, prohibited for import and export. Wastes containing Hg, As, Waste Asbestos (Dust or Fibres), waste oil etc., are in the list of banned wastes for import and export.
  72. 72. Legislations and Regulations for Hazardous Wastes
  73. 73. Legislations and Regulations for Hazardous Wastes • Any person importing hazardous wastes shall maintain the records of the hazardous wastes imported as specified in Form 6A, and the records so maintained shall be open for inspection by the MoEF / CPCB / SPCB / PCC, or an officer designated by these regulatory bodies.
  74. 74. Legislations and Regulations for Hazardous Wastes • The Ministry of Environment and Forests (MoEF) is the nodal agency for environmental matters in India. It exercises control over imports of hazardous wastes under the Hazardous Wastes Rules. • Hazardous Substances Management Division (HSMD) of the MoEF deals with the management of hazardous wastes (both indigenous and imported), hazardous chemicals and major chemical accidents.
  75. 75. Legislations and Regulations for Hazardous Wastes
  76. 76. Basel Convention • Basel Convention deals with the trans-boundary movement and disposal of hazardous wastes as well as other chemical wastes by regulating and controlling the movement of scheduled hazardous wastes from OECD countries (Organisation for Economic Co-operation and Development) to non OECD countries. India ratified the convention in 1992 showing India's commitment to solve the problem of trans- boundary movement and disposal (or dumping) of hazardous wastes through international cooperation.
  77. 77. Basel Convention
  78. 78. Legislations and Regulations for Hazardous Wastes • It is difficult to develop alternative technology for total elimination of hazardous wastes generation. In developing countries, the thrust on economic development is often given priority to production costs than the best available technology and this results in more wastes generation. • The MoEF has elaborately identified various treatment and disposal options of different hazardous waste streams that include physical / chemical treatment, landfill, biological treatment, incineration, recycle and recovery and solidification etc. As on today, the most often used option for disposal of wastes is secured landfill.
  79. 79. Legislations and Regulations for Hazardous Wastes • The other options should be given also equal weightage to reuse and recycle of such wastes for resource recovery before deciding for a landfill. • Environmental Impact Assessment (EIA) is being practiced all over the world to decide a site of secured landfill to ensure less negative impact of such facility on human and ecological systems.
  80. 80. Legislations and Regulations for Hazardous Wastes
  81. 81. Toxicology • Toxicology can be defined as that branch of science that deals with “the detection, occurrence, properties, effects, and regulation of toxic substances,”
  82. 82. Toxicology
  83. 83. Routes of Exposure • There are four routes by which a substance can enter the body: inhalation, skin (or eye) absorption, ingestion, and injection. • Inhalation: For most chemicals in the form of vapours, gases, mists, or particulates, inhalation is the major route of entry. Once inhaled, chemicals are either exhaled or deposited in the respiratory tract. If deposited, damage can occur through direct contact with tissue or the chemical may diffuse into the blood through the lung-blood interface.
  84. 84. Routes of Exposure
  85. 85. Routes of Exposure • Upon contact with tissue in the upper respiratory tract or lungs, chemicals may cause health effects ranging from simple irritation to severe tissue destruction. Substances absorbed into the blood are circulated and distributed to organs that have an affinity for that particular chemical. Health effects can then occur in the organs, which are sensitive to the toxicant
  86. 86. Routes of Exposure • Skin (or eye) absorption: Skin (dermal) contact can cause effects that are relatively innocuous such as redness or mild dermatitis; more severe effects include destruction of skin tissue or other debilitating conditions. Many chemicals can also cross the skin barrier and be absorbed into the blood system. Once absorbed, they may produce systemic damage to internal organs. The eyes are particularly sensitive to chemicals. Even a short exposure can cause severe effects to the eyes or the substance can be absorbed through the eyes and be transported to other parts of the body causing harmful effects.
  87. 87. Routes of Exposure
  88. 88. Routes of Exposure • Ingestion: Chemicals that inadvertently get into the mouth and are swallowed do not generally harm the gastrointestinal tract itself unless they are irritating or corrosive. Chemicals that are insoluble in the fluids of the gastrointestinal tract (stomach, small, and large intestines) are generally excreted. Others that are soluble are absorbed through the lining of the gastrointestinal tract. They are then transported by the blood to internal organs where they can cause damage. • Injection: Substances may enter the body if the skin is penetrated or punctured by contaminated objects. Effects can then occur as the substance is circulated in the blood and deposited in the target organs.
  89. 89. Routes of Exposure
  90. 90. Routes of Exposure • Once the chemical is absorbed into the body, three other processes are possible: metabolism, storage, and excretion. Many chemicals are metabolized or transformed via chemical reactions in the body. In some cases, chemicals are distributed and stored in specific organs. • various excretory mechanisms (exhaled breath, perspiration, urine, faeces, or detoxification) rid the body, over a period of time, of the chemical. For some chemicals elimination may be a matter of days or months; for others, the elimination rate is so low that they may persist in the body for a lifetime and cause deleterious effects.
  91. 91. Health Effects • Human health effects caused by exposure to toxic substances fall into two categories: short-term and long-term effects. Short-term effects (or acute effects) have a relatively quick onset (usually minutes to days) after brief exposures to relatively high concentrations of material (acute exposures). The effect may be local or systemic.
  92. 92. Health Effects
  93. 93. Health Effects • Long-term effects (or chronic effects) are those with a long period of time (years) between exposure and injury. These effects may occur after apparent recovery from acute exposure or as a result of repeated exposures to low concentrations of materials over a period of years (chronic exposure). • Usually the major effects of a chemical will be expressed in one or two organs. These organs are known as target organs which are more sensitive to that particular chemical than other organs.
  94. 94. Respiratory Tract • Many chemicals used or produced in industry can produce acute or chronic diseases of the respiratory tract when they are inhaled .The toxicants can be classified according to how they affect the respiratory tract.
  95. 95. Respiratory Tract
  96. 96. Respiratory Tract • Asphyxiants: gases that deprive the body tissues of oxygen • Simple asphyxiants are physiologically inert gases that at high concentrations displace • air leading to suffocation. Examples: nitrogen, helium, methane, neon, argon. • Chemical asphyxiants are gases that prevent the tissues from getting enough oxygen. • Examples: carbon monoxide and cyanide.
  97. 97. Asphyxiants
  98. 98. Respiratory Tract • Irritants: chemicals that irritate the air passages. Examples: hydrogen fluoride, chlorine, hydrogen chloride, and ammonia. • Necrosis producers: Chemicals that result in cell death and edema. Examples: ozone and nitrogen dioxide. • Fibrosis producers: Chemicals that produce fibrotic tissue which, if massive, blocks airways and decreases lung capacity. Examples: silicates, asbestos, and beryllium.
  99. 99. Respiratory Tract
  100. 100. Respiratory Tract • Allergens: Chemicals that induce an allergic response. Examples: isocyanates and sulfur dioxide. • Carcinogens: Chemicals that are associated with lung cancer. Examples: cigarette smoke, coke oven emissions, asbestos, and arsenic.
  101. 101. Respiratory Tract
  102. 102. Skin • Skin. The skin is, in terms of weight, the largest single organ of the body. It provides a barrier between the environment and other organs (except the lungs and eyes) and is a defense against many chemicals. • The skin consists of the epidermis (outer layer) and the dermis (inner layer). In the dermis are sweat glands and ducts, sebaceous glands, connective tissue, fat, hair follicles, and blood vessels. • Hair follicles and sweat glands penetrate both the epidermis and dermis. Chemicals can penetrate through the sweat glands, sebaceous glands, or hair follicles.
  103. 103. Skin
  104. 104. Skin • The ability of skin to absorb foreign substances depends on the properties and health of the skin and the chemical properties of the substances. • Absorption of a toxic chemical through the skin can lead to local effects through direct contact, such as irritation and necrosis, and systemic effects. • Many chemicals can cause a reaction with the skin resulting in inflammation called dermatitis.
  105. 105. Skin These chemicals are divided into three categories: Primary irritants: Act directly on normal skin at the site of contact (if chemical is in sufficient quantity for a sufficient length of time). Skin irritants include: acetone, benzyl chloride, carbon disulfide, chloroform, chromic acid and other soluble chromium compounds, ethylene oxide, hydrogen chloride, iodine, methyl ethyl ketone, mercury, phenol, phosgene, styrene, sulfur dioxide, picric acid, toluene, xylene.
  106. 106. Primary Irritants
  107. 107. Skin • Photosensitizers: Increase in sensitivity to light, which results in irritation and redness. Photosensitizers include: tetracyclines, creosote, pyridine, furfural, and naphtha • Allergic sensitizers: May produce allergic-type reaction after repeated exposures. They include: formaldehyde, phthalic anhydride, ammonia, mercury, nitrobenzene, toluene diisocyanate, chromic acid and chromates, cobalt, and benzoyl peroxide.
  108. 108. Eyes • The eyes are affected by the same chemicals that affect skin, but the eyes are much more sensitive. • Acids: Damage to the eye by acids depends on pH and the protein-combining capacity of the acid. • Alkalies: Damage that appears mild initially but can later lead to ulceration, perforation, and clouding of the cornea or lens. • Organic solvents: Organic solvents (for example, ethanol, toluene, and acetone) dissolve fats, cause pain, and dull the cornea. Damage is usually slight unless the solvent is hot. • In addition, some compounds act on eye tissue to form cataracts, damage the optic nerve, or damage the retina.
  109. 109. Eyes
  110. 110. Central Nervous System. • Neurons (nerve cells) have a high metabolic rate but little capacity for anaerobic metabolism. Subsequently, inadequate oxygen flow (anoxia) to the brain kills cells within minutes. Some may die before oxygen or glucose transport stops completely.
  111. 111. Central Nervous System
  112. 112. Central Nervous System • Because of their need for oxygen, nerve cells are readily affected by both simple asphyxiants and chemical asphyxiants. Also, their ability to receive adequate oxygen is affected by compounds that reduce respiration and thus reduce oxygen content of the blood. Other examples are compounds such as arsine, nickel, ethylene chlorohydrins, tetraethyl lead, aniline, and benzene that reduce blood pressure or flow due to cardiac arrest, extreme hypotension, hemorrhaging.
  113. 113. Liver • Liver injury induced by chemicals has been known as a toxicological problem for hundreds of years. It was recognized early that liver injury is not a simple entity, but that the type of lesion depends on the chemical and duration of exposure.
  114. 114. Liver
  115. 115. Kidneys • A number of materials are toxic to the kidneys: • Heavy metals, may denature proteins as well as produce cell toxicity. Heavy metals (including mercury, arsenic, gold, cadmium, lead, and silver) are readily concentrated in the kidneys, making this organ particularly sensitive. • Halogenated organic compounds, which contain chlorine, fluorine, bromine, or iodine. • Metabolism of these compounds, like that occurring in the liver, generates toxic metabolites. Among compounds toxic to the kidneys are carbon tetrachloride, chloroform, 2,4,5-T (a herbicide), and ethylene dibromide (a fumigant).
  116. 116. Kidneys
  117. 117. Guidlines • Several reference sources are available that contain information about toxicological properties and safe exposure limits for many different materials. • However, because most of the data is for animal exposures, there may be problems in trying to use the data for human exposure guidelines.
  118. 118. Guidlines • Other sources give some general guides on chemical exposure. They may say that the chemical is an irritant or corrosive, or they may give a warning like "AVOID CONTACT" or "AVOID BREATHING VAPORS." This gives the user information about the possible route of exposure and effects of the exposure. However, this does not give a safe exposure limit. One may question whether the warning means to "AVOID ANY POSSIBLE CONTACT" or whether there is a certain amount that a person can contact safely for a certain length of time.
  119. 119. References Environmental Management Bala Krishnamoorthy- PHI publication Wikipedia- The online free Encyclopedia http://www.nioh.org/
  120. 120. “If we have no peace, it is because we have forgotten that we belong to each other.” ― Mother Teresa
  121. 121. Thanks….