Organic Pollutants and Health Problems
Organic pollutants in drinking water seldom exceed trace concentrations: a few parts per billion (ppb) or even a few parts per trillion (ppt). These levels can be likened to 1 teaspoon of liquid creamer in 1,321,000 gallons of coffee (1 ppb) or in 1,321,000,000 gallons (1 ppt). Determining the health effect of pollutants present at such low levels is extremely difficult.
Toxicity is the inherent ability to impair health. Toxic substances can cause cancer, birth defects, and other illnesses. The severity of the effect usually depends on the dose, defined as the weight of the contaminant consumed per day divided by body weight. Dosages are usually measured in milligrams per kilogram of body weight per day. Acute toxicity refers to a contaminant’s ability to cause immediately detectable health problems. Chronic toxicity refers to a contaminant’s ability to cause health problems years after a long-term exposure. Keep in mind that some contaminants that cause no detectable health problems at low doses can cause death at high doses.
Nonlethal acute toxicity is easier to diagnose and treat than chronic toxicity since the ensuing health problems are generally brief and reversible. When the exposure to the chemical ceases, so do the effects, provided that the dosage has not been too high. Examples of organic chemicals that can be acutely toxic are the polychlorinated and polybrominated biphenyls (PCBs and PBBs)—a group of chemicals used in paints, electrical transformers, insulators, and the pesticides aldicarb, paraquat, and DDT. Symptoms of acute toxicity can include diarrhea, nausea, convulsions, blurred vision, and difficulty in breathing.
Health problems from chronic toxicity are more difficult to diagnose because they often remain latent for years. Once such problems become manifest, they may be difficult or impossible to treat. These complications make chronic toxicity from organic pollutants the major concern of those investigating water quality. Depending on the chronic health problems they cause, pollutants are typically grouped in the following three classes: carcinogens, mutagens, and teratogens.
Any chemical that causes cancer, either directly or indirectly, is a carcinogen. Although carcinogenesis receives more research attention than any other chronic effect, scientists have not determined the precise relationship between carcinogens and cancer. They do know, however, that carcinogens stimulate various forms of malignant tumors.
Fewer than 30 agents have been directly linked to human cancer. In contrast, nearly 1,500 are reported as being carcinogenic in animal tests, although this number includes results from studies whose experimental designs were questionable. Only about 7,000 of the over 5 million known substances have been tested for carcinogenicity.
Among the chemicals designated as causing cancer are vinyl chloride, a component of some resins; benzene, a solvent produced in petroleum refining; and benzo(a)pyrene, which results from the incomplete combustion of coal, kerosene, and shale. Benzo(a)pyrene also results from grilling foods. Numerous other chemicals are known to produce cancer in animals; they include the pesticides ethylene dibromide (EDB), kepone, heptachlor, and dieldrin.
A chemical capable of producing an inheritable change in the genetic material is called a mutagen. We know little about the mutagenic effects of organic chemicals because most suspected mutagens have been tested only on microorganisms and animals. Chemicals found to be mutagenic on the basis of such tests include vinyl chloride, benzo(a) pyrene, bromoform, chlorodibromomethane, and the fungicides Folpet and Captan.
Any chemical that produces a birth defect is called a teratogen. True understanding of teratogens is very limited. Some of the chemicals shown to have teratogenic effects in animals are nicotine and the pesticides 2,4-D; ‘2,4,5-T; and folpet. It is important to realize, however, that studies using laboratory animals and extremely high exposure rates are not always accurate predictors of human teratogens. This fact is often overlooked and can lead to misunderstandings.
Besides the health problems discussed above, organic pollutants may also cause arteriosclerosis, heart diseases, hypertension, emphysema, bronchitis, and kidney and liver dysfunction. Some evidence also links certain organic chemicals to metabolic disorders that stimulate abnormal production of enzymes.
Health Effects of Selected Drinking Water Contaminants
|CONTAMINANT||PROBABLE HEALTH EFFECTS*|
|Arsenic||Malignant tumors of skin and lungs, cramps, spasms, effects to nervous system|
|Barium||Prolonged stimulant action on muscles, nerve block|
|Benzene||Associated with cancer, leukemia, anemia|
|Cadmium||Bronchitis, anemia, gastrointestinal upsets, cancer in rats|
|Carbon tetrachloride||Central nervous system depression, gastrointestinal effects, liver and kidney damage, coma, death|
|Chlordane*||Carcinogen, liver and kidney damage|
|Chlorobenzene||Irritation to respiratory system, central nervous system depression|
|Chloroform||Possible liver, kidney and heart effects; carcinogenic in at least one animal species|
|Chromium||Kidney damage, cancer|
|Copper||Gastrointestinal tract irritant, possible infant fatality, Wilson’s disease|
|1,1-Dichloroethane||Central nervous system depression, liver damage, suggested animal carcinogen|
|1,2-Dichloroethane||Nausea, mental confusion, liver and kidney damage|
|Ethylenedibromide (EDS)||Decreased fertility|
|Fluoride||Skeletal damage when present in high levels|
|Heptachlor||Possible tumor induction, carcinogenic in test animals|
|Lead||Damage to nervous system, kidneys, reproductive system; cancer in rats|
|Lindane||Chronic liver damage, anemia, leukemia|
|Mercury||Kidney impairment, possible death|
|Nickel||Signs of hyperglycemia and gastrointestinal and nervous disorders|
|Pentachlorophenol (PCP)||Loss of appetite, respiratory difficulties, anesthesia, coma, death|
|PCBs||Damage to skin and liver; nausea, loss of weight, jaundice, coma, death|
|Selenium||Carcinogen; irritation to mucous membranes, dermatitis|
|Tetrachloroethylene||Central nervous system effects; confirmed animal carcinogen, anesthesia, death|
|Toluene||Narcosis, irritation to eyes and respiratory system|
|Toxaphene||Possible liver damage|
|1,1,1-Trichloroethane||Narcosis, depression of central nervous system, unconsciousness, death|
|1,1,2-Trichloroethane||Possible liver and kidney effects, possible carcinogen in animals|
|Trichloroethylene||Central nervous system depression, loss of coordination, unconsciousness; strong irritant and carcinogen|
|Trihalomethanes (THM’s)||Effects to nervous system and muscles, loss of consciousness|
|Vinyl chloride||Central nervous system depression, dulling of visual and auditory responses, possible death|
|Xylene||Mucous membrane irritant, lung congestion, impairment of kidney functions|
|Zinc||Muscular stiffness and pain, loss of appetite, nausea|