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Organic Pollutants in GroundwaterAuthor: M.P. Rao and P.S.C. Rao Organic Pollutants in Groundwater: 1. Health EffectsM.P. Rao and P.S.C. Rao In the early '60s and '70s, a considerable effort was expended in protecting and cleaning our surface waters, where the problems of contamination were readily visible. With recent widespread reports of trace quantities of organic pollutants being detected in drinking-water supplies, public attention and regulatory focus has shifted from surface water (lakes and rivers) to groundwater protection. Groundwater contamination has been called the problem of the '80s. What Are Organic Pollutants?Organic pollutants are chemicals that are made up primarily of carbon and hydrogen atoms and smaller amounts of various other atoms such as chlorine, nitrogen, sulfur, and phosphorus. There are over 70,000 chemicals in commercial use. The U.S. Environmental Protection Agency (EPA) has designated 654 of these chemicals as being hazardous. Florida's Department of Environmental Regulation (DER) reported that all of these chemicals are used in Florida.
Image by David Woodfall http://www.stillpictures.com/ Among the organic pollutants detected in groundwater are pesticides, solvents, degreasers, petroleum components, and various by-products of industrial manufacturing. A number of inorganic pollutants, such as fertilizers (nitrates), salts (chlorides), and heavy metals (lead, copper, etc.) as well as pathogens (viruses and bacteria) have also been detected in groundwater. The health effects from exposure to these chemicals and the methods to clean water contaminated by them have been discussed in References 3 and 4. In this fact sheet, we will discuss only the health risks associated with organic pollutants. What Is Groundwater?Groundwater, simply stated, is the water which is located underground, below the earth's surface. Water in soils and other geologic formations is stored in a complex network of pores and voids between the solid matrix, which consists of clays, sand, gravel, fissured rocks, and other similar materials. Closer to the ground surface, in a region called the unsaturated zone or the vadose zone, both water and air occupy the pores and voids. At deeper depths, in a region known as the saturated zone, water completely fills all the pore spaces. It is the water in this zone that we refer to as groundwater. The upper limit of the saturated zone is commonly referred to as the water table, and may occur at depths varying from a few feet to several hundred feet below ground surface. When the area of the saturated zone is large, and the ability of these zones to transmit water (i.e., their permeability) is sufficiently great to yield water to springs, rivers, and wells, they are referred to as aquifers. Further discussions on the various types of aquifers may be found in References 2 and 8. More than 50 percent of the nation's drinking water supply and about 80 percent of its rural domestic and livestock water needs are supplied by groundwater. According to the U.S. Geological Survey (USGS), groundwater usage in the U.S. was about 35 billion gallons per day in 1950 and is expected to increase to nearly 100 billion gallons per day by the late '80s. About 90 percent of Florida's population depends upon groundwater for its drinking water. A vast aquifer called the Floridan, which underlies portions of southern Alabama and Georgia and all of Florida, is a major source of drinking water in Florida. Based on the groundwater usage in the U.S., Florida ranks eighth in total freshwater withdrawal; first in rural, domestic, and livestock uses; second for public supply; third for industrial uses; and ninth for irrigation usage. Groundwater is not stagnant, but moves slowly at rates ranging from several feet to several hundred feet per year, depending upon the local hydrogeologic conditions. The natural quality of groundwater also varies considerably. Our discussion here is focused on groundwater that is potable, i.e., that which is of sufficiently high quality for human consumption. How Organic Pollutants Contaminate GroundwaterOrganic pollutants can enter groundwater in a number of ways. Pesticides applied to agricultural lands, forests, recreational areas (e.g., golf courses) and home lawns or gardens can leach through the soil and eventually contaminate the aquifer. A detailed discussion of factors that control the behavior of pesticides in soils, and which, in turn, determine the potential for pesticides to contaminate groundwater, is presented in Reference 5. Municipal landfills, leaking underground storage tanks, and poorly designed septic tank systems could also contribute to contamination of an aquifer. Industrial manufacturing wastes dumped legally or illegally could pollute groundwater. Numerous such incidents, including the infamous Love Canal site in New York state, have been documented in public media. Injection wells used for disposing liquid wastes in deep saline aquifers (containing salt-laden non-potable water and usually located below potable water aquifers and separated by a thick impermeable clay lens) could also leak pollutants. Health Effects Of Organic PollutantsWhile the health effects of consuming water contaminated by pathogens and nitrates are well known, the effects of exposure to organic pollutants are beginning to be understood only now. For the most part, we are interested in health effects associated with trace concentrations, a few parts per billion (ppb, µg,/liter) or even a few parts per trillion (ppt, ng/1iter), of organic pollutants in drinking water. Toxicity of an organic pollutant is defined as its inherent ability to cause an adverse health effect, such as the ability to induce cancer, birth defects and other illnesses in animals and humans. The severity of health effects from exposure to organic pollutants is dependent upon the dose (i.e., the magnitude and duration of exposure). For certain chemicals adverse health effects may not be observable at low doses, while death may result from high enough doses. These dose-response relationships are explored in Reference 1. The short-term toxicity of a chemical, manifested over a period of hours or days, is referred to as its acute toxicity. On the other hand, the long-term toxicity, observed after several years of exposure to a chemical, is known as the chronic toxicity. Acute toxicity is easier to diagnose and treat because the health effects are exhibited over a short period of time and, after exposure to low doses, these effects are usually reversible; that is, when the exposure to the chemical ceases, so do the effects. Among the many organic chemicals that exhibit acute toxicity are: polychlorinated and polybrominated biphenyls (PCBs and PBBs), a group of chemicals that are used in paints, electrical transformers, and insulators; and the pesticides aldicarb, paraquat, and DDT. Some of the acute effects from exposure to low doses of these compounds include diarrhea, nausea, respiratory distress, vomiting, convulsions, and blurred vision. Chronic toxicity is more difficult to diagnose and to treat because in some cases its effects are latent, taking several years before the adverse health effects become evident and by then it may be too late to reverse or terminate the adverse effects. Because of the uncertainty of affliction and the protracted effects, it is the chronic toxicity of organic pollutants in drinking water that is the major concern of scientists and the public. On the basis of their chronic toxic effects, organic chemicals may be grouped into the following three major classes: carcinogens, mutagens, and teratogens. Any chemical that causes cancer in either a direct or an indirect form is called a carcinogen. Although carcinogenesis is the most studied of all chronic effects, it is not entirely clear as to how carcinogens cause cancer. It is known, however, that these chemicals cause or stimulate the formation of malignant tumors of various forms in many parts of the body. Fewer than 30 agents are definitely linked to cancer in humans. In contrast, nearly 1,500 agents are reported as being carcinogenic in animal tests, although this number includes the results from studies with questionable experimental design. Only about 7,000 of the over 5 million known substances have been even tested for carcinogenicity. Among the chemicals suspected to produce carcinogenic effects in humans are: vinyl chloride, a component of some resins used in construction; benzene, a product of petroleum refining and used as a solvent; and benzo(a)pyrene, a constituent of coal, kerosene, and shale, as well as a naturally occurring chemical in many raw and cooked foods. Numerous other chemicals, including the pesticides ethylene dibromide (EDB), kepone, heptachlor, and dieldrin, are known to produce cancer in animals. 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. Most of the chemicals suspected to be mutagenic have only been tested using microorganisms and animals. Chemicals that have been found to be mutagenic include: vinyl chloride; benzo(a)pyrene; bromoform; chlorodibromomethane; and the fungicides folpet and captan. Any chemical that acts during pregnancy to produce a physical or functional defect in the developing offspring is known as a teratogen. Scientific knowledge on teratogens is very limited. Some of the chemicals that have been shown to have teratogenic effects in animals are: nicotine, found in cigarettes; and the pesticides 2,4-D, 2,4,5-T, and folpet. It is important to recognize that studies based only on animal species are not always accurate in determining human teratogens. Besides the major types of health effects discussed above, there are other effects. They include: arteriosclerosis; various forms of heart diseases; hypertension; emphysema; bronchitis; kidney and liver dysfunction; and diabetes. There is some evidence which links certain organic chemicals to metabolic disorders that stimulate abnormal production of enzymes. SummaryPublic concerns over health effects of consuming water contaminated by trace amounts of various organic chemicals have risen as reports of groundwater contamination have increased. Many of the organic chemicals detected in groundwater are known to be toxic. The possible adverse health effects of these chemicals have been briefly discussed in this fact sheet. In a following fact sheet (Reference 1), we discuss methods used to evaluate the health risks associated with consuming contaminated groundwater. References Cited & Further Reading
Footnotes1. This document is Fact Sheet SL-54, one of a series of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date first printed: March 1988. Reviewed: October 1997. Please visit the FAIRS Web site at http://hammock.ifas.ufl.edu. 2. M.P. Rao, student assistant; P.S.C. Rao, Professor; Soil and Water Science Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service. Copyright InformationThis document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.
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