Water from most sources contains at least some chemicals or other agents. Some of these agents are naturally occurring minerals, and water supplies are highly variable in their mineral contents. Naturally occurring minerals can include calcium, selenium, zinc, fluoride, magnesium, and others. Most drinking water contains mineral concentrations that are low enough that they do not adversely affect the health of most people and may actually provide some beneficial effect. For example, calcium and magnesium are important in bone health and other physiologic processes, and selenium is important in general antioxidant function and in immune system health. Several studies, but not all, have identified associations between increased water hardness (typically measured as calcium carbonate or calcium and magnesium concentrations) and lower rates of cardiovascular disease mortality. Some reports suggest the strongest evidence for this is for magnesium content. In some instances, minerals are intentionally added to water supplies in order to take advantage of their beneficial effects. An example of this is fluoride, which is sometimes intentionally added to water supplies to help prevent tooth caries. Desalination of seawater is becoming an increasing source of drinking water in several areas lacking abundant freshwater supplies, such as very dry areas in Israel and northern Chile. This process can result in substantial demineralization of the water and a subsequent loss of any beneficial effects of the minerals normally present in other water sources. Mixing desalinated water with source water or the addition of minerals is sometimes done to achieve a balanced mineral content in desalinized water.
Many water supplies contain toxic agents or toxic concentrations of agents that are otherwise benign at lower concentrations. Chemical contamination of water is a worldwide problem. Contaminant sources can either be man-madeor natural. An example of a naturally occurring toxic agent is arsenic, which is present in many water supplies worldwide and which has been linked to cancer and other adverse outcomes. Many contaminant sources are man-made and a result of industrial pollution. Figure 48–1 demonstrates many of the inputs and outputs of the water cycle. Agricultural chemicals, industrial chemicals, mining wastes, septic tank and landfill leakage, and direct sewage discharge to surface or groundwater may contaminate drinking water resources. This may either occur on a large scale or on a small scale. In Henderson, Nevada, waste materials containing perchlorate released from a single chemical manufacturing plant made their way into nearby soil and eventually formed a plume of material that slowly spread from its original source to nearby water systems. This single source eventually resulted in 1000 pounds of perchlorate per day entering Lake Mead and the Colorado River, which are major sources of drinking water for large parts of the southwest United States.
How waste-disposal practices can contaminate the groundwater system.
Smaller-scale backyard and garage contamination sources may be equally important. Although usually unrecognized and unreported, these releases will appear quite soon afterwards in the water supply of the local districts. Small-scale inputs of agricultural chemicals from domestic lawn and garden care with herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) can pollute large quantities of drinking water. In the early 1970s, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), a phenoxy herbicide closely related to 2,4-D, which was a component of Agent Orange, the defoliant used in Vietnam by American military forces, was deregistered for domestic lawn care purposes because of its potential to contaminate water in or around homes with materials that were believed teratogenic or embryotoxic to humans. Halogenated solvents, paints and varnishes, carburetor cleaners, and gasoline may become troublesome if released to the groundwater or surface waters in quantities below those that are regulated and reportable. These chemicals can be a significant source of local and regional surface and groundwater pollution.
Extensive contamination of water resources with persistent organic chemicals is a worldwide problem. The North American Great Lakes and many local rivers and streams have been heavily polluted with polychlorinated compounds. These compounds include the polychlorinated and polybrominated biphenyls used extensively in twentieth century industrial processes. Huge expenditures to remove and remediate these waters have been made, and more are underway. The ultimate removal of these materials from the environment will take many years. The problem is not confined to North America or western Europe.
Airborne particulate matter, which is produced by the combustion of fossil fuels, may carry high loads of oxides of sulfur. These sulfur compounds are either adsorbed to the particulate's core or are dissolved in the aerosols that oxidative combustion produces. Acid particulates contribute an acid load to atmospheric water, which may become acid precipitation. Because these acidic materials are quite stable in water, they progressively acidify the surface and groundwater into which they are mixed. Smokes, aerosols, mists, and vapors all may contribute organic materials and inorganic substances of varying toxicologic significance to the air. In the vicinity of some coal-fired power plants and some other solid or beneficiated fuel-fired facilities, alkaline fly ash is deposited, which produces paradoxical alkalinization of the soil and adjacent surface water and groundwater. Much of the particulate-bound load is partially water soluble. It will reprecipitate to the earth's surface as atmospheric conditions change and rain falls. Oxynitrogenated organics, partially soluble polynuclear organics, and metallo-organics may participate in the evaporation-precipitation cycle to contaminate surface and subsurface waters.
A phenomenon receiving more recent attention is the contamination of water sources with pharmaceutical products for humans or animals, as well as their related metabolites. Human sources include intentional flushing of medications down the toilet, rinsing topically applied medications off in the tub or sink, or excretion of medications in urine or feces. Most waste water treatment plants are not designed to remove these chemicals, and therefore they can pass through these treatment plants and eventually end up in downstream water sources. An example of this is Lindane. This is a topical treatment used to treat head lice and scabies and may cause skin irritation, dizziness, headaches, diarrhea, and other gastrointestinal symptoms at high exposures. Elevated levels of Lindane had been reported in the effluent of several large waste water treatments plants in the Los Angeles area. Fortunately, these levels were shown to decline after state laws were passed banning the pharmaceutical use of this agent. Little is known about the health effects of long-term exposure to low concentrations of pharmaceuticals to humans or aquatic organisms. The precautionary principle—or possibly new scientific evidence—may give rise to more stringent demands on waste water treatment in the future. A combination of biologic treatment with high sludge residence times and ozonation of the effluent seems to be the most promising technology to control pharmaceutical product contamination.
Surface water and groundwater contamination from industrial disposal practices was common in the United States until the passage of the Clean Water Act. Prior to that time, there was rampant disposal of many persistent organic compounds into surface and groundwater supplies. In recent years, dumping of agricultural and industrial chemicals has been greatly reduced. In the future, new major pollution problems may not occur as a result of deliberate disposal practices in the United States because of enforcement of this Act.
The right to discharge materials into the environment is granted under a permitting process that is administered by state, local, and federal authorities. The permits that are granted specify the quantities of pollutants that may be discharged, the conditions under which they may be discharged, and the time of discharge. They also establish the monitoring and other activities that must be carried out to ensure compliance with the permit. These National Pollutant Discharge Elimination System (NPDES) permits are designed to keep information flowing about environmental contamination. They help to ensure that a responsible standard is applied uniformly to all who discharge hazardous materials and who contaminate water resources, soil, or air.
Specific Chemical Contaminants
In the past, arsenic was used as an effective poison because it is odorless, tasteless, and clear in water, and at very high doses causes severe gastrointestinal symptoms, liver and kidney damage, hemolysis, and eventually death. Inorganic arsenic in water can occur in several valence states (eg, As(III) and As(V)), but this has little impact on human health since they are essentially interchangeable in the human body.
Tens of millions of people worldwide are exposed to arsenic in their drinking water, including an estimated 50 million in Bangladesh, 30 million in India, 15 million in China, and millions more in the United States, Europe, and South and Central America. Most of this arsenic is naturally occurring, although some industrial contamination also occurs. Although these exposures are orders of magnitude lower than those that can cause acute poisoning and rapid death, several important health effects of these lower exposures have been identified.
Perhaps most importantly, epidemiologic studies from large populations in Taiwan, Japan, Argentina, Chile, and elsewhere with naturally-occurring arsenic in their drinking water (eg, mostly 200–1000 μg/L) have identified associations between these exposures and increased rates of various cancers. The International Agency for Research on Cancer has classified ingested arsenic as cause of lung, bladder, skin, and possibly kidney cancer in humans. Arsenic is fairly unusual in the sense that it is the only chemical agent that causes lung cancer following ingestion. In fact, arsenic-caused lung cancer appears to be the most common cause of death related to ingested arsenic. It is also unusual in that appears to cause cancer in humans at much lower exposure levels than it does in laboratory animals. Pathognomonic lesions of arsenic include hyperkeratosis of the palms and soles of the feet and a hypo- and hyperpigmentation usually involving the chest, but these lesions typically only occur at very high exposures (>200 μg/L), and even then susceptibility to these lesions varies widely. Recent research has also linked arsenic exposures in water to ischemic heart disease; peripheral vascular disease including “blackfoot disease;” diabetes; chronic renal disease; nonmalignant lung disease including bronchiectasis, respiratory symptoms like cough and dyspnea, and diminishedpulmonary function; as well as reproductive and developmental effects in children including low birth weight, spontaneous abortion, and decreases in cognitive function. The risks of drinking arsenic contaminated water can be high. In a recent study, in Bangladesh, exposure to arsenic water concentrations higher than 150 μg/L was found to be associated with a 68% increase in overall mortality.
The current regulatory standard for arsenic in water in many countries and the WHO recommendation is 10 μg/L. Many countries do not follow or enforce this standard because of a lack of alternative water sources and the high cost of removing arsenic from water. Most ingested arsenic is excreted in the urine within 2 weeks of ingestion, and urinary concentrations of arsenic are the best metric for assessing exposure. Valid urine analysis should include inorganic arsenic and its major methylated metabolites, and exclude organic forms of arsenic which come predominantly from seafood and are mostly nontoxic. Most people receive some arsenic from foods such as rice, fruits, and vegetables, and urinary levels of inorganic arsenic and its metabolites in people without water contamination are usually less than 10 μg/L. Toenail and hair levels can also be measured but external contamination and wide interindividual variability can limit their usefulness. Treatment of arsenic exposure from water primarily involves removal from exposure. Chelation therapy may be used for massive acute arsenic toxicity but this is usually only reserved for very high (acute) exposures such as occupational accidents or accidental ingestions of arsenic pesticides in children. Chelation therapy has not been shown to reduce health outcomes in those with lower, more chronic and common drinking water exposures.
The chemical structure of perchlorate is ClO4−. It has been used industrially as an oxidizer in solid rocket propellant, slurry explosives, road flares, and air bag inflation systems. Human environmental exposure can occur through food or water following industrial contamination from industries that use or manufacture perchlorate (eg, Colorado River water) or from perchlorate that is naturally occurring (eg, northern Chile). In two recent nationally representative surveys in the United States, detectable concentrations of perchlorate were reported in the urine of every person tested suggesting that essentially everyone has at least some exposure to perchlorate.
High doses of perchlorate have been shown to competitively inhibit iodide uptake by the sodium iodide symporter in the thyroid gland. This effect is important since iodide is a key component of thyroid hormone, and blocking iodide uptake into the thyroid can decrease thyroid hormone production. In the past, perchlorate was used therapeutically to treat hyperthyroidism until safer alternatives were found. Concentrations of perchlorate in drinking water are typically orders of magnitude lower than those previously used to treat hyperthyroidism. However, several studies have reported links between perchlorate in drinking water and decreased thyroid hormone levels, especially in potentially susceptible groups such young children, those with low iodine intake, and those exposed to other agents that work by the same mechanism (eg, nitrate and thiocyanate), although these findings are not consistent across all studies.
The potential effects of perchlorate on the thyroid can have important public health implications since thyroid hormone plays a key role in many physiologic functions. In the fetus and child, thyroid hormone is critical for normal brain and neurologic development, and several studies have reported links between decreased thyroid hormone levels during pregnancy and the subsequent cognitive development and IQ of the offspring. The results of a few studies have suggested that these effects may even occur with very small decreases in thyroid hormone, and with decreases that occur within normal reference ranges. Some authors have suggested that perchlorate toxicity can be prevented by ensuring adequate iodine intake in exposed populations. However, this has not been confirmed and high iodine intake is also associated with some toxicity (eg, paradoxical hypothyroidism in some people).
Once ingested, perchlorate is generally not metabolized and is excreted in urine within a few days. Urinary levels of perchlorate are the best metric for assessing recent exposure. In populations without an obvious exposure source, urinary perchlorate concentrations are usually 5−10 μg/L.
Chromium (Cr) in the environment is present in several valence states but the ones considered the most biologically significant are Cr(III) and Cr(VI). Cr(III) is an essential nutrient found in dietary sources such as breads, cereals, and vegetables, while Cr(VI) is a carcinogen. Exposure to chromium can occur through inhalation, ingestion, or dermal absorption. Cr(VI) has been used in chrome plating, chromate dye production, textile production, leather tanning, Portland cement, stainless steel production and welding, wood treatment, and other industries. Chromium can also be released into the environment from the burning of natural gas, oil, or coal. Releases from these industries or from landfills can contaminate local air, and chromium in air can settle in nearby soil or water supplies. Contamination of water by naturally occurring chromium leaching from topsoil and rocks can also occur.
The most common health problems in workers exposed to chromium involves the respiratory system and include airway irritation, rhinitis, asthma, bronchitis, ulceration of the nasal mucosa, cough, shortness of breath, and wheezing. Workers have also developed allergies and sensitization to chromium compounds, which can cause breathing difficulties and skin rashes. Irritant and allergic contact dermatitis, and renal and liver toxicity can also occur. Gastrointestinal irritation, sperm damage, anemia have been seen in laboratory animals. Typically, health effects occur to a much greater degree with Cr(VI) than Cr(III). In workers, inhalation of Cr(VI) is an established human carcinogen, and has been linked to lung, nasal, and sinus cancer.
The issue of whether Cr(VI) causes cancer following ingestion in drinking water has been highly controversial. Some authors have argued that most ingested Cr(VI) is converted to the less toxic and less readily absorbed Cr(III) in the gastrointestinal tract and therefore is not absorbed at sufficient doses to cause cancer. However, studies in both animals and humans have shown that ingested Cr(VI) results in increased blood and tissue chromium levels and increased urinary half-life compared to Cr(III). In addition, studies done in laboratory animals by the National Toxicology Program have shown clear increases in intestinal adenomas or carcinomas in mice following ingestion of Cr(VI). In Liaoning Province, China, waste residues from a ferrochromium production facility contaminated local water supplies with Cr(VI) concentrations up to 5000 μg/L beginning in the mid-1960's. Investigations in the exposed areas for the years 1970–1978 showed evidence of increased mortality for both stomach and lung cancer. In another study, in the Oinofita municipality of Greece, associations were reported between Cr(VI) exposures in water (concentrations up to 44–156 μg/L) and increases in mortality from liver cancer. Results from other epidemiologic studies have mostly been negative. However, studies of Cr(VI) in water and cancer in humans are difficult to design since Cr(VI) causes water discoloration and becomes unpleasant to drink above a certain concentration. As a result, sufficiently large populations exposed to Cr(VI) concentrations that are high enough to cause increases in cancer that are large enough to be detected in an epidemiologic study with sufficient statistical power are difficult to identify. In addition, for most chemical contaminants that cause cancer, the latency period between the time when exposure begins and the time that the resulting cancer is large enough to be diagnosed clinically is usually several decades or more. In most instances, exposure records from this many years in the past are not available.
Most absorbed Cr(VI) is converted to Cr(III) and excreted in the urine within one day of ingestion. Chromium can be measured in the blood or urine but both represent only more recent exposure. Without obvious exposure sources, blood levels are generally less than 3.0 μg/100 mL and urine levels are generally less than 10 μg/L. For chronic low-dose exposures that typically occur with drinking water ingestion, no antidote is available and treatment primarily involves removal from exposure.
Nitrate and nitrite are nitrogen-oxygen chemical units whose chemical structures are NO3− and NO2−, respectively. Nitrate is formed naturally when nitrogen combines with oxygen or ozone. Nitrate is the more stable compound and is an important plant nutrient. In most people, food is the primary source of nitrate. Nitrates and nitrite are commonly found in leafy and other vegetables (lettuce, spinach, cauliflower) and many other foods. Nitrate can be converted by microbial reduction or in the human body to nitrite. Nitrite is also used as a preservative in cured meats.
In some people, exposure in drinking water can be an important source of nitrate. Nitrates in drinking water can result from either natural or manmade sources. Nitrogen from sources including fertilizer, animal and human waste, nitrogen oxides from utilities and automobiles, and some crops can be transformed to nitrate by various processes. The greatest industrial use of nitrates is as a fertilizer. Contamination of drinking water with nitrate can occur from runoff of agricultural fertilizer, leakage of wastes from septic tanks, improper sewage disposal, erosion of natural deposits, runoff from animal feedlots, industrial waste, food processing waste, or other routes. Private domestic ground water wells, especially shallower ones, in rural agricultural areas seem to be especially vulnerable. In one European Union report, nitrate levels greater than the WHO recommended levels of 50 mg/L were reported in about 30% of all groundwater bodies for which measurements were available. In addition to being ingested in food and water, nitrate is also formed endogenously in the human body as part of normal metabolism.
Once ingested, nitrate is reduced to nitrite, which can bind to hemoglobin in red blood cells to form methemoglobin. Methemoglobin binds to oxygen more tightly than hemoglobin and is therefore less effective at releasing oxygen to tissues. In infants, elevated methemoglobin levels (usually exceeding 10%) can cause cyanosis and difficulty breathing, the so called “blue baby syndrome.” Other symptoms can include tachypnea, vomiting, and diarrhea. Examination of the patient's blood reveals a chocolate brown color. Infants who drink water containing high concentrations of nitrate can become seriously ill and, if untreated, may die. Infants are thought to be especially susceptible for a variety of reasons including their less developed and effective repair and detoxification mechanisms; differences in gut pH and flora which may allow a more effective conversion of nitrate to nitrite; a greater presence of fetal hemoglobin which may be more readily oxidized to methemoglobin; and a greater intake of water on a per body weight basis than adults. Common risk factors for blue baby syndrome include age less than 3 months, a bottle-fed infant, glucose-6-phosphate dehydrogenase (G6PD) deficiency, gastrointestinal infections (which may increase conversion of nitrate to nitrite), private well use, and nitrate water levels greater than 50 mg/L.
Most regulatory standards for nitrate in drinking water are aimed at preventing blue baby syndrome, although increasing attention is being given to other possible adverse health effects, including cancer and thyroid deficiency. Nitrosating agents that arise from nitrite under acidic conditions, such as those found in the stomach, can react with secondary amines and amides and other nitrosatable compounds and form potentially carcinogenic N-nitroso compounds. The cancers most frequently studied include gastric, esophageal, brain, and urinary tract cancer, but to date, a clear causal association between nitrate in drinking water and cancer has not been established in humans. In its latest review on the topic (2010), the International Agency for Research on Cancer concluded that there was inadequate evidence in humans or animals for the carcinogenicity of nitrate in food or drinking water, limited evidence in humans for the carcinogenicity of nitrite in food (primarily for stomach cancer), and sufficient evidence in experimental animals for the carcinogenicity of nitrite in combination with amines or amides.
In laboratory studies, nitrate has been shown to block the uptake of iodide into the thyroid gland. Since iodide is a key component of thyroid hormone this can potentially lead to decreased thyroid hormone production and hypothyroidism. This mechanism has raised concern about the potential effects of drinking water nitrate on thyroid function. Several studies, primarily from agricultural areas in eastern Europe, have reported associations between exposures to nitrate in water and various thyroid effects included thyroid enlargement and goiter, and changes in thyroid hormone levels. However, in many of these studies it is not clear that researchers were blinded to the nitrate exposure status of the subjects when assessing their thyroid size. In addition, iodine intake levels may not have been adequately controlled for in some studies. Either inadequate or excessive iodine intake can also cause hypothyroidism. In some studies well water nitrate concentrations were well above recommended standards (ie, >50 mg/L of nitrate or 10 mg/L measured as nitrogen). In an experimental study, subjects receiving 15 mg of sodium nitrate per kilogram of body weight (over three times the WHO and European Commissions acceptable daily intake [ADI]) for a 28-day period showed no changes in thyroid hormones or decreases in thyroid iodide uptake. Overall, human research on the thyroid-inhibiting effect of nitrate at levels normally encountered in water is mixed and inconclusive.
About 60–70% of ingested nitrate is excreted in the urine within 24 hours and nitrate levels can be measured in either blood or urine. When evaluating nitrate levels in blood or urine it is important to consider that nitrate can come from multiple sources including food, water, and endogenous production. Treatment for blood baby syndrome due to nitrates can include methylene blue and supportive care. Methods of prevention include appropriate management of agricultural and farm animal practices to prevent runoff into nearby water supplies; careful placement, management, and maintenance of sewage facilities; and testing of ground water supplies, especially in rural agricultural areas.
Fluoride (F−) is monovalent anion derived from the element fluorine. Fluoride can combine with positive ions such as calcium or sodium to form stable compounds like calcium fluoride or sodium fluoride. These compounds can be released into the environment naturally in both water and air. Fluoride compounds also are produced by some industrial processes that use the mineral apatite, a mixture of calcium phosphate compounds. In humans, fluoride is found in calcified tissues like bones and teeth because it has a high affinity for calcium.
Fluoride often occurs naturally in drinking water sources and in some foods and beverages including those made with water from fluoridated municipalities. Analyses by the U.S. Food and Drug Administration have identified elevated levels of fluoride in some teas, seafood, raisins, wine, grape juice, and other foods. Fluoride is also used in a number of dental products such as toothpaste and is frequently added to drinking water to help prevent dental caries and most available evidence suggests it is effective at doing so.
Despite its effectiveness at reducing dental caries, there has been considerable worry among some that fluoride added to water in fluoridation programs may cause cancer or other serious health effects. Among the earliest research raising this concern was an ecologic analysis of cancer death rates for the period 1940–1969 comparing twenty large US cities with and without water fluoridation. Before fluoridation began (1952–1956), cancer mortality rates were increasing at similar rates in both sets of cities. This rise was expected as populations were aging and cancer reporting was improving. However, immediately after fluoridation began, cancer rates appeared to plateau in the unfluoridated cities but continued to rise in the fluoridated cities. After about 1960, rates again rose similarly in both sets of cities. The authors of this analysis concluded that the differences observed were related to fluoridation. However, major mortality risk factors like smoking, socioeconomic variables, race, and age were either not considered or only rudimentarily analyzed. In addition, the finding that cancer rates differed almost immediately after fluoridation began is unusual since most known chemical carcinogens take many years to increase cancer rates. Importantly, multiple subsequent analyses in the United States and in other countries have failed to confirm these findings. A 1990 study by the U.S. National Toxicology Program reported a small increase in osteosarcomas and thyroid adenomas and carcinomas in male rats, although no increases were seen in female rats or in mice and several follow-up animal studies have shown no cancer increases. More recently, a case-control study involving 103 cases of childhood osteosarcoma reported odds ratios as high as 4 in males, but not females, with elevated fluoride exposures but many of the details of the design and statistical analysis of this study were not provided. In addition, a larger follow-up study has reportedly found no association. Overall, most major authoritative bodies including the U.S. National Research Council have concluded that there is currently insufficient evidence to conclude that fluoride added to water to prevent tooth decay causes cancer.
Excessive fluoride consumption may increase bone fractures and cause bone pain and tenderness, a condition called skeletal fluorosis. However, severe skeletal fluorosis is relatively rare and usually only of concern for those living in areas with very high natural background levels of fluoride in water or in those with very high intakes of fluoride in their diets. There has also been some concern regarding dental fluorosis, a discoloring (white spots or brown stains) and pitting of the enamel of the teeth due to fluoride. Dental fluorosis primarily affects children age 8 and younger when teeth are growing. Apatite crystals in developing teeth can bind and integrate fluoride ion into the crystal lattice of the tooth and failure of the enamel covering of the teeth to crystallize can lead to the signs of fluorosis. Recent data suggest that some cases of dental fluorosis may occur even at fairly common intake levels of fluoride (eg, 0.05 mg/kg), although the large majority of these cases are mild and only a minor cosmetic concern. Recently, in an attempt to maximize the benefit of water fluoridation in preventing dental fluorosis while limiting the risks of dental fluorosis, the U.S. Department of Health and Human Services (HHS) has proposed lowering its recommended upper limit of fluoride in water from 1.2 to 0.7 mg/L.
Gaseous or liquid forms of chlorine are commonly added to drinking water as a disinfection agent. In water, these agents react to form hypochlorous acid or hypobromous acid (in the presence of bromine) and these are very effective at killing harmful bacteria, protozoa, and viruses. The use of chlorine in this way has revolutionized water purification and reduced the incidence of waterborne infections and disease across the world, and chlorination and/or filtration of drinking water has been called one of the major public health achievements of the twentieth century. Other disinfection agents added to drinking water include chloramines, chlorine dioxide, and ozone. In the presence of organic material such as decaying plants or algae, a variety of potentially toxic agents can be formed when adding chlorine to water. The most common of these are trihalomethanes (THM) and haloacetic acids (HAAs), although many other compounds in smaller amounts can also be formed. Collectively these are known as disinfection by-products (DBPs) and hundreds of different ones may occur in chlorinated tap water, although most at very low levels. Common forms of trihalomethanes include chloroform (CHCl3), bromodichloromethane (BDCM) (CHCl2Br), dibromochloromethane (DBCM) (CHClBr2), and bromoform (CHBr3). Common forms of HAAs in drinking water, and those five compounds regulated by the U.S. Environmental Protection Agency (U.S. EPA), include monochloroacetic acid (MCA) (CH2ClCOOH), dichloroacetic acid (DCA) (CHCl2COOH), trichloroacetic acid (TCA) (CCl3COOH), monobromoacetic acid (MBA) (CH2BrCOOH), and dibromoacetic acid (DBA) (CHBr2COOH). In the United States, an estimated 200 million or more people are served by water systems that apply a water disinfectant such as chlorine. In addition to ingestion, significant exposure to DBPs from water may also occur from showering or bathing as a result from inhalation or dermal absorption.
DBPs have been linked to a variety of health effects including anemia; liver, kidney, and central nervous system toxicity; reproductive and developmental effects; and cancer, although findings for some of these outcomes are not consistent across all studies and many may only be observable at exposure levels much higher than those commonly found in most drinking water sources. Based primarily on evidence from animal studies showing increases in kidney, liver, or other tumors, the International Agency for Research on Cancer has classified chloroform, bromodichloromethane, dibromoacetic acid, and dichloroacetic acid as possibly carcinogenic to humans (Group 2B). More recently, a 2011 pooled analysis of three large case-control studies in Europe reported a statistically significant association between total THM levels greater than 50 μg/L in residential water and bladder cancer but only in men, not in women. A number of other human epidemiologic studies have reported associations between various DBPs in water and cancers of the bladder and gastrointestinal tract but findings are not consistent across all studies and issues such as difficulties in assessing historical exposures, difficulties in isolating the effects of a single or a few combined agents when multiple chemical agents are present, and potential confounding factors make it difficult to interpret some findings. The U.S. EPA does not regulate individual THMs or HAAs but rather regulates these agents as total THMs and total HAAs.
Radioactive mineral extraction used during cold war military activities and for the purposes of fueling nuclear power plants has led to surface and groundwater contamination with radionuclides. These radioactive materials include radium, uranium, and their decay products. In a number of areas, water has been significantly contaminated with tritium and alpha emitters as a result of these activities. In some localities, some believe that these elevated concentrations of waterborne radionuclides may be responsible for elevated childhood leukemia rates.
Erosion of natural deposits also leads to contamination of groundwater and drinking water sources. Drinking water contaminated by naturally radioactive derivatives of the uranium and thorium decay series accounts only for a very small portion of the total annual dose of radiation for most humans. In some situations, the risk of leukemia and other cancers may be elevated for those who live above or drink from groundwater sources that contain higher than normal radionuclide decay products including radon. Extensive study of the quantitative cancer risk associated with radon in groundwater and drinking water has been undertaken. In some studies, the risk is considered to be formidable. Currently, the U.S. EPA has regulatory drinking water standards for alpha particles (15 pCi/L), beta particles, and photon emitters (4 millirems per year), radium 226 and 228 (5 pCi/L combined), and uranium (30 μg/L), all based on possible increased cancer risks.
Globally, agriculture accounts for 70% of all water consumption, compared to 20% for industry and 10% for domestic use. In industrialized nations, however, other uses such as cooling of thermoelectric power plants are larger consumers. Agriculture is the industry with the most direct access to surface and groundwater resources. The use of pesticides to control weeds, insects, and other pests has resulted in increased food production and reduced insect-borne disease, but because agriculture is universally chemically intensive and the chemicals generally are applied in solution, suspension, or as wettable concentrates and powders, agricultural chemicals can produce serious water pollution problems. In the past 50 years, the development of chemically intensive agriculture in every country has led to the contamination of water supplies with many evanescent and persistent chemicals.
In the 1960s, water pollution from organomercurial seed-coating fungicides used on the Indian subcontinent led to the contamination of deep-sea tuna with levels of mercury that were unacceptable to Western countries. The source of this organic mercury was the fungicidal substances that were applied to rice seed. Because the use of organomercurials produced a dramatic increase in rice yield per acre, it was inevitable that those countries in the Indian subcontinent that depend on rice to prevent starvation would continue to use the mercurials. Only recently have runoffs from the rivers of Asia had reduced levels of mercury. Organic mercury contamination from seed-coating fungicides, paper-pulp fungicides, and cooling-tower biocides has been a major cause of water pollution in Japan, the Indian Ocean, and Scandinavia. Fungicides containing mercury are now banned in the United States and some other countries.
Perhaps of even greater significance currently is the widespread contamination of drinking and groundwater supplies of wells and rivers throughout Europe, Asia, and North America with herbicide chemicals. In a national scale analysis by the U.S. Geological Survey (USGS) from 1992 to 2001, at least one pesticide was found in every stream tested and in the majority of all ground water sources tested, including one-third of all deep wells. In a more recent USGS report, common pesticides detected streams in agricultural areas included chlorpyrifos, azinphosmethyl, atrazine, p,p′-DDE, and alachlor. In urban streams, common pesticides were simazine, prometon, metolachlor, diazinon, carbaryl, and fipronil. Pesticides usage and water contamination vary by region and regional maps of the estimated use of hundreds of different pesticides in the United States are available from the USGS at http://water.usgs.gov/nawqa/pnsp/usage/maps/compound_listing.php.
Atrazine, a triazine herbicide used for weed control, appears in virtually every well in every area of the United States where it has been used. In many parts of the world, dibromochloropropane (DBCP) contamination of groundwater has occurred as a result of the direct injection of this carcinogenic compound into the soil for the control of nematodes in bananas, pineapples, and sugar beets. Dibromochloropropane causes male sterility in agricultural and manufacturing workers who make or apply it. The widespread contamination of groundwater with this reproductive toxin has been reported in Costa Rica, Honduras, the Philippines, Ivory Coast, and California.
Some research in humans has linked pesticide exposure to a variety of health effects including cancer and adverse impacts on childhood neurodevelopment, but much of this research has been done in pesticide applicators or other farm workers and their families where overall exposures are likely to be higher than those typically found in drinking water. To date clear associations between health effects and commonly reported lower levels of pesticides in water have not been established although few large, comprehensive studies have been done. Given this unknown, and the documented toxicity of many of these agents at higher exposures, it remains prudent to limit the contamination of water supplies by these agents as much as possible. Peroxide and ultraviolet treatment of waste water significantly degrades pesticide residues. In the home, point-of-use devices like charcoal and reverse-osmosis filters can also be used to remove or minimize some pesticides in drinking water.
Other Toxic Agents in Water
A variety of other agents can be found in water sources. Copper in drinking water can result from leaching from copper pipes. Copper is a required nutrient and deficiencies can lead to hematologic abnormalities (anemia, neutropenia, and leukopenia), osteoporosis, and myeloneuropathy. However, at higher exposures, copper in water has most commonly been linked with symptoms of gastrointestinal distress including nausea, vomiting, and abdominal pain, especially in young children. Cadmium-induced nephropathies, and itai-itai (“ouch-ouch”), a cadmium-induced systemic disease, occurred in Japan as a result of the contamination of estuarine waters that provided most of the dietary fish to a large population. In Croatia, Serbia, and Bosnia, and some rural villages in Romania, Balkan endemic nephropathy is a chronic kidney disease associated with carcinomas of the upper urinary tract. In the past it was thought to be the result of certain water contaminants. However, recent studies indicate that it is a chronic dietary poisoning by aristolochic acid, a chemical commonly found in Chinese herbal teas.
Specific industries have been associated with local water contamination. For example, some mining operations have been associated with acid mine drainage. In addition, high concentrations of lead, zinc, nickel, vanadium, manganese, mercury, and iron have been demonstrated in surface and ground water adjacent to and downstream from mines, mineral extraction facilities, or mine tailing piles. In the pulp and paper industry, discharge of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and its congeners from chlorine-based pulp bleaching plants has contaminated nearby streams and rivers in the United States. These highly persistent organics are transferred to silt, sediment, and biota. From the silt, toxics are transferred to fish in the stream ecosystem. These pollutants may then be concentrated manyfold within the fish before humans or animals consume the chemicals. When sportsmen or subsistence fishermen consume contaminated fish, they may further concentrate these toxins.
Leakage of gasoline products from underground storage facilities continuously inputs significant quantities of toxic and carcinogenic hydrocarbons such as benzene, toluene, xylene, and MTBE (methyl tert-butyl ether) into ground water supplies that may be used for drinking. These volatile hydrocarbons are also released into the air of the homes of persons who live above contaminated ground-water plumes. Contaminant plumes could potentially be the cause of human illnesses such as immunologic impairment, neurologic and cognitive deficits, birth defects, and cancers characteristic of exposure to these substances at high levels.
High-technology industries such as semiconductor manufacturing plants use large quantities of halogenated organics such as trichloroethylene (TCE), trichloroethane, perchloroethylene, and carbon tetrachloride. Other chemicals used include complex organics and metals and metalloids such as arsenic, selenium, beryllium, cadmium, and lead. These materials may enter the waste water discharge systems of the facilities or local ground water supplies either by design or in error (eg, leaking from underground storage facilities). Groundwater contamination problems, in particular contamination with 1,1,1-trichloroethane, TCE, and other volatile organic compounds, has occurred in the Silicon Valley of California. Based primarily on studies in highly exposed workers, several recent meta-analyses have linked TCE to cancers of the kidney and other organs.
A large amount of water is used in the United States and elsewhere for cooling coal- and other fossil-fuel-fired plants. These facilities treat this water with certain chemicals to help prevent corrosion of the cooling towers and to arrest growth of bacteria in the cooling water. For many years, the principal materials used to prevent cooling-tower corrosion were Cr(VI) compounds. Organic mercurials were used as cooling-tower biocides. These materials are no longer used for these purposes in the United States, but continue to be used elsewhere in the world. These highly toxic materials may be disposed of directly to the water systems. At best, they are impounded and evaporated. From impoundment ponds they may reach the groundwater after subsequent leaching caused by rain and runoff. In California, the groundwater supply of at least one community has been severely contaminated by the practice of disposing of cooling-tower wastes containing Cr(VI) from a natural gas compression plant into nearby unlined waste water ponds.
Mercury is a naturally occurring element but industrial processes such as coal-fired power generation, waste incineration, and smelting can also release mercury into the air, and this mercury can eventually settle into lakes, rivers, and the ocean. Once in the water, bacteria in the sand or mud can convert it into methylmercury. Fish absorb this methylmercury when they eat smaller organisms. Because it is excreted only very slowly, methylmercury can build up over time, and bioaccumulate as larger and older fish eat smaller fish and other organisms. A consequence is that methylmercury levels are usually highest in those fish at the top of the food chain. Removal of mercury from contaminated waterways can take many years. For example, studies of trout and perch in Scandinavia show that decreases in mercury tissue concentration since the 1970 ban on the use of phenyl mercury in pulp and paper production have been very slow. Even though a river habitat is involved in their studies, 15 years is required for mercury levels in trout in the mercury-polluted waters downstream from a pulp and paper plant to fall to a level equal to that in the trout upstream of the plant. Methylmercury seems to be especially toxic to the developing neurologic system and studies in heavy seafood-eating populations in the Seychelles Islands, the Faeroe Islands, and elsewhere have identified associations between mercury consumption in mothers and adverse cognitive development in the offspring including decreases in learning ability, language skills, attention, and memory. Based on these studies, many state and local agencies provide information about mercury levels in local fish and produce advisories regarding the maximum number of meals of fish that should be consumed per week, especially in pregnant women, and these local advisories can frequently be found online from the U.S. EPA or various state agencies.
Bisphenol A (BPA) is a man-made carbon-based synthetic compound used to make polycarbonate plastics used in food packaging and water bottles. In a large 2003–2004 nationwide survey in the United States, BPA was detected in the urine of 93% of all subjects tested. BPA has raised concerns because it appears to mimic the effects of estrogen, and some animal studies, but not all, have identified links between BPA exposure and a variety of effects related to neural and behavior alterations, potentially precancerous lesions in the prostate and mammary glands, altered prostate gland and urinary tract development, and early onset of puberty in females. BPA continues to be used, but because of these concerns, some countries have banned the use of BPA for specific products such as baby formula bottles.
Very large deposits of shale containing oil and natural gas are buried deep underground in several parts of the United States and in other countries. Historically, these deposits were difficult and very costly to access. However, recent advances in horizontal drilling and hydraulic fracturing (or “fracking”) have made it more feasible to extract natural gas and oil from these sources. The process involves initially drilling down, commonly over one to two miles deep. Once the deposit is reached, the well is then drilled horizontally for several thousand feet. Cement and steel casings are inserted to prevent leaks. Fluid containing water, sand, and various chemicals is then pumped down the well under extremely high pressure, and this high-pressure fluid fractures the surrounding rock. This fracturing releases gas and oil which are then pumped back up the well along with the fluid used to fracture the rock (“flowback”). The volume of fracturing fluid pumped into each well is between 2 and 7 million gallons. Some of this fluid is recycled and some is pumped into disposal wells or other waste sites. This process has helped lead to a tremendous increase in natural gas production in the United States. In 2010, shale gas contributed 23% of domestic natural gas production, compared with only 2% in 2000.
Unfortunately, this process has also led to several environmental concerns, including the tremendously high water usage, the production of large amounts of waste water containing a variety of potentially toxic materials, and the possible contamination of local groundwater used for drinking by the residents living near the wells. A large number of chemicals are added to fracking fluid in order to help initiate cracks in the rock, keep fractures open, prevent pipe corrosion, decrease pumping friction, and as gelling agents, bactericides, biocides, clay stabilizers, scale inhibitors, and surfactants. Chemicals found in fracking fluid or waste water include hydrochloric acid, ethylene glycol, xylene, methanol, metals, as well as several known carcinogens like formaldehyde and benzene. Over 600 different chemicals have been identified as being used in fracking fluid. For the most part, however, the chemicals used in any particular well are considered by some companies to be proprietary information and are not disclosed. There have been concerns about contamination of the local groundwater from the salts, chemicals, and naturally occurring radioactive material present in flowback, which is usually temporarily pumped into wastewater ponds and then moved off-site, where it is reinjected back into the ground or transferred to wastewater treatment facilities for treatment and disposal. The majority of flowback that is not disposed of in injection wells is treated at centralized waste treatment (CWT) facilities that are designed to treat industrial wastewater, and which may then discharge into sewers or surface water bodies.
Currently there are no federal regulations requiring natural gas companies to disclose information about the chemicals used in hydraulic fracturing fluids. Hydraulic fracturing and reporting of the chemicals used in fracturing fluids exempt from the U.S. Emergency Planning and Community Right-to-Know Act (EPCRA). Section 313 of EPCRA created the Toxic Release Inventory (TRI), which requires companies that manufacture and/or use toxic chemicals to report information on chemicals, including identities and quantities that are stored, released, transferred, or “otherwise used.” In 2005, Congress passed the Energy Policy Act exempting fracking from regulation under the 1974 Safe Drinking Water Act. Some states are attempting to regulate the fracking industry but to date the effectiveness of these efforts are unclear.