Toxins in Everyday Life - Chemical Toxins
lead releases site chemicals
Hundreds of chemicals released into the air, water, and the food chain are harmful to the environment—to humans as well as other living things. Under the Federal Insecticide, Fungicide, and Rodenticide Act (61 Stat 163; amended 1988, PL 100-532), the Environmental Protection Agency (EPA) is charged with reviewing chemical studies and taking appropriate action, including banning dangerous substances. The EPA may regulate the manufacture, importation, processing, distribution, use, and disposal of any chemical that poses a risk to human health or the environment. Regulatory tools used by the EPA range from requiring a substance to bear a warning label, to placing a total ban on production and importation. The EPA reviews more than 2,000 new chemicals each year, and research and testing continually find new substances to add to this list.
Among the most common contaminants identified as harmful are DDT, kelthane, lindane, some synthetic pyrethroids, dioxins, polychlorinated biphenyls (PCBs), furans, some heavy metals such as lead and cadmium, and some plastics. Solvents are common in industrial applications but are also found in such products as furniture polish, bathroom tile cleaners, disinfectants, and shoe polish.
Of the thousands of chemicals currently produced in the United States, many have yet to be tested to see whether they might cause cancer, birth defects, infertility, or abnormal growth in children. Some observers charge that the EPA follow-up on warnings of adverse effects has been slow and, sometimes, has enabled dangerous pesticides to remain on the market.
Toxic Release Inventory
In 1984 a deadly cloud of chemicals was released from the Union Carbide pesticide plant in Bhopal, India, following an explosion in the plant. The methyl isocyanate gas killed approximately 3,000 people and injured 200,000 others. Shortly after, a similar chemical release occurred in West Virginia, where a cloud of gas sent 135 people to the hospital with eye, throat, and lung irritation complaints. There were no fatalities. Such incidents fueled the demand by workers and the general public for information about hazardous materials in their areas. As a result Congress passed the Emergency Planning and Community Right-to-Know Act of 1986 (EPCRA; PL 99-499).
The EPCRA established, among other things, the Toxics Release Inventory (TRI), a publicly available database (http://www.epa.gov/tri) that contains information on toxic chemical releases by various facilities. More than 650 toxic chemicals are on the TRI list.
Certain manufacturing facilities (which are called "original" industries under the program) have had to file TRI reports since 1987. In 1998 the program was expanded to include certain facilities within a group of industries called the "new" industries. These "new" industries include metal and coal mining, electric utilities burning coal or oil, chemical wholesale distributors, petroleum terminals, bulk storage facilities, Resource Conservation and Recovery Act subtitle C hazardous water treatment and disposal facilities, solvent recovery services, and federal facilities. The requirements only apply to facilities that use certain thresholds of toxic chemicals and that employ ten or more full-time workers.
The 2001 Toxics Release Inventory (TRI) Public Data Release Report was published in July 2003. Facilities reported a total of 6.16 billion pounds of chemical releases in 2001. On-site releases to air, land, and water accounted for 91 percent of all releases, while off-site releases (when a facility sends toxic chemicals to another facility where they are then released) accounted for the remainder. Most (56.2 percent) releases were to landfills or surface impoundments. Air emissions accounted for just over 27 percent of the total. Releases via underground injection to deep wells and releases to surface water accounted for nearly 4 percent each. (See Figure 5.18 in Chapter 5.)
In 2001 the metal mining industry accounted for the largest amount of total emissions (45 percent), followed by electric utilities (17 percent), and the chemical industry (9 percent). (See Table 8.1.) The 20 chemicals with the largest releases in 2001 are listed in Table 8.2. These 20 chemicals accounted for the vast majority (88 percent) of the total releases. The metal compounds were primarily released via landfills or some other type of land release.
The organic chemicals, acids, and chlorine were mainly released in air emissions, while nitrate compounds were primarily discharged to surface waters.
The TRI report for 2001 focused on a group of chemicals called persistent bioaccumulative toxic (PBT) chemicals. These are toxic chemicals that persist in the environment a relatively long time and accumulate in the tissues of plants, animals, and humans. The TRI describes releases of 454 million pounds of PBT chemicals in 2001, including dioxins, lead, mercury, polycyclic aromatic compounds, PCBs, pesticides, and other complex organic compounds. (See Table 8.3.)
Pesticides and Herbicides
Pesticides are chemicals used to kill or control insects. Herbicides are chemicals used to kill or control vegetation, particularly weeds. These are a unique group of chemicals because they are specifically formulated to be toxic (to some living things) and are deliberately introduced into the environment. Due to these two facts they are closely regulated. The EPA reviews every pesticide for every particular use.
According to the August 2002 EPA report Pesticides Industry Sales and Usage: 1998 and 1999 Market Estimates by David Donalson et al., approximately 70 percent of all pesticides sold in the United States are used for agricultural purposes. Agricultural pesticide use costs $11 billion annually. Every dollar spent on agricultural pesticides is estimated to return about $4 in crops saved. Agricultural dependence on chemicals developed since the 1940s. Prior to that time natural methods, such as crop rotation, mechanical weed control, and other practices, were used to control pests and weeds.
Agricultural use of pesticides grew steadily through the 1960s and 1970s and leveled off at about one million pounds of active ingredient per year. This level has remained relatively constant since the 1980s. Pesticide use in the 1960s centered around organochlorines, including DDT, aldrin, and toxaphene. The environmental dangers and health hazards of these chemicals gradually led to their replacement with other types of pesticides, mainly pyrethroids.
Pesticides have been detected in surface waters, groundwater, and even rainfall. In 2001 the U.S. Geological Survey (USGS) announced that testing performed for the National Water Quality Assessment Program had found at least one pesticide in more than 95 percent of stream samples and in more than 60 percent of shallow agricultural wells. Although the concentrations were generally low and below drinking water standards, their effects on the environment and human health are not known for certain.
The study also found sediments contaminated with persistent organochlorine pesticides, such as DDT, dieldrin,
|Underground injection||On-site land releases||Off-site releases|
|SIC code industry||industry||Total facilities Number||Total forms Number||Total air emissions Pounds||Surface water discharges Pounds||Class I wells Pounds||Class II-V wells Pounds||RCRA Subtitle C landfills Pounds||Other on-site land releases Pounds||Total on-site releases Pounds||Transfers off-site to disposal Pounds||Total on- and off-site releases Pounds|
|-||Multiple codes 20-39||1,317||4,869||66,687,839||16,511,697||1,723||10||263,125||5,360,924||88,825,318||15,100,990||103,926,308|
|-||No codes 20-39||348||887||3,369,277||1,065,165||0||0||3,884||8,204,785||12,643,111||1,120,451||13,763,561|
|5169||Chemical wholesale distributors||475||3,335||1,254,310||1,856||5||0||5||1,074||1,257,250||211,020||1,468,270|
|5171||Petroleum bulk terminals/bulk storage||596||4,779||21,164,969||11,177||0||100||26||11,215||21,187,488||153,163||21,340,651|
|7389/4953||Hazardous waste/solvent recovery||223||2,762||974,414||23,498||22,678,278||0||129,266,508||15,482,910||168,425,606||51,446,405||219,872,011|
|Notes: Off-Site releases include metals and metal category compounds transferred off-site for solidification/stabilization and for wastewater treatment, including to publicly owned treatment works (POTWs). Off-site releases do not include transfers to disposal sent to other Toxics Release Inventory (TRI) facilities that reported the amount as an on-site release. RCRA Resources Conservation and Recovery Act.|
|SOURCE: "Table ES-3: TRI On-site and Off-site Releases by Industry, 2001," in 2001 Toxics Release Inventory Public Data Release, U.S. Environmental Protection Agency, Office of Waste, Washington, DC, 2003|
|Underground injection||On-site land releases||Off-site releases|
|CAS number||Chemical||Total air emissions Pounds||Surface water discharges Pounds||Class I wells Pounds||Class II-V wells Pounds||RCRA Subtitle C landfills Pounds||Other on-site land releases Pounds||Total on-site releases Pounds||Transfers off-site to disposal Pounds||Total on- and off-site releases Pounds|
|1330-20-7||Xylene (mixed isomers)||47,081,406||21,972||80,521||550||133,072||44,222||47,361,743||1,158,921||48,520,664|
|Subtotal (top 20 chemicals)||1,328,959,329||214,969,533||95,208,731||20,909,880||50,981,817||3,222,009,165||4,933,038,455||464,565,380||5,397,603,835|
|Total (all chemicals)||1,679,373,058||220,796,115||193,436,563||21,987,723||138,220,131||3,326,460,403||5,580,273,993||577,723,085||6,157,997,078|
|Notes: Off-site releases include metals and metal category compounds transferred off-site for solidification/stabilization and for wastewater treatment, including to publicly owned treatment works (POTWs). Off-site releases do not include transfers to disposal sent to other Toxics Release Inventory (TRI) facilities that reported the amount as an on-site release. RCRA Resources Conservation and Recovery Act.|
|SOURCE: "Table ES-4: Top 20 Chemicals with the Largest Total Releases, 2001," in 2001 Toxics Release Inventory Public Data Release, U.S. Environmental Protection Agency, Office of Waste, Washington, DC,|
|Underground injection||On-site land releases||Off-site releases|
|CAS number||Chemical||Total forms Number||Total air emissions Pounds||Surface water discharges Pounds||Class I wells Pounds||Class II-V wells Pounds||RCRA Subtitle C landfills Pounds||Other on-site land releases Pounds||Total on-site releases Pounds||Transfers off-site to disposal Pounds||Total on- and off-site releases Pounds|
|Dioxin and dioxin-like compounds*||1,320||6.37||4.08||0.14||0.19||21.97||94.39||127.14||200.88||328.01|
|-||Dioxin and dioxin-like compounds (in grams)*||1,320||2,887.566||1,850.869||63.881||84.270||9,963.843||42,807.558||57,657.988||91,100.805||148,758.793|
|Lead and lead compounds||8,561||1,633,121.66||413,419.80||206,138.00||6,026,683.34||18,610,199.14||360,809,675.39||387,699,237.33||55,292,470.94||442,991,708.27|
|Mercury and mercury compounds||1,665||150,462.84||1,805.15||1,741.11||8,035.04||60,008.84||4,455,980.78||4,678,033.75||228,282.95||4,906,316.70|
|Polycyclic aromatic compounds||3,813||1,177,581.28||17,069.76||2.10||332.95||97,094.05||71,292.51||1,363,372.65||1,622,784.90||2,986,157.55|
|191-24-2||Benzo(g, h, i)perylene||1,509||31,455.26||685.17||1.00||1.65||3,716.71||4,852.90||40,712.69||86,240.63||126,953.32|
|-||Polycyclic aromatic compounds||2,304||1,146,126.02||16,384.58||1.10||331.30||93,377.34||66,439.62||1,322,659.96||1,536,544.27||2,859,204.23|
|1336-36-3||Polychlorinated biphenyls (PCBs)||137||1,359.90||2.80||0.00||0.00||2,265,476.30||225,685.85||2,492,524.85||12,251.02||2,504,775.86|
|Notes: Off-site releases include metals and metal category compounds transferred off-site for solidification/stabilization and for wastewater treatment, including to publicly owned treatment works (POTWs). Off-site releases do not include transfers to disposal sent to other toxics release inventory (TRI) facilities that reported the amount as an on-site release.|
|*The chemical category dioxin and dioxin-like compounds is reported in grams. Where the category dioxin and dioxin-like compounds is shown on a table with other TRI chemicals, it is presented in pounds. The grams are converted to pounds by multiplying by 0.002205. RCRA Resource Coservation and Recovery Act.|
|SOURCE: "Table ES-5: TRI On-site and Off-site Releases, PBT Chemicals, 2001," in 2001 Toxics Release Inventory Public Data Release, U.S. Environmental Protection Agency, Office of Waste, Washington, DC, 2003|
and chlordane, at more than 20 percent of agricultural sites tested. Use of these pesticides has been restricted for several decades, but many of them are "persistent," which means they do not easily degrade. DDT, in particular, can latch tightly onto soil particles, where it can persist for decades. DDT is also bioaccumulative, which means it can work its way from a nonliving medium, such as dirt, to a plant or animal. Since it is not easily broken down by metabolization within living creatures, DDT moves up the food chain as plants and animals containing DDT are consumed by others.
While pesticides have important uses, studies show that some cause serious health problems at certain levels of exposure. For example, pesticide by-products have been linked to breast cancer in humans. Researchers have found that breast tissue from some women with malignant breast tumors contained more than twice as many PCBs and DDE (a component of the pesticide DDT) than are found in the tissue of women who do not have cancer. Scientists indicate that the carcinogen is stored in body fat, making obesity a risk factor for breast cancer.
In general the level of persistent toxins, including pesticides, has declined in humans and wildlife since the 1970s. Newer pesticide compounds are often more toxic than the older types of pesticides but they are generally designed to be less persistent in the environment and tend to cause fewer chronic problems such as birth defects. However, even pesticides originally believed safe are sometimes found to be harmful. In June 2000 researchers announced that recent tests of the pesticide dursban, a very commonly used chemical in residences, found the substance to be harmful, and many applications were withdrawn from the market. Ironically, dursban was often used as a substitute for chlordane, a chemical also withdrawn from use after being discovered to be harmful.
Fear of agricultural toxins has contributed to a rise in the interest in "organic" foods. The federal government's National Organic Program defines organic agriculture as that which excludes the use of synthetic fertilizers and pesticides. More importantly it strives for low environmental impact and enlists natural biological systems—cover crops, crop rotation, and natural predators—to increase fertility and decrease the likelihood of pest infestation.
Beginning in 1962 approximately 19 million gallons of herbicides were sprayed over South Vietnam, primarily by aircraft, to defoliate vegetation used as cover for enemy troops in the Vietnam War. In 1969 studies linked chemicals in one of these herbicides, Agent Orange (named after the orange band used to mark the drums it was stored in), to birth defects in laboratory animals. Use of the defoliant was subsequently stopped in 1971. However, Vietnam has estimated that more than one million of its citizens were exposed to the spraying, and tens of thousands of Americans who served in the war are also believed to have been exposed to the chemical, which is a form of dioxin. (In 1994 the EPA affirmed the health danger posed by dioxin.)
Title 38 of the United States Code prohibits veterans from suing the government for injuries suffered while in the military. However, many Vietnam veterans have sued the manufacturers of Agent Orange for damages because of health problems experienced since their return from Vietnam. In 1979 a number of claimants filed a class action suit, In re Agent Orange Product Liability Litigation, which was settled out of court in 1987 for $180 million. The final funds in the case were distributed in 1992. Additional suits against the manufacturers have been attempted but have been prohibited by the courts. The most strongly fought of these legal battles, Ivy v. Diamond Shamrock, was supported by the attorneys general of all 50 states. The Supreme Court, however, refused to hear the arguments and the case ended in 1992. The court decreed that the issue was res judicata (the matter is settled).
The Department of Veterans Affairs sponsored a study of Agent Orange and announced its findings in 1996. The veterans' illnesses were grouped into four categories: (1) those that have a positive association with the herbicide; (2) those for which there is suggestive, but not conclusive, evidence of a link; (3) those for which there is insufficient evidence to make a determination; and (4) those for which there is little or no evidence of an association. The report also emphasized the need for further study. The illnesses that the study positively linked to herbicide use were soft-tissue sarcomas (a form of cancer), non-Hodgkin's lymphoma, Hodgkin's disease, and the skin disease chloracne. The second category included respiratory cancers, prostate cancer, multiple myeloma, acute peripheral neuropathy (nerve numbness or weakness), and spina bifida (a congenital deformity of the spine) in children of veterans. The federal government has generally agreed to pay medical claims on those illnesses.
Endocrine Disrupters—Environmental Hormones
Medical and scientific researchers are increasingly linking chemical compounds known as organochlorines to the endocrine systems of humans and wildlife. The endocrine system—also called the hormone system—is made up of glands located throughout the body, hormones that are synthesized and secreted by the glands into the bloodstream, and receptors in the various target organs and tissues. The receptors recognize and respond to the hormones. The function of the system is to regulate the many bodily processes, including control of blood sugar, growth and function of the reproductive systems, regulation of metabolism, brain and nervous system development, and development of the organism from conception through adulthood and old age.
Substances that interfere with these processes are called "endocrine disrupters." Although some occur naturally—for example, plant-derived hormones—most appear to be man-made. Disruption of the endocrine system can produce certain genetic, reproductive, and behavioral abnormalities in humans and wildlife; increases in several types of cancer not related to smoking or age; malformations; and nervous system disorders.
Endocrine disrupters are sometimes referred to as "environmental estrogens" because they are so widely dispersed in the environment that they turn up in rain water, well water, lakes, and oceans, as well as in foods consumed by birds, fish, animals, and humans. Some scientists worry that organochlorines mimic or block the action of natural estrogen, thereby disrupting the endocrine system.
Some effects of certain estrogenic compounds have been well known for some time. Among these are the eggshell thinning and cracking that led to the population decline of the American bald eagle; the reproductive abnormalities of women exposed in utero to diethylstilbestrol, a synthetic estrogen prescribed between 1948 and 1971 to prevent miscarriages; and reported declines in the quantity and quality of sperm in humans. In 1996 researchers at the National Biological Service, in a study of Columbia River otters, found a direct correlation between the level of chemicals and pesticides in the otters' livers and the size of the males' genitalia.
Only recently, however, have researchers begun to realize how many compounds in the environment are estrogenic. More than 50 of these endocrine-disrupting chemicals have been observed to disrupt the hormone or reproductive system, but the remainder of the 85,000 chemicals currently in use remain to be studied. Among them are many herbicides, pesticides, insecticides, and industrial cleaning compounds. Many such compounds have been banned in the United States. Nonetheless, they persist in the food chain for many years and accumulate in animal tissue. Moreover, many of these chemicals continue to be used in developing countries.
Researchers in North America and Europe are studying the possibility of a link between environmental estrogens and the occurrence of birth abnormalities, Alzheimer's disease, sterility in both males and females, hyperactivity in children, neurological illnesses, and many cancers. Both men and women appear to be susceptible to endocrine disruption. In men, some studies show that estrogenic compounds affect the development of the Sertoli cells in the testicles. These cells secrete masculinizing hormones that regulate sperm production, the descent of the testicles, and the development of the urethra.
Because of the potentially serious consequences of human exposure to endocrine-disrupting chemicals, Congress included specific language on endocrine disruption in the Food Quality Protection Act of 1996 (PL 104-170) and Safe Drinking Water Act Amendments of 1996 (PL 104-182). The first mandated the EPA to develop an endocrine-disrupter screening program (EDSP), while the latter authorized the EPA to screen endocrine disrupters found in drinking water. In May 2002 the EPA presented its latest report to Congress on the program's progress. The agency plans to implement the EDSP by setting screening priorities for various chemicals and by establishing uniform laboratory tests for determining which chemicals affect humans similarly to naturally occurring hormones.
Chlorine is a gaseous element first isolated in 1774 by chemist Wilhelm Scheele. The gas has an irritating odor and, in large concentrations, is dangerous. It was the first substance used as a poisonous gas in World War I. It can be liquefied under pressure and is usually transported as a liquid in steel bottles or tank cars.
The use of chlorine to disinfect water supplies is one of the greatest public health success stories of the twentieth century. First used to purify water in the early 1900s, chlorine is, by far, the world's primary water disinfectant and is indisputably valuable in preventing the spread of disease. It is inexpensive, effective, and available nearly everywhere. It is credited with banishing typhoid fever, cholera, and dysentery from the United States and elsewhere. About three-fourths of all U.S. drinking water is chlorinated to kill parasites, viruses, and bacteria, while most of the rest is treated with a combination of chlorine and ammonia.
Researchers, however, are trying to determine if there is any connection between chlorine in drinking water and bladder and rectal cancer in humans. When chlorine is added to water containing organic matter, it produces byproducts (such as chloroform) that are suspected of causing harm to humans and other species. Environmentalists contend that chlorine is responsible for a thinning ozone layer and for causing reproductive malformations in aquatic species and cancer in humans.
Many sources claim that reducing or eliminating chlorine in water would cost many lives. Although the body of evidence seems to show a slight increase in cancer risk from chlorine by-products, most scientists consider the risk not "statistically significant" and believe that the risks to public health would be far greater if chlorine were to be reduced or eliminated.
Although researchers are investigating alternatives to chlorination, none have been found as effective and economical. Ozonation is used by some municipal systems, because ozone is an even more powerful disinfectant than chlorine. Ozonation is widely used in Europe. However, ozone is costly to generate, and the effects of ozonation by-products are largely unknown. Use of ultraviolet radiation has been found effective against bacteria in water, but is less effective against viruses and has no effect on cysts and worms. In addition, alternative disinfectants do not provide the residual protection of chlorine-based treatment; they must be used in combination with chlorine or chlorine derivatives to provide a complete disinfection system.
Lead is a naturally occurring metal. Exposure to lead in the United States is relatively widespread, because the metal was commonly used in many industries prior to the 1970s. Exposure to even low levels of lead can cause severe health effects in humans.
SOURCES OF LEAD EXPOSURE.
Mined along the eastern seaboard since 1621, lead created an important industry, providing bullets, piping, and a base for paint. Because of its malleability, it was valued as a conduit for water. The use of wallpaper steadily declined with the almost universal use of paint, not only for protecting surfaces, but also for interior decorating. "White lead" paint was sold as the best thing to use on interior and exterior surfaces. In cities teeming with millions of new immigrants, the glossy, durable finish of white lead-based paint meant walls could be easily washed. In 1922 a General Motors researcher discovered that the addition of lead to automobile fuel reduced the "knocking" that limited power and efficiency in car engines.
Many structures are still covered by old lead paint. Nearly three-quarters of all U.S. homes constructed before 1980 contain some lead paint. The EPA reports that lead paint poses little danger if stable. But when renovations are made that involve sanding or stripping paint, the old paint may become hazardous. Certain ceramics and crystal ware, especially those made in foreign countries, still contain unacceptable levels of lead. In 1996 researchers announced that ingredients used to manufacture some miniblinds could be toxic to humans because they contain lead. Lead can be found in many other places as well, including weights used for draperies, wheel balances, or fishing lures; seams in stained-glass windows; linoleum; batteries; solder; gun shot; and plumbing. Test kits and laboratories that test for lead can now check questionable items and locations for the presence of the heavy metal.
Most of the lead in water comes from lead pipes and lead solder in plumbing systems. A 1992 EPA report revealed that 20 percent of the nation's large cities exceeded government limits for lead in drinking water. By 1993 all large public water-supply systems were required to add substances such as lime or calcium carbonate to their water lines to reduce the corrosion of older pipes, which releases lead.
REDUCING LEAD EXPOSURE.
As early as the late 1890s medical reports concerning problems with lead began to appear. In 1914 the first U.S. case of lead poisoning was reported, although the cause was undetermined. Scientists eventually began to link lead poisoning to lead paints and, as World War II ended, began to address the problem. In the mid-1960s medical reports documented the connection of lead poisoning to both auto emissions and paint.
In 1971 Congress passed the Lead-Based Poisoning Prevention Act (PL 91-695), restricting residential use of lead paint in structures constructed or funded by the federal government. The phasedown of leaded fuel in automobiles began in the 1970s. This effort was not to safeguard health but to protect cars' catalytic converters, which were rendered inoperable by lead.
In an effort to protect families from exposure to the hazards of lead-based paint, Congress amended the Toxic Substances Control Act (TSCA; PL 94-469, 1976) in 1992 to add Title IV, entitled "Lead Exposure Reduction." Title IV directs the EPA to address the general public's exposure to lead-based paint through regulations, education, and other activities. A particular concern of Congress and the EPA is the potential lead exposure risk associated with housing renovation. The law directs the EPA to publish lead hazard information and make it available to the general public, especially to those undertaking renovations.
Also in 1992 Congress passed the Residential Lead-Based Paint Hazard Reduction Act (PL 102-550) to stop the use of lead-based paint in federal structures and to set up a framework to evaluate and remove paint from buildings nationwide. In 1996 Congress once again amended the TSCA, adding section 402a to establish and fund training programs for lead abatement and to set up requirements and training of technicians and lead-abatement professionals.
BLOOD LEAD LEVELS.
Lead is highly toxic, causing harm to the brain, kidneys, bone marrow, and central nervous system. Levels as low as ten micrograms of lead per deciliter of blood can have serious health effects in infants, children, and pregnant women. (See Figure 8.1.)
Lead is a cumulative poison. For people who are exposed to it every day, over time, it begins to accumulate in the body. At very high levels of exposure (now rare in the United States), lead can cause mental retardation, convulsions, and even death. More commonly, exposure occurs at very low levels over an extended period of time.
The Centers for Disease Control and Prevention (CDC) monitors blood lead levels (BLLs) of children and adults. Since the 1970s the concentrations of lead measured in blood samples of children aged five and under have declined dramatically. (See Figure 8.2.) However, the EPA's Draft Report on the Environment 2003 notes that lead poisoning is still a "serious environmental hazard in young children in the U.S." This is particularly true for urban areas. The EPA reports that in 2001 slightly more than 10 percent of the children screened for lead in Chicago had elevated blood levels of the metal. The percentage has fallen dramatically since 1996 when it exceeded 25 percent. On a nationwide basis the EPA estimates that approximately 2 to 3 percent of children have elevated BLL.
Many scientists believe that the federal standards for exposure should be lowered, and, in fact, some researchers believe there is no safe level for lead. The CDC believes that effects on the central nervous system of children begin at ten micrograms per deciliter, and the greater the BLL, the higher the risk. The CDC recommends that if many children in a community have BLLs above ten micrograms per deciliter, community-wide lead poisoning prevention activities should begin. The Occupational Safety and Health Administration requires that a worker be removed from a workplace if his or her BLL reaches 50 micrograms per deciliter, although two Harvard School of Public Health studies released in 1996 found kidney damage and hypertension correlated with lead levels in bone below ten micrograms per deciliter.
DOES LEAD CONTRIBUTE TO DELINQUENCY?
A 1996 University of Pittsburgh Medical Center study of 800 male public school students found that, even after taking into account other predictors of delinquency, such as socioeconomic status, boys with higher lead levels were more likely to engage in antisocial acts. A direct relationship was found between the amount of lead in boys' leg bones and reports from parents, teachers, and the children themselves of criminal or aggressive behavior.
The United States is the largest producer of fertilizers for domestic use and export, and American farmers are the most productive in the world, producing crops for domestic demand as well as for export to other countries. Agriculture exists in every state, but is concentrated in the Midwest. Although many different crops are farmed in the United States, corn, soybeans, wheat, and hay account for 75 percent of total crops in 2002. (See Figure 8.3.)
The U.S. Department of the Interior defines a fertilizer as any substance applied to soil to enhance its ability to produce plentiful, healthy crops. Fertilizers are natural or manufactured chemicals that contain nutrients known to improve the fertility of soils. Nitrogen, phosphorus, and potassium are the three most important of these nutrients; some scientists also consider sulfur a major nutrient for plant health. The EPA estimates that 90 percent of all fertilizers used contain nitrogen, phosphorus, and to a lesser extent, potassium.
The use of fertilizers sky-rocketed following World War II. Between 1960 and 1980 fertilizer use increased from approximately seven million tons per year to nearly 23 million tons per year. Fertilizer use declined during the 1980s, but then began to increase again, exceeding 20 million tons per year by the year 2000. The USGS estimates that approximately 12 million tons of nitrogen are applied to the land each year from commercial fertilizers. An additional seven million tons of nitrogen are applied as manure. These two sources are blamed for most of the nitrogen entering watersheds across the country.
Overfertilization of crops can cause excess chemicals to leach into surface and groundwater. Runoff of rain and irrigation waters washes nutrients (like nitrogen) into streams, rivers, and lakes. Excessive nutrients are a problem in surface waters because they cause conditions called eutrophication and hypoxia. Eutrophication occurs when nutrients stimulate the rapid growth of algae and aquatic plants. When these plants and algae die, bacteria in the water decompose them. This depletes the amount of dissolved oxygen in the water—a condition called hypoxia. Fish and other aquatic creatures require dissolved oxygen to live and thrive. Hypoxic areas become "dead zones" in the environment.
Nitrate (NO3) is a common form of nitrogen found in water. The EPA has monitored the nitrate load in the country's major rivers since the 1950s. The data show a disturbing trend, particularly in the Midwest, where fertilizer use and soil erosion rates are high. The nitrate load in the Mississippi River increased from approximately 250,000 tons per year in the early 1960s to approximately one million tons per year in 1999. The result has been the development of a massive hypoxic area near the mouth of the river in the Gulf of Mexico. Figure 8.4 shows how this area grew in size between 1985 and 2002. The data reflect midsummer measurements, because that is the time of year when hypoxia is at its worst.