[ Report Home | Previous Page | Next Page ]

Poisoning Our Future

Section I: Toxic Chemicals Threaten Public Health and the Environment

Report Home
Over the last fifty years, society has become increasingly dependent on chemical use. Tens of thousands of synthetic chemicals are being used and produced in the U.S. today and new chemicals are added to the market every year. Evidence links many chemicals that are commonly used and released in high volumes by U.S. industries to serious public health and environmental problems.

But scientific evidence and public health case studies are also showing us the risks associated with chemicals that are not always used in large amounts. A dangerous legacy is being created by substances that are often used or released in very small quantities--some of them simply produced as industrial by-products. Even at low levels, however, these substances threaten humans and wildlife today and for generations to come.

During the 1980s, mothers who had eaten PCB-contaminated fish from Lake Michigan gave birth to children with lower weights and smaller head circumferences. In 1995, children whose mothers had eaten modest amounts of PCB-contaminated fish from Lake Ontario showed behavioral and neurological problems.2 PCB production has been banned in the U.S. since 1976, yet these toxic substances are still showing up in humans and animals today.

As the result of a toxic chemical spill from nearly two decades ago, alligators in Lake Apopka, Florida have experienced severe reproductive damage, taking a devastating toll on their population numbers. This chemical spill introduced toxins, including a close relative of DDT, that are still circulating in the lake’s food web today.3

Substances like dioxins, mercury, lead and PCBs pose a significant threat to public health and the environment because they are highly toxic even in minute quantities, remain in ecosystems for long periods of time and accumulate in the tissue of animals and wildlife. These “persistent and bioaccumulative substances” often increase their impact as they move up the food chain, and at very low levels, create a legacy of damage for months, years, and even decades after they are released into the environment.

The Most Dangerous Substances

Dioxin, lead, mercury, and PCBs are some of the most well-known persistent bioaccumulative toxins. These substances can cause health effects ranging from cancer, to birth defects, to hormone disruption. And the risk of developing severe health problems is amplified by the tendency of these chemicals to persist and bioaccumulate. The problem is frightening, but quite simple: the longer a substance persists in the environment, the greater chance humans and other species are exposed to it; the more a substance bioaccumulates, or builds up in human and animal tissue, greater exposure to higher levels of the dangerous substance.


A growing problem of toxic chemical use and production is the release of dangerous substances formed as by-products of other chemical or industrial processes. The most striking example of this is a group of substances known as dioxins—released into the environment primarily through combustion of chlorine-containing chemicals and other chlorine chemistry processes. Dioxin and dioxin-like substances are observed to cause toxic effects at extremely low levels . One of the dangers of dioxin is the increased incidence of cancer associated with its exposure.

Dioxin compounds are also some of the most well known endocrine-disrupters: compounds that can have an effect at low levels of exposure by mimicking hormones in the endocrine system. A U.S. mother’s breast milk can contain dioxin which can impair immune system function, neurological development, learning behavior, and the reproductive system of infants. The average breast feeding infant is subject to daily doses of dioxin 20-60 times higher than that received by the average adult.4

Box 1.10 The Ban on Lead in Gasoline

“The reason there is so much less lead in the environment- and in children’s blood-is that lead has been almost entirely eliminated from the manufacture of gasoline. If you don’t put something into the environment, it isn’t there.”
-- Barry Commoner, Making Peace with the Planet

Shortly after World War II the American automobile industry made the decision to begin producing heavier cars with more powerful engines. The shift to bigger, heavier cars necessitated a change in the type of gasoline needed to power these vehicles, specifically the addition of tetraethyl lead. Between 1950 and 1968 the average lead content of U.S. gasoline increased by 35 percent. By 1970 cars and trucks were responsible for 80 percent of lead air emissions in the U.S.

Because of the serious environmental and health impacts of the high amounts of lead pollution, in 1975 the U.S. banned the use of lead in gasoline. Although the decision was met with great opposition from the automobile industry, alternatives to using leaded gasoline were quickly adopted.

Between 1975 and 1987 total annual lead emissions decreased by 94 percent and airborne concentrations at national test sites by decreased by 92 percent. The average lead levels in children’s blood decreased by 37 percent between 1976 and 1980. The successes associated with leaded gasoline phase-out show that it is possible to reduce pollution quickly and sharply by reducing the substance at the source. Sadly, this is one of very few such success stories. And, unfortunately, other sources of lead pollution still present a significant risk.


Mercury is the pollutant most responsible for fish consumption advisories in the U.S. Thirty-nine states have issued mercury advisories, in a total of 50,000 water bodies across the country. Thirteen states and Washington DC have issued advisories declaring fish in every lake in their state unsafe to eat.5 It takes only a fraction of a teaspoon of mercury to contaminate an entire lake to the point where fish are unsafe to eat. It has been estimated that 40 percent of Americans are eating fish contaminated with unsafe levels of mercury. Also, when tested, the average can of tuna contained mercury exceeding EPA’s recommended safe levels for adults.6 By far, the largest known sources of mercury pollution are coal and oil-fired power plants.

Mercury has been linked to a number of health effects including central nervous system damage and kidney damage. Exposure to some forms of mercury, like methyl mercury, via eating fish can cause developmental effects—children born to women with high levels of methyl mercury in their bodies have exhibited mental retardation, blindness, and cerebral palsy.7


Even at low levels, childhood lead exposure has been known to cause delays in normal physical and mental development and deficits in hearing and learning abilities, often represented as loss of “IQ.” Chronic exposure has been linked to human cerebrovascular, kidney, reproductive, and neurological disease. Exposure of pregnant women can cause premature birth, low birth weights, or abortion.8 Although lead has been banned in gasoline since 1975, major sources of this extremely persistent substance still pollute the environment, including incineration, lead production, and mining. (See Box 1)

Box 2. The Ban on PCB Production

In light of growing evidence of PCB toxicity and persistence, the production of PCBs was banned in the United States in 1976. By 1980, measurable loads of PCBs in wildlife had declined -- in fresh- water fish by 56 percent and in starlings by 86 percent. The percentage of the human population with relatively high PCB loads declined by 75 percent.

Unfortunately, the chemicals’ persistence in the environment and their ability to bioaccumulate means that decline has not led to disappearance of the chemicals or their toxic effects. Although they are banned for production in the U.S., products containing PCBs are still in wide circulation and provide continuing sources of exposure for humans and other animals.

Polychlorinated Biphenyls (PCBs)9

Polychlorinated Biphenyls (PCBs) were developed in the 1930s and found uses in a wide variety of products, from electrical transformers and rubber products to stucco, paints, and varnishes. Although reports of toxic effects on workers surfaced as early as 1936, industries continued to find more and more uses for the chemicals.

PCBs have been linked to cancer, immune system and reproductive system damage, and other health problems. Based on PCBs’ ability to persist in the environment and bioaccumulate in the mother’s breast milk, scientists have estimated that one of every 20 babies born in the U.S. today are exposed to levels sufficient to cause neurological impairment. PCBs are still found in the tissues of animals far from industrial sources such as polar bears in the Arctic Circle.

Although they are now banned for production in the U.S., products containing PCBs are still in wide circulation and provide continuing sources of exposure for humans and other animals. In addition, close relatives of PCBs are still widely produced, used, and released to the environment. (See Box 2 )

Substance Health Effects Environmental Impacts Common Uses Major Sources
Mercury central nervous system damage, kidney damage; prenatal exposure leads to mental retardation, blindness, cerebral palsy biomagnification in aquatic ecosystems; most frequent contaminant necessitating fish advisories; linked to decline of Florida panther, wood stork, as well as other fish-eating species fluorescent lamps, thermometers, dental amalgam, switches, thermostats, relays, laboratory solutions, specialized batteries, chlorine production; (banned from use in Latex paint in 1991) coal combustion, chlorine alkali processing, waste incineration, metal processing
Lead hearing deficits, learning disabilities, cerebrovascular, reproductive, and neurological disease; some compounds can cause cancer; in pregnant women can lead to premature birth, low birth weight, abortion attaches to dust in air and is carried long distances; attaches to insoluble salts in soil; bioconcentrates in shellfish such as mussels; poisons waterfowl from lead shot and fishing weights lead-acid batteries, ammunition, glass, covering for cables, building construction materials, plumbing, pigments, pesticides, solder, radiation shielding; (now restricted in gasoline and paint; some restrictions on lead in plumbing pipes) lead and zinc smelting, non-municipal incineration, aircraft fuel, other fuel burning, copper and steel mills, glass pressing and blowing
Dioxin and Dioxin-like Compounds (Furans, some PCBs or PBBs) prenatal effects on immune system and reproductive system function, learning behavior; postnatal effects on immune system, chloracne, endocrine disruption; may cause cancer; suspected in decreased fertility persist in the environment for decades; primarily thought to enter food chain through atmospheric deposition; cause reproductive effects in wildlife populations (e.g., seals, mink) dioxin and furans: by-products of combustion and chemical processes. PCBs: produced for dielectrics, hydraulic fluids, plastics, paints. PBBs: produced as flame retardants; (intentional production of PCBs and PBBs has been discontinued) waste incinerators, fuel-burning, cement kilns, metal production, chemical manufacturing processes for wood preservatives and chlorine-bleached wood
Hexachloro-benzene (HCB) damage to liver, kidneys, neurological system, and immune system; probable human carcinogen and endocrine disrupter; in pregnant women, may damage fetus bioaccumulates in fish, marine mammals, birds, lichens, and animals that can eat lichens; builds up in wheat and vegetables. was used in many chlorine chemistry processes; was most often used to make other compounds; was also used as wood preservative, additive in explosives; (no longer direct commercial uses, but still produced as a by-product of chemical production) coal combustion, air and water discharges from chemical manufacturing processes, application of pesticides that include it as a contaminant, waste incineration
Polycyclic Aromatic Hydrocarbons (PAHs) red blood cell damage, immune system suppression, developmental and reproductive effects, suspected to cause cancer capable of long distance transport in air; remain in soil; carcinogenic and reproductive effects in animals most are by-products of burning, and have no use; some are produced deliberately and used in medicines and production of dyes, plastics, and pesticides found in soot; consumer and commercial solvent use; produced from fires (inc. residential wood combustion), volcanoes, industrial products and waste, waste oils, and wood-treating residues; pulp and paper production
Triazine Herbicides possible human carcinogens and endocrine disrupters; cardiovascular, liver, kidney, and thyroid damage, retinal and muscular degeneration, and tremors from chronic high exposure persistent, but not very bioaccumulative. very mobile in soil--wash into waterways from heavy rains; commonly found in drinking water near farming areas agricultural pesticides--most commonly used on field corn, sorghum, and soybeans; also used on turfs and lawns, pineapples, sugarcane, wheat, and several deep-rooted crops. almost all herbicides produced will eventually be released--sources include manufacturing facilities, their distributors, farm use, and commercial and home use for lawn care
Certain Pesticides (Aldrin/Dieldrin, Chlordane, DDT, DDE, DDD, Endrin, Heptachlor, Kepone, Lindane, Mirex, Toxaphene) nervous system damage, endocrine disruption, neurological effects, cancer; damage to liver, kidney, immune system, and lungs linked to declining wildlife populations including birds, fish, and alligators used as agricultural insecticides and rodenticides; also other industrial uses (manufacture of most of these pesticides has been banned in the U.S., but use of old supplies continues, as well as release from waste disposal sites and other sources) almost all pesticides produced will eventually be released-- major sources include manufacturing facilities, farms, businesses, and homes

Persistence and Bioaccumulation

An obvious way of avoiding exposure to toxic chemicals is to reduce the amounts of these substances entering the environment. However, some substances have characteristics that increase the likelihood that people will be exposed to them, even if they are released into the environment in very small amounts.

Persistent Bioaccumulative Toxins (PBTs) persist, or remain in the environment for a relatively long time without degrading to other substances. They also bioaccumulate, building up to a higher concentration in organisms than in the surrounding environment. Both persistence and bioaccumulation increase the likelihood of exposure: if Chemical A remains longer in the environment than Chemical B, then all other things being equal, people are more likely to be exposed to Chemical A over time. Likewise, if Chemical A bioaccumulates and Chemical B does not, people will have a higher concentration of Chemical A in body tissue, even if both chemicals are present at the same levels in the environment and people received their exposure to both chemicals the same way, such as drinking water containing both chemicals.

In general, greater exposure means a greater potential for harm, so PBTs are chemicals of concern for all population groups. However, children are under greater threat for two reasons: First, because children are still developing, their body systems are more vulnerable. Second, because of their smaller size and more active lifestyles, they generally experience greater exposure to toxic chemicals per pound of body weight than adults, even without the added potential for exposure from PBTs. Children breathe 30 to 50 percent more air per pound of body weight than do adults, and they are also more likely than adults to be exposed to contaminants in soil.

Persistence and bioaccumulation are also of particular concern for chemicals that are harmful to developing fetuses. Thus, a woman can be exposed to a PBT released into the environment months or even years previously, and pass the chemical onto her unborn child.


Most chemicals degrade, or break down into other substances, when they are exposed to ultraviolet radiation from the sun, as well as heat, oxygen, water, organisms in water or soil, or other chemicals present in the environment. For example, consumer products labeled “biodegradable” are supposed to naturally break down in the environment into other (presumably) non-toxic substances. “Persistence” is a measure of the speed of degradation, and is usually measured by a chemical’s half-life in air, water, soil, or sediment. The half-life is the amount of time required for half the original amount of chemical to degrade into other substances.

Half-lives can range from seconds, in the case of extremely reactive chemicals, to years, in the case of some pesticides, to indefinitely for metals. A substance’s persistence or half- life is usually given for a single environmental medium. The value can be vastly different in air, fresh water, salt water, sediment, and soil and can differ depending on the presence or absence of oxygen. Persistence is usually reported for the medium in which most of the chemical typically ends up, or the one in which there is the greatest potential for exposure in a given situation. Substances with half-lives of months are generally agreed to be extremely persistent.

Reliable, measured half-life data exist for some well-studied chemicals in given situations, such as PCBs in fresh-water sediment. However, many more substances have incomplete data at best, and most have no data at all. In the absence of data, industry and regulators rely on modeling to provide rough estimates of half-lives. These models use linkages to chemicals already tested such as chemical properties and elements of molecular structure. While it is usually preferable to have measured data for predicting persistence, the models may provide enough information to act as a screening tool for selecting chemical/media pairs for collecting experimental data.

Although persistence generally refers to a single substance, many substances degrade into chemicals just as toxic, persistent, or bioaccumulative than the original substance -- or even worse in the case of some chemicals such as nonylphenol ethoxylates. Unfortunately, most persistence measurements do not include the persistence of degradation products, and therefore may not give a true indication of the potential for harm from a release of a given chemical into the environment.

Bioaccumulation, Bioconcentration, and Biomagnification

Normally, the concentration of a chemical in a person’s bloodstream or tissue won’t be greater than the concentration in the surrounding environment. The body usually metabolizes or removes most substances quickly enough to keep them from building up. However, some chemicals get stored in fatty tissue and will keep accumulating as people are exposed to them. This property is called bioaccumulation. It is important because levels of environmental pollution may not be high