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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 SubstancesDioxin, 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.
DioxinA 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.
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MercuryMercury 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
LeadEven 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.
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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 BioaccumulationAn 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.
PersistenceMost 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
BiomagnificationNormally, 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
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