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What's
in a Pesticide?
Normally,
a pesticide is thought of as a product that can be purchased in
stores and used as part of a service to kill pests-the insecticide,
weed killer, fungicide or wood preservative. Unfortunately, these
chemicals are not that simple. Pesticide products, particularly
wood preservatives, contain a number of different toxic materials,
some of which are secret because they are considered confidential
business information.
Active
Active ingredients are by nature biologically and chemically active
against the target pest, be it an insect or fungus. By definition,
these materials kill living things.
Inert
Inert ingredients are often as toxic as the active ingredient, although
the law defines these materials as "secret business information."
Inerts, often petrochemicals like benzene, toluene or xylene, generally
make up t he largest percentage of the ingredients of a pesticide
product. They form the solution, dust, or granule in which the active
ingredient is mixed.
Contaminants
Contaminants and impurities are often a part of the pesticide
product and are responsible for the product hazards. Dioxin is a
contaminant in pentachlorophenol, created as a function of the production
process.
Metabolites
Metabolites, often more hazardous than the active ingredients, are
breakdown products which form when the pesticide mixes with air,
water, soil or living organisms.
Penta 45%
Creosote 13%
Arsenicals 42%
Synergism
Synergism refers
to a greater-than-additive impact when a person is exposed to more
than one chemical at a time. This can be thought of as teamwork among
the chemical actors. If, in order to cause cancer, you need to cause
a mutation in a cell and cause t he mutated cell to grow fast, then
a chemical that just causes mutations or one that just causes precancerous
cells to grow faster won't cause many cancers alone. Together, however,
they will add up to a potent carcinogen.
* This
teamwork is particularly important in the case of wood preservatives,
which are all complex mixtures of toxic ingredients. Some ways that
wood preservative ingredients act synergistically are known:
* The
toxicity of CCA to water fleas and algae has been found to be greater
than what would be predicted from the toxicity of the individual
metals.
* Several
of polycyclic aromatic hydrocarbon constituents of creosote are more
potent carcinogens when present together than alone.
* The
mechanism by which dioxins cause cancer is known to be one that
promotes growth of cells containing a mutation. Therefore, it is
most potent when in combination with a material that causes mutations.
Among such materials are penta and its metabolites.
* Creosote
may be synergistic with other chemicals that cause photosensitivity.
* A number
of researchers have found that arsenic compounds tend to reduce
the effects of selenium. Selenium plays a role in copper homeostasis
and detoxification. So arsenic probably increases the toxicity of
copper.
* Exposure
to pentachlorophenol makes hexachlorobenzene more potent in producing
porphyria (liver disease).
* Hexachlorobenezene
increases the potential for the thymic atrophy (immune system damage)
and body weight loss (wasting) caused by dioxin.
The
Endocrine Disruptors
Chemicals that disrupt the endocrine system wreak havoc
Hormones
are chemicals made by the body that help control the body's functions.
They are present in minute quantities. Certain other chemicals may
be mistaken for hormones by the body, and disrupt the systems controlle
d by the hormones. In particular, some chemicals are mistaken for
the female hormone estrogen. These estrogen mimics interfere with
the reproductive system, causing infertility, malformed sexual organs,
and cancer of sensitive organs. Creosote and penta interfere with
hormone function. Creosote contains ingredients, benzo(a)pyrene
and higher phenols, considered to be endocrine disruptors.
Although
many chemicals, including pentachlorophenol and its contaminants-
polychlorinated dibenzo-p-dioxins, dibenzofurans, and hexachlorobenzene-are
considered endocrine disruptors, evidence is rarely as strong for
most chemicals as it is for penta. Exposure to penta may result
in adverse reproductive effects that are associated with changes
in the endocrine gland function and immunological dysfunction. A
number of women with histories of spontaneous abortion, unexplained
infertility and mens trual disorders had elevated levels of pentachlorophenol
and/or lindane in their blood.
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The Chemical
Actors
Three chemical
mixtures are common to wood preservation - pentachlorophenol, creosote,
and arsenicals (primarily copper chromium arsenate or CCA). A fourth,
copper naphthenate is commonly regarded as an alternative. These chemicals
all have serious a adverse impacts on human health and the environment.
The chemicals
and their toxicology
In order for a
chemical to protect wood poles from insects and fungi for 40 years
or more, it must be toxic to a wide range of organisms and very persistent
to all living organisms. Unfortunately, those very characteristics
make these chemicals dangerous when released into the environment.
Pentachlorophenol
(penta) is a chlorinated aromatic hydrocarbon closely related
to other chlorophenols, hexachlorobenzene, polychlorinated dibenzo-p-dioxins
and furans. All of these elements are found in commercial grade
penta, along with secret "inert" (but biologically and chemically
active) ingredients.
Creosote
is a complex and variable mixture consisting of approximately 75%
polycyclic aromatic hydrocarbon derivatives of coal tar, including
anthracene, naphthalene, phenanthrene, acenaphthene, fluorine, and
pyridine.
Arsenicals
are mixtures of metallic salts, including arsenic pentoxide. For
example, Copper Chromium Arsenate (CCA) is a mixture of arsenic
pentoxide, chromic acid, and copper or cupric oxide, plus secret
"inert 8; ingredients, in proportions that vary with the particular
product. The chromium in CCA occurs in the more toxic hexavalent,
or chromium (VI), form. Copper Naphthenate contains about
20% copper salts of naphthenic acids-which consist of an unknown
mixture of certain petroleum by-products and contaminants-and about
80% unknown secret ingredients.
The chemicals'
affect on human health
Absorption
The oil-based wood
preservatives, pentachlorophenol, creosote, and copper naphthenate
are all easily absorbed through the skin, as well as through inhalation.
The arsenicals are less easily absorbed through the skin, but are
readily absorbed by inhalation of dusts or smoke from burning treated
wood. Children may ingest all of the chemicals in soil contaminated
by leaching from poles.
Acute health
effects-Effects of short term exposures to large quantities
All wood preservatives
used to treat poles have high acute toxicity. They all attack the
skin and nervous system. They may all cause nausea and vomiting. They
can all be fatal in single large doses.
Chronic health
effects-Effects of long term exposures to small quantities
Wood preservatives
are known to cause a variety of chronic health effects, though copper
naphthenate is mostly untested. Some of the known health effects are:
- Impair
the immune system: creosote, penta, arsenicals.
- Interfere
with reproduction: creosote, arsenicals, penta.
- Cause
birth defects: penta, arsenicals.
- Cause
cancer (EPA's cancer classification): creosote (B1 - probable
human carcinogen), penta (B2 - probable human carcinogen), arsenicals
(A-known human carcinogen).
- Cause
genetic mutations: arsenicals, penta, creosote, copper naphthenate.
- Interfere
with hormone function: penta, creosote.
Cancer
Some chemicals can increase the chance of cancer in humans by causing
changes in cells that may lead to cancer, by facilitating the growth
of cancer cells, or by inhibiting immune responses that arrest the
growth of precanc erous cells. Because of the way cancer starts
and progresses, any quantity of a cancer-causing substance increases
the chance that the exposed person will get cancer. EPA assigns
ratings to substances that cause cancer ranging from A (human carcinogen)
to E (evidence of non-carcinogenicity). Creosote, penta, and the
arsenicals all cause cancer. EPA's cancer classifications are as
follows: creosote-B1 (probable human carcinogen), penta-B2 (probable
human carcinogen), arsenicals-A (human carcinogen) .
An increased
risk for cancer has been demonstrated in animals exposed to coal-tar
creosote. The International Agency for Research on Cancer has determined
that creosote is probably carcinogenic to humans (Group 2A).13 EPA
has determined that cresols are p ossible human carcinogens.14 Animal
studies show that cresols, a component of creosote, may increase
the ability of some carcinogenic chemicals to cause tumors.15 Dermal
exposure to creosote can increase the risk of cancer from other
agents.16
The studies
indicating that human exposure to pentachlorophenol products causes
cancer go back to 1978.16 They include studies of occupational exposure
in the lumber and sawmill industry linking penta with acute leukemias,
Hodgkin's and non-Hodgkin? 146;s lymphomas and multiple myelomas.18
EPA classifies
pentachlorophenol as a probable human carcinogen (B2). It finds
the sole human study examined by the agency to be inadequate. EPA
bases the B2 classification on animal studies that find that two
different preparations of pentachlorophenol c ause statistically
significant increases in incidences of biologically significant
tumor types in both male and female mice: hepatocellular adenomas
and carcinomas, adrenal medulla pheochromocytomas and malignant
pheochromocytomas, hemangiosarcomas, and hemangiomas. Other animal
tests and reviews by other agencies support the conclusion of carcinogenicity.19
The hexachlorobenzene
and hexachlorodibenzo-p-dioxin contaminants in penta are also carcinogens.
Agriculture Canada has concluded that the combined evidence from
epidemiological studies on humans with mixed exposures to chlorophenols,
dioxins, or pesticid es contaminated with these chemicals suggest
that occupational exposure to chlorophenols or phenoxy herbicides
increases the risk of three kinds of cancer: soft tissue sarcoma,
Hodgkin's lymphoma, and non-Hodgkin's lymphoma.20 National Toxicolog
y Program studies show the penta metabolite pentachloroanisole to
be carcinogenic in rats and mice.21 EPA classifies arsenic as a
class A, or known human carcinogen. Arsenic ingestion or inhalation
has been reported to increase the risk of cancer, especially in
the liver, bladder, kidney, and lung.22 Chromium (VI), found in
some arsenicals (such as CCA) i s also classified as a known human
carcinogen.23
Effects
on the Immune & Nervous System When a chemical interferes
with the body's immune system, it makes a person more susceptible
to disease. Creosote, penta, and the arsenicals all interfere with
the body's defenses against disease.
Laboratory studies
find that technical grade penta causes immune suppression in animals,
which has been linked to dioxins contained in penta.24
Evidence in
both animals and humans suggests that arsenic suppresses the immune
system.25 Neurotoxic chemicals affect the nervous system in various
ways.
Both arsenic
exposure and penta exposure are associated with disturbances and
degeneration of nerves in the peripheral nervous system-causing,
for example, numbness and a sensation of "pins and needles."26
Reproductive
Toxicity and Teratogenicity Chemicals may interfere with reproduction
in different ways-by causing infertility, death of the fetus (fetotoxicity),
low birth weights, or birth defects. Creosote, penta, and the arsenicals
all interfere with reproduction, and/or cause birth defects.
Mice fed benzo(a)pyrene,
one of the components of coal tar creosote, during pregnancy had
difficulty reproducing, and so did their offspring.27
Experiments
in rats and mice have shown creosote to be teratogenic.28 Birth
defects have been seen in livestock exposed to wood treated with
coal-tar creosote.29
Animal experiments
indicate that chronic exposure to pure pentachlorophenol affects
reproduction and induces birth defects.30 EPA has concluded that
penta and possibly its hexachlorodibenzo-p-dioxin (HxCDD) contaminants
cause birth defects and fetotoxic e ffects in test animals.31 Reported
adverse effects in fetuses from penta exposure include distorted
sex ratios, increased incidences of resorbed embryos, skeletal anomalies,
subcutaneous edema (excessive fluid), reduced survival, and reduced
growth. Sever al studies of rats and mice have shown birth defects
due to the penta contaminant HCB, including changes in rib development
and cleft palate formation in rats. Kidney malformations and decreased
body weight were also noted.32
Ecological
Effects
Persistence/bioaccumulation/bioconcentration
potential
Persistence
refers to the length of time a chemical remains in the environment
before it breaks down into other chemicals. It may break down by
chemical action, with the help of the sun's energy, or through biological
decomposition. Some chemicals br eak down into more toxic chemicals,
so lack of persistence does not always mean that the toxic effects
disappear. Bioconcentration refers to the way certain chemicals
become more concentrated in biological tissues than in their surrounding
environment. Th is is particularly important for aquatic organisms
which live in polluted water-if they take in a chemical faster than
they can excrete or metabolize it, it will concentrate in them.
Bioaccumulation refers to the accumulation of a chemical in higher
and higher concentrations from one step in a food chain to the next.
Although small
amounts of toxic metals are excreted by organisms, doses of arsenic
and associated metals that are found in some environments as a result
of contamination from wood preservative are high enough to accumulate
in plants and animals. Arsenic b ioconcentrates in aquatic organisms-in
freshwater organisms up to 17 times background levels, and in marine
oysters 350 times background levels.34
Some components
of creosote have been found to bioaccumulate and bioconcentrate
in aquatic and terrestrial systems.35
The dioxin contaminants
in penta are persistent and bioaccumulative. The only known process
by which dioxins break down in the environment is photolysis (photodegradation).36
Dioxins are strongly partitioned into the organic components of
the environment. In other words, if there are living things in water
contaminated with dioxin, the dioxin will be rapidly taken up by
living tissue. In fact, sampling for dioxin in aquatic systems uses
fish as concentrators of the toxics.37
Leaching
potential and environmental fate
The way
a chemical moves in our environment affects the likelihood of our
being exposed to it. Some chemicals attach themselves to soil particles
and are more likely to be carried by heavy runoff into streams than
to leach into groundwater. Some dissolve in water and leach quickly
through the soil. Others may be found only in organic matter. Often
the behavior of chemicals depends on certain aspects of the environment,
especially acidity (pH) of the soil or water.
Studies on the
movement of wood preservatives from poles have found that they move
from poles into soil and from the soil into aquatic ecosystems.
The mechanisms by which the various chemicals move are different.
Some of the materials are water soluble an d are transported as
dissolved salts. Others are adsorbed onto soil particles and are
carried into streams as suspended particles in heavy rainfall. Once
in an aquatic setting, the soil particles provide a steady source
of contaminant.38
The degree to
which arsenicals leach is strongly dependent on pH. Much more chemical
leaches into acid water than into neutral or basic water. Therefore,
we should expect arsenicals to leach more in environments high in
soil humic acids or where acid precipitation has affected the pH
of the soil.39 Penta, on the other hand, is more mobile in neutral-to-basic
soils.40
Spontaneous
abortion rates were increased among workers exposed to arsenic,
compared to controls. In rodent tests, arsenic increased fetal mortality
and birth defects, and increased the ratio of males to females in
mice.33
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