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.
ContaminantsContaminants 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.
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
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-
The Chemical ActorsThree 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 toxicologyIn 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
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:
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
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