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Poison Poles - A Report About Their Toxic Trail and Safer Alternatives
Appendix A: Chemicals At A Glance



copper naphthenate

Identity And Uses 

Ingredients, including contaminants, inerts, and by-products

Pentachlorophenol (penta) is a chlorinated aromatic hydrocarbon, closely related to other chlorophenols, hexachlorobenzene, polychlorinated dibenzo-p-dioxins and furans, all of which are found in commercial grade penta, along with secret "inert" ingredients. Pure pentachlorophenol can be produced in a laboratory, but the commercial products contain these contaminants. We address here penta as it exists in the environment--with contaminants. 

Trade names

Penta, Penchlorol, Chlorophen, Pentacon, Penwar are some of penta's trade names. 


In 1995: 39,734,000 gallons (8,588,000 gallons concentrate and 31,146,000 gallons solvent); 30,617,000 cubic feet of treated poles; 32,764,000 cubic feet of treated wood. 



Pentachlorophenol is readily absorbed by lung, skin and stomach. Workers handling penta or penta-treated wood receive the most significant exposure first through skin contact and second through the air. 

Clearing, detoxification, and metabolism

While much of it is excreted in urine, it accumulates in tissues, particularly muscle, bone marrow, and fat. 

Acute toxicity

Pentachlorophenol is very toxic, and is labeled with the signal word DANGER. There are about 50 known cases of poisoning from penta products, 30 of which have resulted in death. Immersion of a man's hand in a 0.4 percent penta solution for 10 minutes caused pain and inflammation.  Symptoms of mild penta poisoning include stuffy nose, scratchy throat, and tears in the eyes. Skin contact can produce contact dermatitis and chloracne. A person experiencing systemic poisoning by penta would show symptoms of profuse sweating and intense thirst, rapid breathing and heart rate, fever, abdominal pain, nausea, weakness, lack or coordination, dizziness, anorexia, and coma. 

Critical doses

The exact dose required to produce illness in humans is not known. It is a short jump from the "no effect" level to the "lethal" dose of pentachlorophenol. For example, at a dose of 80 milligrams per kilogram, no experimental animals died. At a dose of 100 milligrams 83% died and at 110 milligrams 100% died. 

Chronic health effects

The first report of chronic poisoning from pentachlorophenol was reported in California Health in June, 1970 in the case of a woman who had moved into a newly constructed home which had been treated with penta. She experienced rapid weight loss, weakening and tightening in her chest, and symptoms which were suspected to be asthma and bronchitis, which were relieved after she moved from the house. Exposure to penta has also been associated with aplastic anemia, leukemia, and other blood disorders. 

Organ damage 

Penta targets the liver, kidneys and central nervous system, with toxic effects occurring at low doses. Autopsies of victims of fatal exposures revealed changes in the brain, heart, kidneys, lungs, and liver. Liver damage has been documented in people living in homes treated with pentachlorophenol. Chronic exposure to pure pentachlorophenol causes acne and other skin diseases. 


Penta exposure is associated with peripheral neuropathy and other nerve damage. 

Reproductive toxicity and teratogenicity

Animal experiments indicate that chronic exposure to pure pentachlorophenol affects reproduction and induces birth defects. EPA has concluded that penta and possibly its hexachlorodibenzo-p-dioxin (HxCDD) contaminants cause birth defects and fetotoxic effects in test animals. 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. Several studies with 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.


Laboratory studies find that technical grade penta causes immune suppression in animals, which has been linked to dioxins contained in penta.

Critical doses

EPA has established a RfD for penta of 3X10-2 mg/kg/day, based on a NOAEL of 3 mg/kg/day and LOAEL of 10 mg/kg/day and an uncertainty factor of 100 to account for intra- and interspecies variability. These data are from the sole study EPA located for effects of chronic exposure. Liver and kidney pathology were the reported effects.


The studies indicating that human exposure to pentachlorophenol products causes cancer go back to 1978. They include studies of occupational exposure in the lumber and sawmill industry linking penta with acute leukemias, Hodgkin's and non-Hodgkin's lymphomas and multiple myelomas. EPA classifies pentachlorophenol as a probable human carcinogen (B2). The agency 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 cause 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. EPA estimates a cancer potency (slope factor) of 1.2X10-1 (mg/kg/day)-1 based on the incidence of hemangiosarcomas and pheochromocytomas in female mice. The hexachlorobenzene and hexachlorodibenzo-p-dioxin contaminants in penta are also carcinogens. Agriculture Canada has concluded that the combined evidence from epidemiological studies on human with mixed exposures to chlorophenols, dioxins, or pesticides 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.  National Toxicology Program studies showed the metabolite pentachloroanisole to be carcinogenic in rats and mice.


Some tests have indicated that pentachlorophenol and tetrachlorophenol can damage genes. A penta metabolite, tetrachlorohydroquinone, has also been shown to damage genes.

Endocrine disruption

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 menstrual disorders had elevated levels of pentachlorophenol and/or lindane in their blood.

Ecological Effects 

Pentachlorophenol and the contaminants found in penta products have immense ecological impacts. 

Bioaccumulation/bioconcentration potential

Under conditions of constant exposure as in aquatic organisms living in contaminated water, pentachlorophenol bioaccumulates as much as 10,000 times the background level.28 It may be taken up by plants from soil. In mammals, it may accumulate in the liver, kidneys, plasma protein, brain, spleen, and fat, until it is excreted unchanged in the urine. Pentachlorophenol is not expected to concentrate as it moves up the food chain, but the dioxin and dibenzofuran contaminants in penta products do bioconcentrate and bioaccumulate in the environment. Most of these contaminants found in an ecological system will be in animal fat. Dioxin contaminants may concentrate to 100,000 times the environmental level.

Leaching potential and environmental fate

Most wood treated with PCP solutions will "bleed", or move from the interior to the surface of the wood. Penta may evaporate from the surface of the wood into the air while some of the contaminants may not. About 48% of Pentachlorophenol will eventually end up in terrestrial soil; about 45% will end up in aquatic sediments; about 5.3% will end up in water; and about 1.4% will end up in air. After reaching soil, PCP is broken down by sunlight and bacteria, and can leave the upper soil layer by evaporation and leaching into groundwater. PCP degrades most rapidly anaerobic soils. Pentachlorophenol is moderately soluble in water. Concentrations of 1 to 1,000 milligrams will dissolve in a liter of water. Pentachlorophenol concentrations in natural waters may be higher, however, due to the presence of suspended solids. These solids provide a source of penta that continues to leach into water. Pentachlorophenol is moderately persistent in water. It may be degraded by sunlight or microorganisms or bind to sediments and suspended particles and does not evaporate to a significant degree. In water, biodegradation occurs with a half-life ranging from hours to days, with most biodegradation occurring at the surface. Penta has measured in the air of two towns were up to 0.93 and 7.8 ppt. PCP has been detected at very low levels in rivers and streams (0.01-16 ppb), surface water systems (1.3-12 ppb), and seawater (0.02-11 ppt). The compound has also been found in ground water in California, Oregon and Minnesota at concentrations ranging from 0.06 ppt to 0.64 ppb and in well water in Japan and Canada. It was found in a concentration that exceeded EPA's maximum contaminant level (MCL) in a public water supply well in the state of Washington. The HCB contaminant of penta was found to completely degrade to pentchlorophenol in hydrosoil samples. Evaporation was rapid on soil surfaces, but less so when it is mixed into the soil. Hexachlorobenzene has been found in well water in several states at concentrations ranging from 1 ppb to 5.6 ppb. It bioaccumulates to 570 times the ambient level in algae. The dioxin contaminants are extremely stable and resistant to degradation.


Acute ecological effects include the death of animals, birds, or fish, and death or reduced growth rate in plants. Penta may kill or defoliate plants and reduce germination of seeds. Pentachlorophenol has high acute toxicity to aquatic life, which increases as the pH of the water decreases. Chronic ecological effects of penta include reduced lifespan, reproductive problems, lower fertility, and changes in appearance or behavior. Cattle and other farm animals have ingested pentachlorophenol by chewing and licking outdoor wood structures, or from being housed in wooden pens that were treated with penta, causing sickness and death in some animals. In late 1976, about 100 Michigan dairy farms had herd health problems due to contact with penta-treated wood. Penta and contaminants were detected in the milk of two herds. Pentachlorophenol has high chronic toxicity to aquatic life. Penta is chronically highly toxic to cold and warm water fish and moderately toxic to other freshwater and marine organisms. Concentrations detected in rivers, streams, or surface water systems have been generally below lethal levels. Lethal levels have been exceeded during accidental spills. Japanese quail tolerated diets containing 200 ppm HCB, but had an LC50 of 568 ppm with the onset of signs at 3 days, indicating that moderate toxicity to the quail. In pullets, more than half of the residue was excreted in egg yolks within a months time. Hexachlorobenzene is slightly toxic to fish, which bioaccumulates rapidly in aquatic organism. Fish are the most sensitive organisms to the dioxin contaminants in penta--concentrations in parts per quadrillion (pg/l) to parts per trillion (ng/l) TCDD are acutely toxic to freshwater fish. Significant adverse effects are present at levels of 0.6 pg/l TCDD.54 The hepta- and hexachlorodibenzo-p-dioxins found in penta are considered to be 0.01 to 0.1 times as toxic as TCDD.55 Available data also indicate that the dioxins are extremely toxic to both birds and mammals. 

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