Pentachlorophenol: Toxicology and Environmental Fate by Brett Fisher However, Is Incomplete
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Pentachlorophenol: Toxicology and Environmental Fate By Brett Fisher however, is incomplete. Technical grade etrated the skin than had been estimated penta contains from 4 to 12 percent by EPA: 62 percent of the penta in oil Pentachlorophenol (penta or PCP) tetrachlorophenols, which are toxic in was absorbed and 16 percent of the was first introduced for use as a wood their own right. In addition, the high penta in water.13 Two recent studies of preservative in 1936 by Dow Chemical temperatures used in manufacturing sawmill workers exposed to water- Company and Monsanto Chemical Com- penta produce several contaminants in- based penta support these find- pany.1 Penta has since been used as an cluding hexachlorobenzene, dioxins, and ings.10,14 These findings suggest that herbicide on ornamental lawns, golf furans (see Figure 1).2 workers and others, such as those liv- courses, aquatic areas, and rights-of-way; There are two general methods for ing in treated homes or children who for control of subterranean termites; as preserving wood, the pressure process play on treated playground structures, an anti-microbial agent in cooling tow- and the non-pressure process. The pres- may be at greater risk from exposure ers, adhesives, latex paints, paper coat- sure-treating process involves placing through skin contact than estimated ings, cements used with food can ends the wood in a pressure-treating vessel by EPA. and seals, coatings in reusable bulk where it is immersed in the preserva- Although most people are not occu- food storage containers, photographic tive and then subjected to applied pres- pationally exposed to penta, research- solutions, leather tanneries, and pulp sure. The excess penta is vacuumed ers for the national Health and Nutri- and paper mills; and, as a disinfectant.2 from the vessel and the treated wood is tional Examination Survey II of the Na- It is marketed under the trade names removed, inspected, stored, and tional Center for Health Statistics found Santophen, Penchlorol, Chlorophen, shipped. In the non-pressure process, Pentacon, Penwar, Sinituho and Penta penta is applied to the surface of wood Figure 1 among others.3 by spraying, brushing, dipping, and soak- Pentachlorophenol and As of 1977, about 50 million pounds ing. This process is used for short-term Some of Its Contaminants of penta were produced annually in the wood protection in construction where Cl United States.2 In 1985, 35 million pounds the wood will be protected from expo- Cl Cl of penta were manufactured in the U.S.4 sure to soil or weather through brick or Vulcan Chemicals, located in Wichita, cement barriers. This process is also Cl Cl 5 Kansas, is penta’s sole U.S. producer. used to control sapstain fungi (fungi OH In 1988, the U.S. Environmental Protec- which leave a blue stain on wood) by Pentachlorophenol tion Agency (EPA) cancelled all uses of passing green lumber through a spray O penta except for its use as a wood pre- tunnel or by dipping the wood.7 Cl Cl servative.6 Cl Cl There are two manufacturing pro- Human Exposure cesses used to produce penta: (1) the People are exposed to penta in the Cl Cl direct chlorination of phenol, the workplace, in treated homes, indoor and O Boehringer process; and (2) the alkaline outdoor air, drinking water, and food. A hexachlorodibenzo-p-dioxin hydrolysis of hexachlorobenzene, the Penta can enter the body through inha- Dow process. In Europe, approximately lation, ingestion of contaminated food Cl Cl equal use is made of both methods. In or water, and skin contact with treated the US, penta is produced solely by the wood. Cl Cl 7 Boehringer process. Workers in wood preserving facilities, ClO Cl Chlorination of phenol in the sawmills and other workplaces who Boehringer process occurs in two stages. handle penta or treated wood receive A hexachlorodibenzofuran In stage one, chlorine is bubbled through the most significant exposures primarily Cl phenol at 105° F to yield tri- and through skin contact and secondarily Cl Cl tetrachlorophenols (phenols with three through air.6,7,8,9,10,11 Based on limited and four chlorine atoms respectively). data from animal studies, EPA has esti- Cl Cl In stage two, the temperature is gradu- mated that human skin absorbs 50 per- Cl ° ally increased to 130 F to keep the reac- cent of the amount of penta it is exposed Hexachlorobenzene tion mixture molten and to further chlo- to from oil-based formulations and 1 per- rinate the tri- and tetrachlorophenols to cent from water-based formulations.12 Cl form pentachlorophenol. The process, Researchers from the University of Cl Cl Washington, however, who applied amounts of penta to skin from human Cl Brett Fisher coordinates NCAP’s infor- cadavers to simulate levels at which OH mation services and groundwater cam- people are exposed found more pen- A tetrachlorophenol paign. 2 JOURNAL OF PESTICIDE REFORM / VOL. 11, NO. 1 penta in 79 percent of urine samples a higher metabolic rate and therefore treated containers.16 from the general population.15 In a breathe more often relative to body In addition, use of penta treated study of 179 Arkansas children, 100 weight and blood volume than adults. wood that comes in contact with live- percent of the urine samples tested They also suggested that skin contact stock can contaminate animal prod- positive for penta with an average level with treated walls could raise blood ucts with penta or its contaminants.26 of 14 parts per billion (ppb).16 Penta levels of penta in very young chil- In a study of pork and chicken in is also present in human fat tissues dren.21 Canada, 60 percent of 144 samples and human breast milk.17,18 In fact, sur- contained penta while half of 26 veys of the literature on human expo- chicken fat samples with high levels sure to penta indicate that people liv- of penta also contained hexa-, hepta-, ing in industrialized societies will gen- or octa- dioxins (those with six, seven, erally be contaminated with penta at “In a 1976 spot survey and eight chlorine atoms per dioxin concentrations of 1 to 100 ppb.19 of selected foods, penta molecule).27 In a survey of cow milk in One source of exposure to penta in Ontario, Canada, 57 percent of 359 the general population is from indoor residues ranging from 1 samples contained penta at an aver- air and dust. Residents of log homes to 100 ppb were found age of 29 ppb. The exposure of dairy treated with penta in Kentucky were in powdered dry milk, cattle to penta was attributed to penta found to have elevated levels of penta contaminated wood shavings or saw- in their blood (580 - 1,750 ppb) and soft drinks, bread, dust used as litter; direct contact be- urine (47 - 216 ppb). The source of candy bars, cereal, tween the cows and treated wood; and the exposure was continuous vapor- contact between feed and treated ization of penta from factory-treated noodles, rice, sugar, wood.28 logs. The youngest children had the and wheat.” highest blood levels of penta, even Human Toxicology though they spent as much time in Acute Toxicity: The acute toxicity the home as older children and of penta is believed to derive from its adults.20 ability to interfere with the produc- Researchers measuring levels of Penta, and other toxins, accumulate tion of energy at the cellular level. This penta in humans reported an average in household dust and can contribute interference (uncoupling of oxidative 40 ppb in the blood of the general to the total exposure of children and phosphorylation) causes increased population and an average of 420 ppb adults. Because of their lower body cell metabolism resulting in increased in 143 residents of log homes in nine weight, greater dermal contact with heat production.3,7,19 states. The children residing in penta dust, and frequent hand-to-mouth ac- A person may have up to about 100 treated log homes were found to have tivity, young children ingest at least ppb of penta in their blood and urine 1.8 times more penta in their blood 2.5 times more dust than adults.22 In a before they begin to experience ad- than adults. Because the primary route study of German homes, penta has verse effects.1 Levels of penta found of exposure to penta in homes is been found in house dust at levels that in various organs and fluids after fatal through the air, the researchers con- remained relatively high over time poisonings range from 20 to 145 ppm cluded that children could be ex- while levels in indoor air decreased.23 in adults. Levels of penta in children pected to have more penta in their In a study of Seattle homes, penta was and infants after fatal poisonings are blood than adults because they have found in house dust at an average level lower, indicating children are more of 3.4 parts per million (ppm). In two susceptible to penta than adults. Sur- of these homes, the penta may have veys of poisonings reported in the lit- Figure 2 Predicted Average Daily been tracked in from decks that had erature suggest that the largest single Intake of Pentachlorophenol 25 been treated with penta three and five dosage that produces no illness is little years before the samples were col- less than the fatal dosage.29 .9 5.1 .09 24 .5 lected. The most common symptoms of Because an estimated 96.5 percent those experiencing penta poisoning in- of the penta in the environment will clude stuffy nose, scratchy throat, and end up in soil, researchers looking at tears in the eyes.