Pentachlorophenol (PCP), commonly known as penta, has been
used as a fungicide, molluscicide, insecticide, and wood preservative. Its use is
now permitted only for industrial purposes; agricultural and domestic uses are
prohibited, because it is classified as a highly hazardous pesticide.
The oral LD50 of penta in rats is
150–210 mg/kg body wt. Common signs of poisoning include nervousness, rapid pulse
and respiratory rate, weakness, fever, muscle tremors, convulsions, loss in righting
reflexes, and asphyxial spasms followed by death. Corneal injury may result from
splashes or vapor overexposure. Chronic poisoning results in emaciation, fatty
liver, nephrosis, and weight loss.
The persistence of penta in soil and water and apparent
widespread use has resulted in significant exposure to animals. Young swine have
died after dermal exposure to freshly penta-treated wood used in farrowing crates or
farrowing houses. In vivo studies in swine demonstrated that exposure to
penta-contaminated soil can result in significant dermal absorption of the
pesticide. Penta can be absorbed through intact skin and lungs and is an intense
irritant to the skin and mucous membranes. Penta absorption in skin was greater in
water or water-based mixtures than in 100% ethanol. Because animals typically have
access to water at all times, this hydrophilic characteristic of penta suggests
enhanced dermal absorption.
When absorbed, penta increases metabolism by uncoupling
cellular phosphorylation. Animals fed in troughs made of lumber treated with PCP may
salivate and have irritated oral mucosa. Both penta and its major metabolite,
tetrachlorohydroquinone (TCHQ), can induce epidermal hyperplasia in mice.
Poultry have been exposed to sawdust and shavings from
penta-treated wood. Associated adverse effects include reduced growth rates, kidney
hypertrophy, and decreased humoral immune response. Penta exposure can also result
in an off-taste to eggs and meat as a result of degradation of chlorophenols to
chloroanisols. Vaporization or leaching of penta in pens, enclosures, homes, and
barns has caused illness and death.
Cattle and pigs exposed to wood treated with commercial grade
penta had increased mortality, possibly decreased fertility in boars, and reduced
productivity (milk, meat, etc). The lethal dose in cattle and sheep is ~120–140
mg/kg body wt.
Commercial lots of technical-grade penta contain small but
biologically significant amounts of highly toxic impurities such as chlorinated
dioxins and dibenzofurans, tetrachlorophenols, and hydroxychlorodiphenyl ethers;
these compounds can exert their own effects such as early fetotoxicity.
Commercial-grade penta causes hepatic porphyria, increased microsomal monooxygenase
activity, and increased liver weight. Pure penta was not teratogenic in rats.
Penta can cause residues in animal tissues. Also, a
significant amount of hexachlorobenzene is metabolized in animal tissues to penta.
Pentachlorophenol is considered to be a carcinogen and a tumor promoter, although
studies have shown that the pure material does not increase the incidence of tumors
in rats and mice. The technical-grade material has also been shown to be immunotoxic
in laboratory studies. Penta must be handled very carefully and kept away from
Whole blood analysis for penta may aid in the diagnosis of
poisoning; diagnosis is usually made on the basis of the signs and the proximity of
treated lumber in the animal's environment.
There is no known antidote. Termination of exposure, bathing
dermally exposed animals, oral administration of activated charcoal, and supportive
therapy may be indicated. Bathing should be done gently with cold water and
detergent so as not to cause vasodilation and increased absorption. Antipyretics,
eg, aspirin and acetaminophen, should not be used. Treatment involves cooling the
animal and administering fluids, electrolytes, and anticonvulsants.
Last full review/revision May 2014 by P. K. Gupta, PhD, Post Doc (USA), PGDCA, MSc VM & AH BVSc, FNA VSc,
FASc, AW, FST, FAEB, FACVT (USA), Gold Medalist