Chemical structure: C6Cl5OH

A close chemical relative of the widely-publicized and much-feared polychlorinated biphenyls (PCBs), pentachlorophenol (or PCP as it is usually abbreviated; it has no relation to the contraband dissociative drug also abbreviated PCP) is a halogenated hydrocarbon, composed of a benzene ring to which is attached a hydroxide radical making a phenol which is then chlorinated. PCP is also associated with (and often contaminated by) tetrachlorophenol, hexachlorobenzene and various dioxins. Dioxins are among the most carcinogenic chemicals in the world, and hexachlorobenzodioxin appeared in commercially produced pentachlorophenol during the 1970s in amounts ranging up to 100 parts per million, a profoundly dangerous concentration according to the World Health Organization.

Pentachlorophenol has historically been used much like coal tar creosote in that it is used as a preservative and antibacterial agent for power line poles, railroad ties, cross arms and fence posts. It was once one of the most commonly used insecticides and herbicides, but now its use for such purposes is almost forbidden. Only certified applicators may now use PCP as a wood preservative.

PCP generally appears as a colorless crystal in its pure form, or as dark gray to gray-brown dust, beads or flakes in its impure form. It has a very strong chemical smell when hot, but is almost odorless at room temperature. PCP is not easily dissolved in water, and does not tend to evaporate, causing it to remain in a solid or viscous liquid state. Sunlight and microorganisms in surface water can break PCP down, so greater concentrations of PCP are found the deeper one goes, with the highest concentrations on the sea bottom. Of course, the chemicals into which PCP is broken down have their own set of dangers. PCP, though, is still the overriding concern.

PCP is bioaccumulative, and when introduced into marine environments can kill local marine life, including the bacterial mats on which sessile organisms base themselves, as well as larger plankton, fish, shellfish and crabs. In lower quantities, PCP concentrations can build up in marine organisms to levels which are extremely dangerous to humans. PCP is also accumulative in humans; much of it is excreted in urine, but quantities build up in muscle, bone marrow and fat. Exposure to such quantities of PCP can damage the liver, kidneys, blood, lungs, nervous system, immune system and gastrointestinal tract. It is likely, based on studies performed on animals, that PCP is carcinogenic to humans. Its accompanying contaminants and impurities, such as hexachlorobenzodioxin, are proven (and very dangerous) carcinogens. Studies performed in places where PCP is used indicate a clear link between PCP and leukemia, as well as several other cancers.

An additional danger of PCP is the fact that the difference between a lethal and non-lethal dose is very small. In studies performed on rabbits, a dose of 80mg per kilogram of body weight had no effect, whereas a 100mg per kilogram dose was lethal to 83% of the animals used in the study.

Sources: Agency for Toxic Substances and Disease Registry (, Consumer Law Page (, Environmental Protection Agency (, various World Health Organization reports.

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