Pentachlorophenol persistence

The trend from heavy metal and phenolic based biocides, e.g. mercury and pentachlorophenol types, to more environmentally acceptable but less persistent organic types, requires more attention to plant hygiene (Figure 6, Briggs, 1980). 

In soils, PCP persisted for 15 to more than 60 days, depending on soil conditions and application rate. At initial concentrations of 100 mg PCP/kg soil, the Tb 1/2 was 10 to 40 days at 30°C under flooded conditions. However, in aerobic soils there was virtually no degradation after 2 months (Kaufman 1978). In rice paddy soils, initial concentrations of 4 mg PCP/kg fell to 2 mg/kg in 7 days (Bevenue and Beckman 1967). Pentachlorophenol was still measurable after 12 months in warm, moist soils (Cote 1972 USEPA 1980). In estuarine sediments, degradation was most rapid under conditions of increased oxygen and a pH of 8.0 (DeLaune et al. 1983). 

The toxicity of commercial or technical grades of PCP significantly exceeds that of analytical or purified PCP. Some of this added toxicity is attributed to impurities such as dioxins, dibenzo-furans, chlorophenols, and hexachlorobenzene. Pentachlorophenol is rapidly accumulated and rapidly excreted, and has little tendency to persist in living organisms. It acts by uncoupling oxidative... 

Kalman, D.A. and S.W. Horstman. 1983. Persistence of tetrachlorophenol and pentachlorophenol in exposed woodworkers. Jour. Toxicol. Clin. Toxicol. 20 343-352. 

Seidler, J.J., M. Landau, F.E. Dierberg, and R.H. Pierce. 1986. Persistence of pentachlorophenol in a wastewater-estuarine agriculture system. Bull. Environ. Contam. Toxicol. 36 101-108. 

Many chlorophenols are harmful and persistent. It is possible that these may be produced microbiologically in nature in view of the finding that a fungal chloroperoxidase halogenates phenol to yield monochlorophenols and the latter to give dichlorophenols. The sequence continues with producing trichlorophe-nols, tetrachlorophenols, and even pentachlorophenol [208]. 

The Binational Toxics Strategy between the USA and Canada has identified 12 bioaccumulative substances (referred to as Level-1 substances) having significant persistency and toxicity to the Great Lakes system, with the goal of reducing the sources of these substances to achieve naturally occurring levels [23]. Six of the 12 Level-1 substances are OC pesticides aldrin/dieldrin, chlordane, DDT, HCB, mirex, and toxaphene. Several other OC pesticides, such as endrin, heptachlor/heptachlor epoxide, hexachloro-cyclohexanes, tetra- and penta-chlorobenzenes, and pentachlorophenol, have been identified as Level-2 substances. 

Chlorinated phenols are among the most important contaminants in the environment (aqueous systems and soils) due to their widespread use in industry and agriculture and for domestic purposes for over 50 years. It is well-known that chlorophenols are toxic at low levels. The more highly chlorinated phenols such as trichlorophenols and pentachlorophenol are also persistent. Five of the chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) have been classified as priority pollutants by the US Environmental Protection Agency (EPA). 

Gorski T, Konopka L, Brodzki M. 1984. Persistence of some polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans of pentachlorophenol in human adipose tissue. Rocz Panstw Zakl Hig 35 297-301. 

Davila et al. [68] reported the transformation of the pesticides bromoxynil, dichlorophen, and pentachlorophenol by the versatile peroxidase from B. adusta. For the three transformed pesticides by versatile peroxidase, an oxidative dehalo-genation was observed, a very important process since the halogenated pesticides are considered more persistent and toxic than the organophosphorus pesticides, because of the carbon-halogen bond. Enzymatic transformation of dichlorophen compound... 

For most of the PCDDs no information on human health effects is available except that during the production of pentachlorophenol workers have developed a skin disease, chloracne (13) and complaints such as neuralgic pain in the lower extremities, and symptoms such as persistent bronchitis, and eye irritation (14). The bronchitis seems to be more prevalent in workers exposed to technical pentachlorophenol than in those exposed to the other chlorinated phenols. 

Organochlorine pesticides include aldrin, chlordane, dichophane (DDT), dieldrin (also a metabolite of aldrin) endrin heptachlor, hexachlorobenzene (EICB), 1, 2, 3, 4, 5, 6-hexachlorocyclohexane (EICEI = benzenehexachloride, BE1C), and lindane (gamma - EICEI). These compounds were widely used but persist in the environment, and lindane, which has a relatively short half-life in vivo, is now the only member of this group still in common use. Pentachlorophenol is used as a contact herbicide. This compound is still widely used in wood preservatives and disinfectants. 

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