Pentachlorophenol (PCP) decomposing activity of field soils treated annually with PCP

Soil from field plots (Hokkaido Agricultural Experiment Station, Memuro, Japan) that had been treated once a year with pentachlorophenol (PCP) and from untreated plots was tested for PCP-decomposing activity in the laboratory. When PCP as an aqueous solution of pentachlorophenolate was added to both sets of soil samples, no significant difference was noticeable in the PCP-decomposing activity, despite a 1000-fold difference in the number of PCP-decomposing microorganisms. When PCP was added as a PCP-celite mixture, however, PCP-decomposing activity was related to the history of the plot's treatment. The activity of the soil from PCP field plots was consistently higher than that from non-treated plots. When PCP was added to the untreated soil and incubated, the number of PCP-decomposing microorganisms increased, reaching the same order as that of PCP-treated soil plots after 3–4 weeks.