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10.Effect of Pesticide-Degrading Processes on Soil Microflora and the Pesticide Degradation

Kyo Sato(Institute of Genetic Ecology,Tohoku University)

Changes in the population of the bacteria tolerant to the pesti- cide, PCP(pentachlorophenol) and some dechlorinated compounds of PCP were followed upon application of PCP and the compounds to so- il. Fifty ppm of 2,3,4,5-tetrachlorophenol and 2,4,5-trichlorophe- nol depressed an increase in the total viable number of bacteria, while PCP and 2,4,6-trichlorophenol did not cause a depression. When the compouds tested were not applied,no bacterial cells tole- rant to the compounds were established except for a slight proli- feration of the cells tolerant to 2,4,6-trichlorophenol.PCP estab- lished the cells tolerant to both PCP and 2,4,6-trichlorophenol, but did not establish those tolerant to 2,3,4,5-tetrachlorophenol and 2,4,5-trichlorophenol. 2,4,6-trichlorophenol also established cells tolerant to both PCP and 2,4,6-trichlorophenol. On the other hand, 2,3,4,5-tetrachlorophenol and 2,4,5-trichlorophenol establi- shed no cells tolerant to every compound. When different concent- rations of 2,3,4,5-tetrachlorophenol were applied, the cells tole- rant to the compound proliferated upon application of low concent- ration of the compound although proliferation of those tolerant to 50 ppm was scarce. However, in the case of 2,4,5-trichlorophenol this compound did not proliferate the cells tolerant to 50 ppm of the compound at all. The tolerance was also investigated for the bacteria isolated from the soils applied with the compounds. The results coincided with the pattern of establishment of the cells tolerant to the respective compounds in soil. From the above re- sults it is deduced that the effect of dechlorinated compounds on soil microflora differs depending on the kind of compounds. Of the compounds tested,2,4,5-trichlorophenol is most injurious to micro- bial proliferation in soil,2,3,4,5-tetrachlorophenol was less har- mful, whilst 2,4,6-trichlorophenol was least harmful.

Keywords: Pesticide, Pentachlorophenol, Pesticide-degradation, Soil microorganism, Soil microflora,