A comparison of the ability of forest and agricultural soils to mineralizechlorinated aromatic compounds

Soils were sampled from two agricultural fields, two relatively pristine fo rests, and one suburban forest in Ontario, Canada. The ability of these soi ls to mineralize 2,4-dichlorophenoxyacetate, 3-chlorobenzoate, 4-chlorophen ol, 2,4-dichlorophenol, pentachlorophenol, and atrazine was determined usin g C-14-labeled substrates. Direct preexposure was necessary before atrazine mineralization could be detected; however, it was not necessary for degrad ation of any of the other chemicals. 2,4-dichlorophenoxyacetate and pentach lorophenol mineralization was much higher in the agricultural soils relativ e to the pristine forest soils, but 3-chlorobenzoate and 2,4-dichlorophenol mineralization rates showed the opposite trend. Mineralization of 4-chloro phenol was about equivalent in all soils. Suburban forests soils were indis tinguishable from agricultural soils with respect to their degradation of 2 ,4-dichlorophenoxyacetate and chlorobenzoate. Additionally, they were bette r able than any of the soils to withstand the toxic effects of pentachlorop henol. Pentachlorophenol mineralization was highly variable in the pristine forest soils, ranging from about 6 to 50%. Abiotic factors such as pH, soi l type, and organic and moisture content did not account for these signific ant site differences. The selective forces responsible for these difference s, and the possible differences in microbial populations are discussed.