Human impacts on soil community mineralization of chloroaromatics

Many organic pollutants such as pesticides are chlorinated organics, and until recently these were thought to be purely the product of anthropogenic activities. However, some chlorinated phenolics are now known to be part of the natural chemical make up of “pristine” soils, defined as those that have not previously been directly exposed to anthropogenic inputs, except through atmospheric contamination. The ability of a wide variety of these soils to mineralize a range of chlorinated aromatic chemicals has been investigated, and contrasted to the mineralization potential of agricultural soils. Our work has shown that in some instances pristine forest soils have a greater ability to degrade some chlorophenolics than agricultural soils, and that the latter harbour more specialized degradative communities. In addition to what appears to be a more generalist degradative community, pristine soils harbour high diversities of the genes encoding isofunctional enzymes important in the degradation of chloro-aromatics. In addition, these genes are often found in hosts that are quite different from those that carry them in more contaminated sites, suggesting that adaptation of soils to higher concentrations and more constant levels of chloro-organic inputs involves the loss of detectable genetic diversity.