| Summary: | Accelerated degradation (AD) is the increased breakdown of a pesticide (or homolog) upon its repeated application and has consequences for environmental contamination and pest control. However the depth of microbial analysis into the phenomenon has been limited. Atrazine was selected as a model pesticide as its microbial degradation pathway is well characterised, enabling the microbial capacity for the degradation of atrazine to be traced. Initially a lab study showed that two applications of atrazine, at agriculturally relevant concentrations, to soils naïve to s-triazines were sufficient to induce its rapid dissipation. The emergence of AD was affiliated with the detection of the atrazine degrading genes. Six other soils with various physio-chemical properties exhibited a similar pattern of AD with average DT50 values of 28.4 days after the first application of atrazine and 1.9 days after the second. The repertoire of atrazine degrading genes varied between the soils exhibiting AD, although the gene sequences were identical. All six soils that exhibited AD contained at least one atrazine degrading gene. Upon neutralisation of a soil that did not exhibit AD, AD was restored and the atrazine degrading genes became detectable. In addition there was shown to be an effect of soil pH on the sorption of atrazine. To extend the relevance of this study beyond AD the effects of standard methodologies applied in chemical risk assessments on bacterial communities were examined and shown to reduce diversity and cause a shift in community structure. In addition the effect of rarefaction on interpreting microbial community analyses was examined. Overall the AD of atrazine was shown to be affiliated with detection of the atrazine degrading genes which may have been carried by the small portion of taxa associated with atrazine treatment. Therefore future work would focus on functional analyses to link atrazine degradation to specific taxa. In addition OECD guidelines need to consider the effects of the conditions imposed on the microbial community, while rarefaction is recommended for microbial ecology studies in line with other investigations.
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