Influence of environmental changes on degradation of chiral pollutants in soils

Numerous anthropogenic chemicals of environmental concern-including some ph enoxy acid herbicides, organophosphorus insecticides, polychlorinated biphe nyls, phthalates, freon substitutes and some DDT derivatives-are chiral. Th eir potential biological effects, such as toxicity, mutagenicity, carcinoge nicity, and endocrine disrupter activity, are generally enantiomer-selectiv e, and different enantiomers are preferentially degraded (transformed) by m icro-organisms in various environments(1-8). Here we use field and laborato ry experiments to demonstrate that environmental changes in soils can alter these preferences, and to suggest that the preferences shift owing to diff erent groups of related microbial genotypes being activated by different en vironmental changes. In Brazilian soils, almost all pasture samples prefere ntially transformed the non-herbicidal enantiomer of dichlorprop ((RS)-2-(2 ,4-dichlorophenoxy)propionic acid), while most forest samples either transf ormed the herbicidal enantiomer more readily or as rapidly as the non-herbi cidal enantiomer. Organic nutrient enrichments shifted enantioselectivity f or methyl dichlorprop ((RS)-methyl 2-(2,4-dichlorophenoxy)propionic acid) s trongly towards preferentially removing the non-herbicidal enantiomer in so ils from Brazil and North America, potentially increasing phytotoxicity of its residues relative to that of the racemate. Assessments of the risks che mical pollutants pose to public health and the environment need to take int o account the chiral selectivity of microbial transformation processes and their alteration by environmental changes, especially for pesticides as up to 25 per cent are chiral(9).