DDT isomers and metabolites in the environment: an overview

It is known for decades that the isomeric composition of organic pollutants can be influenced substantially by environmental processes such as biotransformation or transfer between compartments. This accounts also for the pesticide 2,2,-bis(4-chlorophenyl)-1,1,1-trichloroethane, better known as p,p′-DDT, and its accompanied substitution isomer 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1,1-trichloroethane (o,p′-DDT). Although many studies followed the environmental fate of DDT, only very few publications reported on quantitative data of both o,p′- and p,p′-isomers. Therefore this condensed review describes evidence for remarkable changes and shifts in o,p′-/p,p′-ratios of DDT-related compounds. The application of isomer-specific analysis remains dominantly on emission source apportionment, for example, to differentiate DDT and dicofol emission. Only very few studies linked observed isomer shifts to aspects of environmental processes, such as (1) volatility from soil to air, (2) environmental stability in soil or (3) bioaccumulation in fishes. Additionally, several studies failed to use isomer-specific interpretation in order to obtain more detailed insight into environmental processes, for example, for observed isomer shifts during air–water fluxes. The o,p′-/p,p′-ratios of DDT and its main metabolite DDD have been detected more or less on the same level, whereas the isomers of the second main metabolite DDE were definitely depleted by the o,p′-isomer in all environmental compartments, indicating a general isomer-specific differentiation during DDT metabolism.