Environmental fate of DDT isomers and metabolites

Abstract

It is known for decades that 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-trichlorethane, better known as p,p′-DDT, and its accompanied substitution isomer 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1,1-trichlorethane (o,p′-DDT). Therefore, for this literature review over 2000 recent literature citations were checked for information on the isomer ratios of DDT and its metabolites in the environment. 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. However, this review revealed evidence for remarkable changes and shifts in o,p′-/p,p′-ratios of DDX. The application of isomer specific analysis remains dominantly on emission source apportionment, e.g. to differentiate DDT and dicofol emission. Only very few studies linked observed isomer shifts to aspects of environmental processes, such as (i) volatility from soil to air, (ii) environmental stability in soil or (iii) bioaccumulation in fishes. Additionally, several studies failed to use isomer specific interpretation in order to obtain more detailed insight into environmental processes e.g. for observed isomer shifts during air-water fluxes. Evaluating the comprehensive data set presented in this review a clear discrimination of o,p′-/p,p′-ratios of DDT, DDD and DDE is evident. The o,p′-/p,p′-ratios of DDT and DDD have been detected more or less on the same level, whereas the isomers of DDE were definitely depleted by the o,p′-isomer in all environmental compartments. This observation indicates a general isomer-specific differentiation during DDT metabolism. Finally, the potential to follow the environmental fate of DDX via the isomer composition has not been realized accurately so far, and, consequently, has not been well established in the field of environmental chemistry yet.