Chirality of pollutants?effects on metabolism and fate

Abstract

In most cases, enantiomers of chiral compounds behave differently in biochemical processes. Therefore, the effects and the environmental fate of the enantiomers of chiral pollutants need to be investigated separately. In this review, the different fates of the enantiomers of chiral phenoxyalkanoic acid herbicides, acetamides, organochlorines, and linear alkylbenzenesulfonates are discussed. The focus lies on biological degradation, which may be enantioselective, in contrast to non-biotic conversions. The data show that it is difficult to predict which enantiomer may be enriched and that accumulation of an enantiomer is dependent on the environmental system, the species, and the organ. Racemization and enantiomerization processes occur and make interpretation of the data even more complex. Enantioselective degradation implies that the enzymes involved in the conversion of such compounds are able to differentiate between the enantiomers. "Enzyme pairs" have evolved which exhibit almost identical overall folding. Only subtle differences in their active site determine their enantioselectivities. At the other extreme, there are examples of non-homologous "enzyme pairs" that have developed through convergent evolution to enantioselectively turn over the enantiomers of a chiral compound. For a better understanding of enantioselective reactions, more detailed studies of enzymes involved in enantioselective degradation need to be performed.

The international polar year (IPY) circumpolar flaw lead (CFL) system study: The importance of brine processes for α‐ and γ‐hexachlorocyclohexane (HCH) accumulation or rejection in sea ice

“…Although these enantiomers exhibit identical basic physical and chemical properties they behave differently when degraded by microbes because enzymes exhibit stereoselectivity (Müller and Kohler, 2004). Accordingly, the racemic (1:1) mixture of α-HCH released into the environment undergoes enantioenrichment when enantioselective processes are considered (microbial breakdown, selective biological uptake, biotransformation and elimination pathways in food webs (Faller et al, 1991;Falconer et al, 1995;Wiberg et al, 2000)).…”

Enantiomer Fractions of Organic Chlorinated Pesticides in Arctic Marine Ice Fauna, Zooplankton, and Benthos

“…In addition to area-specific exposure to nonracemic chiral chemicals in water, biota may alter the enantiomeric proportions by selective uptake, biotransformation, and elimination (5,9,(13)(14)(15). In the Canadian and Alaskan Arctic, marine zooplankton had (+)-R-HCH depletions similar to those of the water, suggesting no or limited biotransformation in these organisms (9,10).…”

Levels and Chiral Signatures of Organochlorine Pesticides in Urban Soils of Yinchuan, China

“…Some organochlorine pesticides are chiral, such as trans-chlordane (TC), cischlordane (CC), heptachlor, a-HCH and o,p 0 -DDT, and they were usually used by racemic mixture. To our knowledge, most of previous investigations commonly focused on the total residual levels, as a result, current knowledge of them was often inaccurate due to the different toxicological properties and rates of metabolism of chiral pesticides in the environment (Muller and Kohler 2004;Wiberg et al 2001). Therefore, study on chiral signatures of pollutants will be helpful to further understand the toxicological mechanism and environmental behavior.…”