Applications of Carboxylesterase Activity in Environmental Monitoring and Toxicity Identification Evaluations (TIEs)

* Final gross prices may vary according to local VAT.

Get Access

The purpose of this review is to examine uses of carboxylesterase activity in environmental monitoring with a specific emphasis on pyrethroid insecticides. The chapter begins with an overview of the enzyme class, including general structure, function, catalytic mechanism, and substrate specificity. This section serves to introduce carboxylesterases, their biological significance, and their role in metabolism and detoxification reactions. Following this section, an in-depth analysis of different reports of applications of carboxylesterase activity in environmental monitoring is presented on an organism-specific basis. From an environmental standpoint, one of the most important carboxylesterase-mediated reactions is the hydrolysis and subsequent detoxification of pyrethroid insecticides. This reaction is one of the main detoxification pathways for pyrethroids in numerous organisms ranging from worms to fish to humans and is also an important pathway for the development of insect resistance to pyrethroid-associated toxicity. Accordingly, this class of insecticide is reviewed in more detail, with emphasis on toxicity and physical properties. The high hydrophobicity of pyrethroids is specifically addressed with a discussion of the effects of surface adsorption upon the observed toxicity in aquatic testing systems. A particular point is that changing agricultural practices combined with new legislation are causing a shift in insecticide usage patterns from organophosphates (OPs) and carbamates to pyrethroids. The effects of this shift are complex and potentially far reaching, especially the environmental consequences. In particular, the extreme toxicity of pyrethroids to many aquatic organisms, combined with their hydrophobicity, has resulted in concern regarding their potential environmental effects. This concern is exacerbated by the fact that current Toxicity Identification Evaluation (TIE) protocols devised for the identification of insecticides (and other environmental contaminants) in aqueous and sediment samples do not identify pyrethroid-associated toxicity with complete certainty. To address this shortfall, the use of carboxylesterase activity to hydrolyze pyrethroids in aquatic toxicity testing has been proposed as a simple, mechanistically based method to selectively identify pyrethroidassociated toxicity. This chapter reviews TIE protocols and the role of carboxylesterase activity in the development of TIE methods. A series of case studies are presented in which carboxylesterase activity was employed to identify pyrethroid-associated toxicity. Additional methods for the selective detection of pyrethroid-associated toxicity are also examined, including the use of temperature differentials and piperonyl butoxide (PBO). The strengths and weaknesses of the carboxylesterase-addition technique are also analyzed, with a number of distinct recommendations made for future development. Taken together, this review provides a detailed analysis of multiple applications of carboxylesterase to environmental monitoring and strongly advocates for further work on this enzyme system.