Esterases of Corbicula fluminea as Biomarkers of Exposure to Organophosphorus Pesticides

BASACK SILVANA B.; ; ONETO, MARÍA L.; FUCHS JULIO S.; WOOD EDGARDO J.; KESTEN EVA M.

BULLETIN OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY

SPRINGER

Lugar: Berlin; Año: 1998

0007-4861

Organophosphorus pesticides (OPs), well known anticholinesterase agents, are inherently toxic substances that may pose risks to non-target organisms. Their interaction with some esterases led to the classification of these enzymes into three categories: A-esterases, that are able to hydrolyze OPs and are not inhibited by them; B-esterases ?cholinesterases (ChEs) and carboxylesterases (CaEs)?, that are typically inhibited by OPs; and C-esterases, that do not interact with this family of pesticides .The inhibition of the activity of ChEs ?acetylcholinesterase (AChE, E.C 3.1.1.7) and butyrylcholinesterase (BuChE, E.C 3.1.1.8)? has been frequently used as a biomarker to assess the extent of exposure to OPs, principally in vertebrate species (Walker and Thompson 1991). Bivalve mollusks are often considered as adequate organisms for ecotoxicological monitoring due to their capacity to filter large volumes of water, accumulate a wide range of contaminants, and reflect changes in the pollution status of their environment (Sheehan et al. 1995; Basack et al. 1997). However, until recently there have been few published studies on the use of ChE measurements as exposure biomarkers on aquatic invertebrates, and the activities assessed have been very low (Bocquené et al. 1990; Day and Scott 1990; Escartín and Porte 1997). Evidence shows that ChEs are polimorphic enzymes, which may be soluble or bound to membranes depending on species and tissue. These enzymes have been often studied only in the supernatant fraction obtained from homogenates centrifuged in the range of 10,000?18,000 x g (Day and Scott 1990; Escartín and Porte 1997). However, according to Fairbrother et al. (1991), it is essential to characterize ChE activities before using only the supernatant for enzyme activity determination.CaEs of bivalve organisms have shown higher sensitivity to OPs than AChE, and so they have been considered good candidates to be employed as biomarkers (Escartín and Porte 1997). Organisms have many esterases, and these enzymes -present in all tissues usually in the cytosol or in the microsomes? show clear evidences of some phylogenetic differences amongst species. Although several CaEs have been found in the mussel Mytilus galloprovincialis, there is scarce information on how many esterases may be present in other bivalves . Bivalves of the genus Corbicula have been used as biological monitors in freshwater environments and, according to our previous work, may be useful to assess the presence of organic compounds in water, including the less persistent chemicals . In order to evaluate the usefulness of the esterases of Corbicula fluminea taken from the Río de la Plata as potential biomarkers of OPs, this study had three different objectives. The first was to determine ChE activities both in the supernatant (ChE-S) and pellet (ChE-P) of whole soft tissue homogenates centrifuged at 10,000 x g, and the activity of CaE in the supernatant fraction. The second was to characterize ChE-S and ChE-P employing in vitro assays. The third objective was to assess the inhibition of CaE, ChE-S and ChE-P activities in vivo, by exposing the bivalves to different concentrations of the OPs parathion, paraoxon and fenitrothion.