Benzo[a]pyrene hydroxylase and glutathione s‐transferase activities as biomarkers in Lymnaea palustris (mollusca, gastropoda) exposed to atrazine and hexachlorobenzene in freshwater mesocosms

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Abstract
Freshwater pond mesocosms were used to validate xenobiotic‐metabolizing enzymes as biomarkers of contamination by atrazine and hexachlorobenzene (HCB) in a basommatophoran gastropod, Lymnaea palustris (Müller). Over long‐term (21‐d) exposure to 5, 25, and 125 μg/L atrazine and to 0.5, 1.25, and 5 μg/L HCB, the uptake and internal concentration of both pesticides were followed, and the activities of benzo[a]pyrene hydroxylase (BaPH) and glutathione S‐transferases (GSTs) of pesticide‐exposed snails were compared with those of control animals maintained in untreated mesocosms. Internally recovered HCB concentrations were much higher than internal atrazine concentrations, but the uptake of atrazine was faster than that of HCB. Although it affected the integrity of microsomal membranes, HCB had no relevant effects on BaPH and GST activities at concentrations which affected growth and fecundity, thus confirming the low inducibility of mollusc xenobiotic‐metabolizing enzymes by chlorinated compounds. In contrast, atrazine markedly inhibited BaPH and both postmitochondrial and cytosolic GSTs at the same concentrations, which had no effects on growth or reproduction. Enzyme inhibition was negatively correlated with the maximal internal amount of atrazine and positively correlated with the bioconcentration factor, suggesting that effects on xenobiotic‐metabolizing enzymes may affect pharmacokinetics of atrazine within the snail body. Correlation between the bioconcentration factor and enzyme inhibition may serve as a descriptor of the physiological status of animals and can also be used to indirectly estimate the pesticide concentration in the environment. Laboratory data were considered for the interpretation of results obtained in the mesocosms. In the biomarker context, BaPH and GST activities are proposed, along with other biochemical markers already identified in atrazine‐ and HCB‐exposed L. palustris, as elements of a multiparametric approach of the ecotoxicological effects of pesticides on freshwater ecosystems.

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