BENZO[A]PYRENE HYDROXYLASE AND GLUTATHIONE-S-TRANSFERASE ACTIVITIES AS BIOMARKERS IN LYMNAEA-PALUSTRIS (MOLLUSCA, GASTROPODA) EXPOSED TO ATRAZINE AND HEXACHLOROBENZENE IN FRESH-WATER MESOCOSMS

Freshwater pond mesocosms were used to validate xenobiotic-metabolizin g enzymes as biomarkers of contamination by atrazine and hexachloroben zene (HCB) in a basommatophoran gastropod, Lymnaea palustris (Muller). Over long-term (21-d) exposure to 5, 25, and 125 mu g/L atrazine and to 0.5, 1.25, and 5 mu g/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 a trazine was faster than that of HCB. Although it affected the integrit y of microsomal membranes, HCB had no relevant effects on BaPH and GST activities at concentrations which affected growth and fecundity, thu s confirming the low inducibility of mollusc xenobiotic-metabolizing e nzymes by chlorinated compounds. In contrast, atrazine markedly inhibi ted BaPH and both postmitochondrial and cytosolic GSTs at the same con centrations, which had no effects on growth or reproduction. Enzyme in hibition 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 betwee n the bioconcentration factor and enzyme inhibition may serve as a des criptor of the physiological status of animals and can also be used to indirectly estimate the pesticide concentration in the environment. L aboratory data were considered for the interpretation of results obtai ned in the mesocosms. In the biomarker context, BaPH and GST activitie s are proposed, along with other biochemical markers already identifie d in atrazine- and HCB-exposed L. palustris, as elements of a multipar ametric approach of the ecotoxicological effects of pesticides on fres hwater ecosystems.