Acute expousure of the freshwater snail Planorbarius corneus to an environmental concentration os chlorpyrifos: Recovery studies of enzime activities in gonads and affects on reproduction

Abstract

Chlorpyrifos is an organophosphate insecticide widely used in a variety of food crops in Argentina and other countries. In a previous work we have reported that subchronic exposure to an environmental concentration of chlorpyrifos caused severe effects on reproduction of the freshwater hermaphrodite gastropod Planorbarius corneus. The aim of the present work was to study the effects of chlorpyrifos on the reproduction of this adult snail after an acute (2 days) exposure. Also B-esterase activities (cholinesterases and carboxylesterases) were measured in the gonads to study the possible link of the biochemical responses to the reproduction effects. Snails were exposed during 2 days to 5 µg L -1 of chlorpyrifos. Control and solvent control (acetone) groups were included in the bioassays. After the 2 days of exposure, some snails per group were used to measured enzyme activities and the other snails were transferred to water. Then, the bioassay was continued for 14 days. Snails were fed once a week. During the 14 days in water, the number of egg masses was registered and for each egg mass, the number of egg masses without eggs, the number of eggs per mass, the time for hatching, the hatchings and the survival of the offspring were counted. After the 2 days of exposure and after 14 days in water, snailswere placed on ice, the shells were removed and gonad homogenates were realized. Supernatant fraction (8 for each time and for each group) was used to measure cholinesterase and carboxylesterase activities and protein content. After an acute exposure 5 µg L -1 of chlorpyrifos caused a decrease on cholinesterase activity using acetylthiocholine as substrate (50 %) and carboxylesterase activities (26 % using p-nitrophenylacetate as substrate and 40 % using p-nitrophenylbutyrate) in gonads. After 14 days in water, no recovery ofcholinesterase activity was observed. However carboxylesterases measured with both substrates returned to control values. Regarding to reproduction effects, only an increase in the number of egg masses without eggs was observed. Recovery of carboxylesterases in gonads could be related to the lower effects observed onreproduction in compare with the subchronic exposure. After 14 days of exposure, 5 µg L-1 of chlorpyrifos has produced a strongly decrease in B-esterase activities and severe effects on reproduction as the decreases in the % of hatching and survival of the offspring ant the increases in egg masses without eggs and in the time of hatching. Exposures to environmental concentrations of chlorpyrifos caused different toxic effects on the reproduction of Planorbarius corneus depending on the time of exposure.