Toxicokinetic and toxicodynamic studies of carbaryl alone or in binary mixtures with azinphos methyl in the freshwater gastropod Planorbarius corneus
•Snails were exposed for 48 h in single-chemical and binary-mixture studies.•CB inhibited ChE activity in soft tissues and hemolymph with similar EC50 values.•Carboxylesterases were more sensitive than ChE to CB inhibition in both tissues.•ChE activity in mixtures of CB + AZM followed a concentratio...
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| Published in: | Aquatic toxicology Vol. 199; pp. 276 - 284 |
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| Main Authors: | , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Netherlands
Elsevier B.V
01-06-2018
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | •Snails were exposed for 48 h in single-chemical and binary-mixture studies.•CB inhibited ChE activity in soft tissues and hemolymph with similar EC50 values.•Carboxylesterases were more sensitive than ChE to CB inhibition in both tissues.•ChE activity in mixtures of CB + AZM followed a concentration addition model.•Mixtures did not change the toxicokinetic parameters of the parent compounds.
Carbamate insecticides such as carbaryl and organophosphates such as azinphos-methyl share the ability to inhibit the activity of B-esterases. This study aimed to (1) assess the inhibitory effects of carbaryl on B-esterase activity in soft tissues and hemolymph of Planorbarius corneus; (2) establish whether binary mixtures of carbaryl and azinphos-methyl depart or not from a model of concentration addition on the inhibition of cholinesterase activity; (3) determine the bioconcentration and elimination of the pesticides. The results showed that exposure of gastropods to increasing concentrations of carbaryl (0.1–5 mg L−1) for 48 h inhibited cholinesterase activity in a concentration-dependent manner, with an EC50 of 1.4 ± 0.3 mg L−1 and 1.2 ± 0.1 mg L−1 for soft tissue and hemolymph, respectively. Carboxylesterase activity, measured with the substrates p-nitrophenyl butyrate and p-nitrophenyl acetate, was between 2.3 and 25 times more sensitive to carbaryl inhibition than cholinesterase activity. Binary mixtures corresponding to 0.5 EC50 carbaryl + 0.5 EC50 azinphos-methyl and 0.75 EC50 carbaryl + 0.75 EC50 azinphos-methyl produced inhibitions of cholinesterase activity similar to those of individual pesticides, following a model of concentration addition. Bioconcentration was analyzed using a one-compartment model. The absorption kinetics (k1) for both pesticides alone (1.4 mg L−1 of carbaryl or 1.8 mg L−1 of azinphos-methyl) or mixed (1.4 mg L−1 of carbaryl + 1.8 mg L−1 of azinphos-methyl) were similar. The elimination kinetics ratio (k2) estimated for the pesticides alone or in the mixtures showed that carbaryl was eliminated 3.5 times faster than azinphos-methyl. These results suggest that exposure of Planorbarius corneus to binary mixtures of carbaryl and azinphos-methyl for 48 h follow a concentration addition model on inhibition of cholinesterase activity and that the pesticide mixtures do not change the toxicokinetic parameters of the parent compounds. |
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| ISSN: | 0166-445X 1879-1514 |
| DOI: | 10.1016/j.aquatox.2018.04.005 |