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  • Title: Toxicokinetic and toxicodynamic studies of carbaryl alone or in binary mixtures with azinphos methyl in the freshwater gastropod Planorbarius corneus.
    Author: Cacciatore LC, Verrengia Guerrero NR, Cochón AC.
    Journal: Aquat Toxicol; 2018 Jun; 199():276-284. PubMed ID: 29689476.
    Abstract:
    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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