Azinphos-Methyl vs Carbaryl: Effects on B-Esterases of a Freshwater Snail

PÉREZ, ANALÍA FERNANDA; HERBERT, LUCILA THOMSETT; KRISTOFF, GISELA; COSSI, PAULA FANNY

San Pablo, Santos

Congreso; SETAC Latin America 12th Biennial Meeting; 2017

Organophosphate and carbamate compounds are widely used in agriculture for pest management control. The main mechanism of action of these kinds of insecticides consists in the inhibition of the enzyme acetylcholinesterase. In Argentina, Loewy et al. (1999, 2011), through surface and ground water monitoring detected a maximum concentration of the organophosphate azinphos-methyl (AZM) of 79.3 µg L-1 and of the carbamate carbaryl (CAR) of 45.7 µg L-1.We aimed to compare the effect of AZM and CAR on the activity of cholinesterases (ChEs) and carboxylesterases (CEs) of Biomphalaria straminea, a freshwater gastropod native to Argentina. Two bioassays were conducted in which four treatments were designed for each: dechlorinated tap water, acetone in dechlorinated tap water (solvent control), and AZM/CAR in dechlorinated tap water at 20/12.68 and 200/126.8 µg L-1, respectively. The concentrations of CAR were chosen so as to have the same molarity as AZM. Also, a fifth treatment was added for CAR, the equivalent to 126.8 µg L-1 of a formulation with 85 % of the active compound. As AZM has been prohibited (resolution 149/2016) we couldn?t get a formulation. Eight glass vessels were used per treatment with 200 mL of the corresponding solution. Based on previous stability studies, AZM and CAR solutions were renewed every 96 and 48 h, respectively. After 14 days of exposure homogenates were made with the organisms? soft tissues. In the supernatant fraction, the activity of ChEs and CEs, using as substrates p-nitrophenyl acetate (p-NPA) and p-nitrophenyl butyrate (p-NPB), were measured.The activity of ChEs was significantly inhibited (22 %) with 200 µg L-1 of AZM with respect to the water control. Regarding CEs, the highest concentration of AZM also significantly inhibited the enzyme by 24 % with p-NPA and 44 % with p-NPB, in relation to the water control. Instead, CAR did not elicit an effect on the activity of ChEs and CEs.Our results show that CE activity, measured with p-NPB, could be considered a sensitive biomarker in B. straminea after a subchronic exposure to AZM. Neither of the biomarkers evaluated in this study resulted sensitive after a subchronic exposure to CAR. The formulation of CAR did not show to be more toxic than the active compound itself.