Chilina gibbosa: sentinel species for water contamination?

BIANCO, KARINA; KRISTOFF, GISELA

LAMBERT Academic Publishing

Año: 2014 p. 69

978-3-659-64267-8

Due to the aquatic contamination produced by the use of pesticides in agriculture, some species are used to monitoring the water quality. The orgaphosphate azinphos-methyl and the carbamate carbaryl were the most frequent pesticides found in the Upper Valley of Río Negro y Río Neuquén region, in Argentina. The primary acute toxicity of these pesticides is related to the inhibition of the acetylcholinesterase enzyme. Cholinesterases and also carboxylesterases are used as biomarkers of exposure or/and effect to these pesticides. Chilina gibbosa is a freshwater gastropod naturally found in Argentina. A characterization of their B-esterases and the study of azinphos-methyl effect on their activity were performed. The characterization was performed using three substrates for cholinesterases: acetylthiocholine, propionylthiocholine and butyrylthiocholine, and two substrates for carboxylesterases: p-nitrophenyl acetate and p-nitrophenyl butyrate. Also, the kinetic parameters Vmáx and Km were estimated and the in vitro inhibition with eserine (cholinesterases inhibitor) and iso-OMPA (butyrylcholinesterases inhibitor) was evaluated. Then, the 48 hours exposure to different concentrations of azinphos-methyl was performed. Cholinesterases, carboxilesterases and proteins were measured in the supernatant of 11,000 xg of the total soft tissue of each snail. The 50% inhibition concentration (IC50) and the non observed effect concentration (NOEC) were estimated. Effects of environmental concentrations of azinphos-methyl on antioxidant defenses: glutathione, catalase, superoxide dismutase and glutathione S-transferase were also studied. The highest specific activity was obtained whith acetylthiocholine as substrate. Eserine produced a high inhibition of cholinesterases. Iso-OMPA did not cause inhibition of cholinesterases, coincidently with the low hydrolysis measured with butyrylthiocholine.Regarding carboxylesterases activities, Vmax was higher and apparent Km was lower with p-nitrophenyl butyrate. 48 hours exposure to environmental concentrations of azinphos-methyl caused a high inhibition of cholinesterase activity. On contrary, carboxylesterases were inhibited at high concentrations. Regarding antioxidant defenses, glutathione levels were significantly increased by 0.02 and 20 μ g L-1 of azinphos-methyl, catalase activity was increased 85 % only at 0.02 μ g L-1 and superoxide dismutase and glutathione S transferase did not show any significant response. No lethality was observed after the assays, but organisms exposed to 0.01 μ g L-1 azinphos-methyl or higher, showed 52severe neurotoxicity signs. C. gibbosa is an organism sensitive to acute exposure to azinphos-methyl at environmental concentrations reported in Argentina. C. gibbosacould be used as a biomarker organism for aquatic contamination byorganophosphate insecticides. However, recovery, chronic and field studies should first be performed. At azinphos-methyl concentrations recommended in Argentina for aquatic life protection (0.02 μ g L-1) C. gibbosa showed severe neurotoxic effects, a strong inhibition of cholinesterases and an important increase in glutathione levels, after two days of exposure. These results suggest that the concentrations recommended of azinphos-methyl should be revised.