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2C - Biomarkers (TUP/106) Dose dependant inhibition of esterase activity in Helisoma duryi and Lymnaea natalensis. Naik, Yogeshkumar1, Basopo, Norah2, Nyathi, Clever3, 1 Department of Environmental Science & Health, NUST.PO Box AC 939, Bulawayo, Matabeleleland, Zimbabwe2 Department of Applied Biology & Biochemistry, NUST., Bulawayo., Matabeleleland, Zimbabwe3 Department of Applied Biology & Biochemistry, NUST., Bulawayo., Matabeleleland, Zimbabwe ABSTRACT- The effect of pesticide exposure in vivo on esterase activity of two aquatic snails Lymnaea natalensis and Helisoma duryi was studied. We have prevsiously shown that exposure, of both species, to 25 ppb of selected pesticides caused inhibition of esterase activity with the order of potency; monocrotophos > pirimiphos methyl >dimethoate >carbaryl. Here we report on the inhibition of esterase activity to lower doses of pesticides in order to identify the lowest concentration of pesticide capable of causing a detectable effect. Adult snails, reared in outdoor cement aquaria, were exposed to different concentrations (0.1 ppb, 0.5 ppb, 1 ppb, 5 ppb or 10 ppb) of pesticide (pirimiphos methyl, monocrotophos, dimethoate or carbaryl) for 3 days. Food and pesticide were replaced daily. Post-mitochondrial supernatants, of whole snail homogenates were used to measure esterase activity. Cholinesterase activity was measured using either acetylthiocholine iodide or S-butrylthiocholine iodide. Non-choline esterase activity was measured using either phenyl acetate, 4-nitrophenyl acetate or Key words: carbamates, organophosphates, esterases, aquatic snails |
-naphthyl acetate as substrate. In both species, H.duryi and L.natalensis, inhibition occurred generally in a dose dependant manner. Inhibition of up to 50% was observed after exposure to as little as 1 ppb. Lower degrees of inhibition were observed at 0.5 ppb and 0.1 ppb although monocrotophos caused up to 75 % inhibition of non-cholinesterase activity after exposure to 0.1 ppb. The degree of inhibition, however, varied depending on species of snail and the pesticide used. Our data confirms that organophosphates are more potent inhibitors of esterase activity than carbamates and that all four pesticides inhibit both choline and non-cholinesterase activity in both species of aquatic snails. At the lower doses of exposure the potency observed, in general, was monocrotophos > pirimiphos methyl >dimethoate >carbaryl.