Combined effects of technical grade fenitrothion, humic acids and particulate matter on cholinesterase activity in freshwater invertebrates

Abstract

Purpose: The relative sensitivity of two freshwater invertebrate organisms to the organophosphorus insecticide fenitrothion was assessed by measuring cholinesterase (ChE) activity, a wellknown biomarker of both exposure and effect to organophosphorus pesticides. The influence of different concentrations of humic acids (HAs) and particulate matter on fenitrothion bioavailability was assessed in the more sensitive species. Materials and methods: The selected invertebrates were the dwelling feeding oligochaete Lumbriculus variegatus and the pulmonate gastropod Biomphalaria glabrata. Acute 48- h bioassays were performed exposing organisms to different fenitrothion concentrations. The concentrations that induced 50 % inhibition of enzyme activity (EC50) were calculated. Fenitrothion bioavailability was investigated using different concentrations of commercial HA or particulate matter. Sand and a diverse selection of chromatographic resins that have been proposed as analogues of natural sediments were selected. For these experiments, animals were exposed to a fenitrothion value similar to the EC50. Results and discussion: The 48-h EC50 values were 12±2 and 23±3 μgl−1 for L. variegatus and B. glabrata, respectively. Depending on HA concentration and the characteristics of particles, ChE activity was similar or higher than the value recorded for animals exposed only to the pesticide in aqueous solution. Conclusion: The results indicated that L. variegatus was the more sensitive species of the two. In this species, fenitrothion bioavailability did not increase due to the presence of either different HA concentrations or particulate matter. The experimental approach may constitute a useful tool to predict the influence of dissolved organic matter and sediment particles on fenitrothion bioavailability and toxicity to nontarget aquatic invertebrates.