Toxicological evaluation of the marine sediments of the Huaylá estero in Ecuador, using the C. elegans nematode as bioindicator

Abstract

The Estero Huaylá, located in the Province of El Oro (Ecuador) has been impacted by the different human activities, such as agricultural industry, shrimp farms, larval breeding laboratories, sewage, and domestic effluent without treatment which are discharged directly into the waters of the estuary, contaminating it and neglecting all existing biological diversity. In this work, we evaluated the presence of metals in the marine sediments and their toxicity using the model organism Caenorhabditis elegans. Sediment samples from nine locations were dried and analyzed to determine the presence of mercury and lead by atomic absorption spectrophotometry with flame fogging and the generation of hydrides with atomization in a quartz cell. In assess the toxicity, C. elegans was exposed to aqueous extracts of sediments and changes in biological parameters such as survival, locomotion, growth and reproduction, and biochemical parameters such as changes in the expression of genes for stress response by metals and oxidative stress through the expression of mtl-2::gfp and sod-4::gfp, respectively. The results show that the mercury concentration was high at all points, and the lead concentration was low. The wild C. elegans exposed to the extracts of sediments showed effects on mortality, growth, locomotion and reproduction. The transgenic nematodes presented overexpression of the mtl-2 and sod-4 genes. In general, the points with the highest concentration of mercury and greater toxicity were those located in the distributors of fertilizers and lime for shrimp farms and near the gas stations.