Long- term effects of water quality on the freshwater bivalve Diplodon chilensis (Unionida: Hyriidae) caged at different sites in a North Patagonian river (Argentina)

Water quality was monitored along an Andean river of global importance using the freshwater bivalve Diplodon chilensis as sentinel species. Bivalves were placed in cages at three sites (S1-3) in the Chimehuin River in order to evaluate the long-term effects of a trout hatchery (S2) and the open dump and sewage treatment plant of a nearby city (S3). Water samples and bivalves were collected at 0, 3, 6, 9 and 12 months, from S3, S2 and from a reference site upstream (S1), and physicochemical parameters and the biological response of the caged bivalves were studied. ROS production, antioxidant response, oxidative damage, energy status and morphometric ratios were included as response biomarkers. Most of biomarkers showed site and time dependence including bivalves transplanted at S1, revealing natural variability. Both anthropogenic perturbed sites (S2 and S3) showed differences in the exposed bivalves with respect to the reference site (S1) in their biomarker responses after 9 and 12 months of exposure (July and September, respectively). Multivariate analysis showed alterations in hemocytes (ROS, TOSC and NRRT50), in energy balance in digestive gland (energy and DGF) and in the detoxification response (GST) and GSH values in gill when bivalves were exposed to hatchery waste; whereas metal and bacterial pollution (S3 in July) caused GSH increase and a reduction of lysosomal damage in hemocytes. Results show that changes in the water quality of Chimehuin River due to the anthropogenic impact can be detected using the biomarkers analysed on D. chilensis, being a useful tool for studies of long-term monitories.