Caddis larvae (Trichoptera, Hydropsychidae) indicate delaying recovery of a watercourse polluted by pulp and paper industry

We studied ecotoxicological responses of aquatic insects to evaluate the recovery of a watercourse with a history of over 100 years as a recipient of pulp and paper mill effluents. The recovery of the water quality began in 1985 due to the improved technology, but ecotoxicological effects on biota have still been evident two decades later, as indicated by morphological abnormalities in tracheal gills of caddis larvae. We hypothesized that these abnormalities are related to organic contaminants, such as resin acids, alkylated PAHs and chlorinated organic compounds, released historically from the mills, and more recently via resuspension from the sediment. Samples were collected between 1999 and 2008, and the species composition and morphological abnormalities in the gill tufts were analysed. We tested a Hydropsychidae index (HA) based on species sensitivity scoring as an indicator of improved overall water quality, especially oxygen concentrations. Gill abnormalities were used as morphological biomarkers indicating potential ecotoxicity. The increased HA values revealed improved oxygen levels and associated recovery of benthic macroinvertebrate community structure. However, the incidence of gill abnormalities remained elevated until the year 2008 indicating slow recovery, as 20-year impacts on population health and ecotoxicity was detected in the watercourse polluted by pulp and paper industry.