Ecotoxicological effects of innovative wood protection treatments on freshwater bioindicator organisms

The protection of wooden structures used in aquatic environments is of paramount importance to prevent their attack by xylophagous organisms. With the aim of testing innovative and more eco-friendly wood treatments for the freshwater environments, we evaluated the possible ecotoxicological effects of Picea abies wood panels differently treated with copper-based formulation and thermal modification. The toxicity of the treatments was evaluated through exposure experiments by applying the biomarker approach in two freshwater bioindicators: the bivalve Dreissena polymorpha and the gastropod Theodoxus fluviatilis. The organisms were kept for 4 weeks in experimental tanks under semi-static conditions of the following: control (no panels), NTC (untreated panels), TT (thermally treated panels), and S-UC3 (panels treated with Cu-based formulation). Biomarkers in mussels exhibited no toxic effects attributable to NTC and TT conditions. The biological responses of the gastropods registered some stress signals not related to leaching process. Panels treated with the S-UC3 formulation caused 100% mortality of gastropods and damage effects in mussels. These responses were consistent with copper released in the water, which reached a concentration higher than 200 ppb. The study highlighted the need to improve the rinsing/maturation phase in wood panel impregnation protocols, to remove the Cu fraction easily released in freshwater environment. T. fluviatilis exhibited excessive sensitivity under microcosm conditions, indicating its unsuitability as a bioindicator in standardized aquarium exposure experiments.