Effects of ash-loaded post-fire runoff on the freshwater clam Corbicula fluminea

•The impacts of wildfires on the freshwater clam Corbicula fluminea were assessed.•Aqueous extracts of ash (AEA) were used to represent ash-loaded post-fire runoff.•The bio-concentration ability of the clam was assessed in a filtration experiment.•Post-fire loads (rich in metals and PAHs) can compromise clams survival.

Wildfires, increasingly frequent and severe in the Mediterranean countries, can cause serious impacts on ecosystems. As a diffuse source of contaminants – namely inorganic elements (metals, metalloids and non-metallic elements) and polycyclic aromatic hydrocarbons (PAHs) – post-fire runoff may cause toxic effects on the aquatic biota. Despite the recognition of these likely impacts, this issue has been still largely neglected. This study explores the impacts of ash from wildfires on the freshwater clam Corbicula fluminea and the ability of this filter feeder to concentrate the contaminants associated with ash in post-fire runoff. The bio-concentration potential of the clam was assessed in a 7-day filtration experiment, using aqueous extract of ashes (AEA) to represent post-fire runoff. Despite the noticeable mortality of the clams exposed to the AEA (∼30% higher in AEA than in control after 7 days of exposure), there was a clear reduction on the concentration of almost all pyrolytic substances in the water linked to bio-filtration and bio-concentration activity. Along 7 days the clams operated decreases of more than 70% for some chemicals (Cu, Mn and Zn) while others were no longer detected in the water at the end of the experiment (Cr, NAP and PHE). The removal from water was accompanied by contaminants’ accumulation in clams’ soft tissues and, less extensively, in shells. Lower pollutant loads of filtered AEA translated into decreased toxicity of the matrix towards standard aquatic species (microalgae, macrophytes and cladocerans) confirming an improvement as well in the biological quality of the water through bio-filtration. Although post-fire loads can compromise C. fluminea survival, this study evidenced the potential of this invasive species to contribute to water quality improvement.