Evaluation of the threat of marine CO₂ leakage-associated acidification on the toxicity of sediment metals to juvenile bivalves

Highlights: • Short-term tests using juveniles of bivalves to study the effects of CO₂ dissolved. • CO₂ causes effects if the threshold concentration of the organism is overlapped. • Flows of escaped CO₂ would affect the geochemical composition of sediment–seawater. • CO₂-induced acidification would affect differently to marine sediment toxicity. - Abstract: The effects of the acidification associated with CO₂ leakage from sub-seabed geological storage was studied by the evaluation of the short-term effects of CO₂-induced acidification on juveniles of the bivalve Ruditapes philippinarum. Laboratory scale experiments were performed using a CO₂-bubbling system designed to conduct ecotoxicological assays. The organisms were exposed for 10 days to elutriates of sediments collected in different littoral areas that were subjected to various pH treatments (pH 7.1, 6.6, 6.1). The acute pH-associated effects on the bivalves were observed, and the dissolved metals in the elutriates were measured. The median toxic effect pH was calculated, which ranged from 6.33 to 6.45. The amount of dissolved Zn in the sediment elutriates increased in parallel with the pH reductions and was correlated with the proton concentrations. The pH, the pCO₂ and the dissolved metal concentrations (Zn and Fe) were linked with the mortality of the exposed bivalves