Metal Fractionation in Marine Sediments Acidified by Enrichment of CO: A Risk Assessment

Carbon-capture and storage is considered to be a potential mitigation option for climate change. However, accidental leaks of CO can occur, resulting in changes in ocean chemistry such as acidification and metal mobilization. Laboratory experiments were performed to provide data on the effects of CO-related acidification on the chemical fractionation of metal(loid)s in marine-contaminated sediments using sequential extraction procedures. The results showed that sediments from Huelva estuary registered concentrations of arsenic, copper, lead, and zinc that surpass the probable biological effect level established by international protocols. Zinc had the greatest proportion in the most mobile fraction of the sediment. Metals in this fraction represent an environmental risk because they are weakly bound to sediment, and therefore more likely to migrate to the water column. Indeed, the concentration of this metal was lower in the most acidified scenarios when compared to control pH, indicating probable zinc mobilization from the sediment to the seawater.