A potential threat of elevated heavy metal bioaccumulation in Ruditapes decussatus by Ocean acidification

Although ocean acidification impact on calcified marine organisms such as clams and oysters have been taken seriously the last few decades, but the effect on their heavy metal bioaccumulation were not well studied. Clams are considered to be one of the most common representing example of filter feeder organisms, Since they accumulate heavy metals, they are taken as a bioindicators to monitor heavy metal pollution. This study has taken Ruditapes decussatus as an experimental model that was maintained in different levels of elevated pCO₂; 420 ppm (ambient control), 550, 750 and 1050 ppm, which IPCC represented as projected atmospheric CO₂ concentrations possible scenarios for the year 2100. Clams were incubated for a period of 36 days to be accustomed to the acidification condition as much as possible. After which they were exposed to different doses of analytical grade salts of Pb and Cu with lower concentration (1, 5 and10 µg/L) respectively and higher concentration of (100, 500 and 1000 µg/L). Both of catalase enzyme and Lipid Peroxidation, malondialdehyde assay were performed to express oxidation and heavy metal stress. The studied enzymatic activities of [catalase (CAT)] showed a consistent increase of the enzyme activity in both control 420 ppm and 550 ppm groups within lower heavy metal concentration, while in higher concentration catalase activity was increased in 750 ppm group. Furthermore, the studied lipid peroxidation [malondialdehyde (MDA)] an increase was observed within the higher heavy metal concentration in both 750 and 1050 ppm group with an average of (0.367 nmol TBARS mg prot^-1). Moreover, heavy metal concentration analysis for lower concentration of heavy metal groups recorded the highest accumulation of Pb by 550 ppm group of (0.085 µg/L) while highest Cu recorded by 1050 ppm group of (0.126 µg/L). For higher heavy metal concentration, 550 ppm group recorded highest accumulation of both Pb and Cu (0.351 and 0.529 µg/L) respectively. On the other hand, Health risk assessment was performed for all different groups and concentrations which indicating a potential threat to the seafood safety to human consumers.

Keywords: ocean acidification, pCO₂, Ruditapes decussatus, antioxidant enzymes, lipid peroxidation, bioaccumulation, Pb, Cu, Health risk assessment.