A "toxic trio" (mercury, lead and cadmium) metal assessment in marine commercial species from Northwestern Mediterranean Sea : risk and recommendations

Mercury (Hg), lead (Pb), and cadmium (Cd), commonly termed "the toxic trio," are highly toxic metals regulated in food by the European Union for consumer safety. This study examined the biological and environmental factors influencing their accumulation in marine organisms by analyzing trace metal concentrations in the muscle tissue of 10 species with varied habitat preferences (seven teleosts, two elasmobranchs, and one crustacean) caught in the Northwestern Mediterranean. Shark samples across different size ranges were analysed to identify accumulation patterns. Geographical variability was evaluated using the small-spotted catshark (Scyliorhinus canicula) as a biomonitor, comparing Mediterranean results with data from Atlantic Spanish regions and published values. Compliance with European regulations and associated consumer risks were also assessed. Hg accumulation showed interspecific variation linked to habitat use, with the highest levels in benthic species, and intraspecific accumulation positively correlated with size. Geographically, Hg levels were higher in the Northwestern Mediterranean, reflecting the region's high methylation potential. While Pb and Cd remained within European consumption limits, over one-third of benthic samples exceeded Hg thresholds, and 92.45 % of adult sharks surpassed safe levels, compromising their commercialization. Mediterranean benthic fish should be consumed sparingly, particularly by pregnant women and children, as recommended for top predator species. This study highlights how habitat use and body size drive Hg accumulation, establishes S. canicula as a biomonitor for contamination, and underscores the role of regional environmental factors in shaping metal distribution and bioavailability, contributing to a better understanding of Hg fate in marine ecosystems and its potential impact.