Trace elements and POPs in baitfish from Madagascar: Implications for whale shark and human exposure

The rapid increase of human activities is threatening the ocean biodiversity, with marine vertebrates, particularly elasmobranchs, facing higher extinction risks. Among them, the whale shark (Rhincodon typus), an endangered migratory filter-feeding species, is threated by multiple anthropogenic pressures, including marine pollution. This study focuses on determining the presence and levels of legacy contaminants (PCBs, DDT) and trace elements (TEs) in baitfish, a primary prey species of whale sharks in Madagascar, and assessing the potential risks to whale sharks and humans through the consumption of contaminated baitfish (Sardinella gibbosa). Results indicate that while levels of DDT were below environmental safety thresholds, Hg levels in baitfish exceeded the acceptable limit, posing significant bioaccumulation risks to higher trophic level organisms, including whale sharks. Furthermore, comparisons with established maximum allowable limits for foodstuffs consumption revealed that Sardinella gibbosa may pose both non-carcinogenic and carcinogenic health risks to humans, particularly for pollutants like PCB, Cd, Ni, and Hg. This research highlights the importance of considering baitfish consumption as a significant pathway for pollutant uptake in whale sharks, suggesting that their exposure may be far higher than previously estimated through zooplankton alone. These findings underscore the critical need for continued monitoring of chemical pollution in coastal ecosystems, which are vital hotspot for global marine biodiversity, particularly in regions like Madagascar, where pollution from industrial, agricultural, and mining activities exacerbates the risk to both marine biodiversity and human health.