First concurrent assessment of elemental- and organic-contaminant loads in skin biopsies of whale sharks from Djibouti

The Gulf of Tadjoura (Djibouti) is an important site where the whale shark (Rhincodon typus Smith, 1828) aggregates seasonally. Because of the proximity to the port of Djibouti that is located along one of the busiest shipping areas in the world, whale sharks are potentially exposed to relatively high levels of trace elements and organochlorines. To assess their contamination status, concentrations of 15 trace elements, DDTs and PCBs were concurrently assessed for the first time in skin biopsies of 20 whale sharks. Additionally, 12 zooplankton samples were collected and analyzed for trace elements content. Concentration of As, Cu, Zn and Se were higher than in previous studies on this species. Whale shark samples exceeded the maximum allowable limits for foodstuffs for Cr, Pb Se, Cd and Zn. Results from this study suggests that Cr, Ni and Mo may biomagnify in this species. With regard to PCBs, the predominant congener were Tetra-CB, accounting for 41% of total PCBs and Penta-CB for 23%, while for DDTs, the predominant metabolite was DDE contributing for 51% of total compounds. The maximum residue limit for DDTs and for the ind-PCBs in fish set by U.S. EPA and by the EU regulation, respectively, was exceeded in 62% of whale sharks. Moreover, the p,p′DDE/ΣDDT ratios were higher than the critical value of 0.6, indicating possible recent inputs of technical DDTs in the area. This study suggests some concerns for the contamination status of whale sharks in Djibouti and, since major threats for this species include bycatch and illegal fisheries, highlights some level of risk from the exposure to elemental- and organic-contaminant via shark consumption.