Exposure to mercury and polychlorinated biphenyls affects the thyroid function of an Australian seabird (Ardenna carneipes)

As top predators in the marine environment, seabirds can be exposed to high levels of persistent pollutants that can bioaccumulate and biomagnify making these predators excellent indicators of ecosystem health. Commonly found in the marine environment, mercury (Hg) and polychlorinated biphenyls (PCBs) are known to interfere with the thyroid system in wildlife. This study quantified PCBs and Hg concentrations and investigated the relationship with thyroxine (T4) and triiodothyronine (T3) levels, in fledgling and adult sable shearwaters (Ardenna carneipes). Hg and PCBs were measured in feathers and red blood cells, respectively. The results indicate Hg and PCBs were more abundant in adult shearwaters than in fledglings. Negative associations were found between Hg/PCB body burdens and circulating thyroid hormone concentrations in both age categories. However, some of these correlations were not statistically significant. This study presents an empirical dataset of these contaminants and the thyroid function of adult and juvenile birds. This is a significant step towards better understanding the threat posed by Hg and PCBs to the health of seabirds.