Seabirds as Biomonitors of Mercury Bioavailability in the Venice Lagoon.

Seabirds accumulate mercury (Hg) due to their long-life span together with their high trophic position. A Hg monitoring in Venice's Lagoon using three seabird species occupying different trophic habitat (Thalasseus sandvicensis, Ichthyaetus melanocephalus, and Chroicocephalus ridibundus) confirmed that fledgelings might effectively be used as sentinels of Hg bioavailability. The significant differences in Hg residues in feathers observed among the species highlighted a possible differential exposure due to different diets, with C. ridibundus accumulating more Hg than the other species. Average residues in feathers were not above the threshold associated with adverse effects on birds (5 mg kg). Nevertheless, a large part of the C. ridibundus individuals (58%) exceeded the adverse effect level, underlining the need for strengthening Hg monitoring. Seabirds indeed may provide relevant insight on Hg transfer in food webs and a better picture of the hazards to men when bird species forage on species exploited for human consumption.