Fluoride exposure and selected characteristics of eggs and bones of the herring gull (Larus argentatus) and the common gull (Larus canus).

Fluorine concentrations were determined in the shell of 285 herring gull eggs (Larus argentatus) and 120 common gull eggs (Larus canus), collected May 1991 to 1993, from breeding colonies exposed to emissions from two Norwegian primary aluminum smelters located at Karmøy and Sunndal, and from unexposed reference localities in Eigersund, Sola, and Stavanger. Volume-index, shell thickness, thickness-index, and fertilization of the eggs also were monitored. In both species, the shell fluorine concentration was significantly increased in eggs collected at sites exposed to fluoride emissions. No effects on other egg characteristics were observed. In both exposed and unexposed sites, the last-laid egg in a clutch, normally containing three eggs, had the highest shell fluorine residue. Fluorine levels also were analyzed in femurs from 42 herring gulls, collected from Karmøy and Sola in May 1993. The relationship between sex and fluoride accumulation, and the relations between fluorine concentration in femurs of laying herring gulls and in the shell of their eggs, were evaluated. Bone morphology also was studied. Bone fluorine concentrations were raised significantly in emission-exposed female birds. Moreover, females from the exposed site had significantly higher fluorine residues than males. There was a positive correlation between fluorine levels in femurs of individual laying birds and those in the shells of their eggs. No changes in bone morphology due to fluoride exposure was found.