Eggs from egrets (Egretta thula) were collected from Cartagena Bay and Totumo Marsh, two sites at the north of Colombia with different pollution background, and measured their morphometric parameters as well as total mercury (T-Hg) and calcium levels in eggshell. Statistically significant differences were observed for egg weight and size between the two sampling locations. T-Hg and calcium concentrations in eggshell were greater in eggs from Cartagena Bay, the industrial site, compared to Totumo Marsh, a non-industrial location. The opposite was observed for eggshell thickness (3.6% less in the bay). Pearson correlation analysis showed eggshell T-Hg negatively correlated with eggshell weight in eggs from the marsh (R=-0.795, P<0.006), but not from the bay (R=0.387, P=0.269), probably suggesting greater susceptibility to Hg in birds from the non-polluted site. In short, results suggest eggs from E. thula at Cartagena Bay have greater T-Hg concentrations and less eggshell thickness than those from Totumo Marsh.
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