Examining Mercury Transfer in the American Alligator
Stephen E. Long, Tracey B. Schock, Nilsen Frances
Prenatal exposure to environmental contaminants can cause developmental issues in humans and wildlife. Mercury (Hg) is particularly detrimental, often impairing the organization and development of important organ systems by causing irreparable damage. Wildlife species that are environmentally exposed to elevated Hg are useful in modeling human exposure. A common sentinel for contaminant exposure, the American alligator, was examined for Hg transfer to the developing embryos in a series of experiments. The presence of total Hg (THg) was determined in alligator egg yolk from Yawkey Wildlife Center, SC, Lake Apopka, FL, and Lake Woodruff, FL. The mean [THg] observed were 26.3 ng/g ± 11.0 ng/g, 8.8 ng/g ± 5.1 ng/g, 22.6 ng/g ± 6.3 ng/g, respectively. Maternal transfer was examined by measuring THg in nesting female blood, corresponding egg yolk, and embryo samples across three years from Yawkey Wildlife Center. We observed ~12% of the maternal [THg] in egg yolk, with 66% of the overall variation between the samples explained by correlation (rho=0.66; p<0.0001). The correlation equation (y = 0.138x 2.5534) was used to extrapolate maternal transfer at other locations and further evaluate alligators as developmental model for embryonic Hg exposure. The developmental compartmentalization of topically applied THg was examined using eggs collected from Lake Woodruff, a low Hg site. Through this analysis, we observed that Hg transfer is unlikely after calcification. The nest-specific [THg] that persisted through the dosing experiment further indicates that maternal transfer is occurring. To assess environmental Hg transfer, nest materials were evaluated for THg, however there was no relationship found with paired yolk THg.