Type of Presentation

Oral

Session Title

General contaminant toxicology in aquatic and terrestrial species

Description

Eggs of marine birds are used widely to monitor environmental mercury because they are relatively easy to collect and integrate a signal from the entire food web. Trends in mercury from seabird eggs, however, may represent variation in diet rather than variation in mercury availability; due to biomagnification, seabirds switching to feed at a higher trophic level will usually have higher mercury levels. We measured mercury concentrations in eggs from six seabird species in Pacific Canada during the period 1968-2012. In contrast to expectation, storm-petrels feeding partially on invertebrates had the highest mercury burden while herons feeding on large fish had the lowest mercury burden. Rather than correlating with trophic level (δ15N), mercury levels correlated with δ34S (R2 = 0.86). For cormorants, the only group showing a significant temporal mercury trend, both mercury and δ34S decreased over time. Sulfate-rich environments (high δ34S) are occupied by sulfate-reducing bacteria that produce methylmercury, and we hypothesize that variation in mercury within and among seabirds is associated with variation in methylmercury production by sulfate-reducing bacteria at the base of the food web. Variation in mercury levels in seabirds across space and time were associated with the origin of sulfur in the diet.

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Long term trends in mercury in seabird eggs from Pacific Canada: relationships with stable isotopes particularly sulfur

2016SSEC

Eggs of marine birds are used widely to monitor environmental mercury because they are relatively easy to collect and integrate a signal from the entire food web. Trends in mercury from seabird eggs, however, may represent variation in diet rather than variation in mercury availability; due to biomagnification, seabirds switching to feed at a higher trophic level will usually have higher mercury levels. We measured mercury concentrations in eggs from six seabird species in Pacific Canada during the period 1968-2012. In contrast to expectation, storm-petrels feeding partially on invertebrates had the highest mercury burden while herons feeding on large fish had the lowest mercury burden. Rather than correlating with trophic level (δ15N), mercury levels correlated with δ34S (R2 = 0.86). For cormorants, the only group showing a significant temporal mercury trend, both mercury and δ34S decreased over time. Sulfate-rich environments (high δ34S) are occupied by sulfate-reducing bacteria that produce methylmercury, and we hypothesize that variation in mercury within and among seabirds is associated with variation in methylmercury production by sulfate-reducing bacteria at the base of the food web. Variation in mercury levels in seabirds across space and time were associated with the origin of sulfur in the diet.