2 Estimating methylmercury concentrations in aquatic food webs: Implications of variable biomagnification factors and primary consumer concentrations

Thursday, August 6, 2009: 8:20 AM
Sendero Blrm II, Hyatt
Stephanie N. Schmidt , Environmental Studies & Biology, St. Olaf College, Northfield, MN

Fish consumption advisories due to mercury contamination are widespread throughout the United States.  Mercury accumulates in tissues with each trophic transfer, resulting in biomagnification of the toxic contaminant throughout the food web.  A review of studies revealed highly variable biomagnification factors (BMFs) for mercury across a variety of aquatic systems.  Furthermore, the bioavailability of mercury is dependent upon environmental factors that can cause temporal and spatial variation in concentrations of mercury in primary consumers.  The variability of both BMF values and primary consumer mercury concentrations could have major implications for estimating mercury concentrations in upper trophic levels.  The ability to predict mercury concentrations across a trophic continuum is evaluated, using the variability of calculated BMF values and mercury concentrations of primary consumers, as reported in the literature.  A simplified model and bootstrapping techniques allowed for calculation of mean methylmercury concentrations with 95% confidence intervals across multiple trophic levels.   


As trophic position increased, mean methylmercury and variability around the mean dramatically increased, especially beyond the fourth trophic level.  A benthic-based food web had slightly lower mean methylmercury and variability around the mean.  In fact, a benthic-based food web resulted in the mean methylmercury concentrations below the FDA consumption limit of 1 ppm across all trophic levels.  Whereas, the 95% confidence intervals for a pelagic-based food web exceeded 1 ppm beyond a trophic level of 4.5.  The results presented here suggest that the lengthening of the food chain due to non-native species could cause higher trophic levels to include the FDA 1 ppm consumption limit within a 95% confidence interval.  Furthermore, non-native species that would cause top predators to shift from a benthic to a pelagic food source could dramatically increase the biomagnification potential of mercury.

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