Mercury Found in Birds Across Western North America

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A recent landscape-scale study has documented mercury in birds throughout western North America, identifying hotspots and large-scale ecological attributes that influence mercury exposure and accumulation in birds.

This article is part of the August-September 2016 issue of the Sound Waves newsletter.

Map of North America shows dots where birds have been found, with varying levels of mercury in their blood.

Blood-equivalent total mercury (THg) concentrations in birds across western North America using original data (n=27,629 individual samples). All individual data points are shown, with lower THg concentrations in the background as larger symbols and higher THg concentrations as smaller symbols on top.

A recent landscape-scale study by USGS and U.S. and Canadian collaborators has documented mercury in birds throughout western North America, identifying hotspots and large-scale ecological attributes that influence mercury exposure and accumulation in birds. This is the first study to combine toxicity benchmarks developed for different bird tissues into an overall assessment of mercury’s risk to birds.

Mercury concentrations differed among species, foraging guilds, habitat types, locations, and ecoregions and were greatest in ocean and salt marsh habitats, followed by freshwater habitats, and lowest in terrestrial habitats (see chart below). Birds that ate fish or other animals had the greatest mercury concentrations, whereas birds that ate plants and seeds exhibited the lowest mercury concentrations.

This study used a new model to translate published mercury toxicity benchmarks across bird tissues into a common blood-equivalent mercury concentration. Scientists identified four general toxicity benchmarks for mercury contamination in birds. The analysis included 30,000 samples from 225 species and, using data from 200 scientific publications, incorporated an additional 2,000 mean mercury concentrations, representing 20,000 individuals and 176 species.

Overall, using blood-equivalent mercury concentrations, 66% of birds sampled in western North American exceeded the lowest-observed effect level (0.2 µg/g wet weight), 28% exceeded moderate risk (1.0 µg/g wet weight), 8% exceeded high risk (3.0 µg/g wet weight), and 4% exceeded severe risk (4.0 µg/g wet weight). The map below shows the distribution of mercury concentrations in birds throughout western North America.

Plot shows how levels of mercury found in the blood of birds varies by bird habitat.

Blood-equivalent total mercury concentrations in birds among habitats in western North America (n=27,629 individual samples; data shows least squares means ± standard errors).

Methylmercury contamination of the environment is an important issue globally and birds are useful bioindicators for environmental contamination. Landscape-scale assessments of environmental pollution can be helpful for understanding the major drivers and distributions of contaminants in animals, prioritizing contaminant monitoring and remediation programs, focusing policy-making decisions, and evaluating the health of species of concern.

This work was conducted as a part of the Western North American Mercury Synthesis Working Group supported by the John Wesley Powell Center for Analysis and Synthesis, funded by the USGS with additional support from the USGS Ecosystems Mission Area and Contaminant Biology Program.

The full citation for the publication is:

Ackerman, J.T., Eagles-Smith, C.A., Herzog, M.P., Hartman, C.A., Peterson, S.H., Evers, D.C., Jackson, A.K., Elliott, J.E., Vander Pol, S.S., Bryan, C.E., 2016, Avian mercury exposure and toxicological risk across western North America—A synthesis: Science of The Total Environment, doi: 10.1016/j.scitotenv.2016.03.071.

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Date published: September 30, 2016

Sound Waves Newsletter - August-September 2016

USGS helps the Government of India discover large, highly enriched, producible accumulations of natural gas hydrate in the Bay of Bengal, USGS re-evaluates the causes and hazards of South Carolina earthquakes, and more in this August-September issue of Sound Waves.