Mercury Accumulation and Tissue Distribution in Waterbirds Overwintering in Texas
Date
2022-05
Authors
Krebs, Kyle R.
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Abstract
Mercury (Hg) is global pollutant that is toxic to wildlife at low concentrations. In waterbirds, exposure to Hg has resulted in altered breeding behavior, reduced hatching success, and nest abandonment. There have only been a few studies which assessed Hg concentrations in waterbirds in Texas, despite Texas being one of the greatest Hg emitters in the U.S. and an overwintering location for migratory waterbirds. In this study, tissues (muscle, liver, breast feather, wing feather) from 16 species of waterbirds that overwinter in Texas [American coot (Fulica americana), American wigeon (Mareca americana), blue-winged teal (Spatula discors), canvasback (Aythya valisineria), gadwall (Mareca strepera), green-winged teal (Anas carolinensis), hooded merganser (Lophodytes cucullatus), lesser scaup (Aythya affinis), mottled duck (Anas fulvigula), northern pintail (Anas acuta), northern shoveler (Anas clypeata), redhead duck (Aythya americana), red-breasted merganser (Mergus serrator), ring-necked duck (Aythya collaris) sandhill crane (Antigone canadensis), and wood duck (Aix sponsa)] were collected by TPWD licensed hunters from nine locations throughout the state and analyzed for total mercury (THg) using a direct mercury analyzer. This study investigated THg concentrations among species, foraging guilds (granivore, herbivore, omnivore, herbivore), and feeding strategies (dabbler, diver, dabbler/diver, wader) to determine which tissues and species had the greatest THg concentrations, which species had methylmercury (MeHg) concentrations exceeding federal [EPA; 0.3µg/g wet weight (ww)] and state (TDSHS; 0.7 µg/g ww) advisory levels for human consumption, and which species had THg concentrations above known threshold levels for adverse biological effects in birds. This study also investigated the relationship between δ13C and δ15N and muscle THg concentrations, and lastly investigated if wing or breast feather THg concentrations could be used to predict muscle and liver THg concentrations. Overall, THg concentrations were greatest in piscivorous diving waterbirds such as hooded merganser and red-breasted merganser but were also elevated in northern shoveler (omnivorous dabbler) and lesser scaup (omnivorous diver). Seven of the 16 investigated species had THg concentrations in their muscle and/or liver tissue that put them at risk of experiencing adverse biological effects. These same species also exceeded EPA and TDSHS MeHg advisory levels for human consumption. Wing and breast feather THg concentrations did not successfully predict muscle or liver THg concentrations in gadwall or redhead duck. The results from this study indicate that Hg accumulates the most in species that primarily consume fish but can be above concentrations known to cause deleterious biological effects in non-fish-eating species. However, since all species are migratory, future studies need to investigate the extent to which Hg accumulates in tissues while overwintering in Texas.
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Keywords
Mercury, Methylmercury, Bioaccumulation, Biomagnification, Waterbird
Citation
Krebs, K. R. (2022). <i>Mercury accumulation and tissue distribution in waterbirds overwintering in Texas</i> (Unpublished thesis). Texas State University, San Marcos, Texas.