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Mercury concentrations in Seaside Sparrows and Marsh Rice Rats differ across the Mississippi River Estuary

July 24, 2024

Mercury (Hg) concentrations and their associated toxicological effects in terrestrial ecosystems of the Gulf of Mexico are largely unknown. Compounding this uncertainty, a large input of organic matter from the 2010 Deepwater Horizon oil spill may have altered Hg cycling and bioaccumulation dynamics. To test this idea, we quantified blood concentrations of total mercury (THg) in Seaside Sparrows (Ammospiza maritima) and Marsh Rice Rats (Oryzomys palustris) in marshes west and east of the Mississippi River in 2015 and 2016. We also tested for a difference in THg concentrations between oiled and non-oiled sites. To address the potential confounding effect of diet variation on Hg transfer, we used stable nitrogen (δ15N) and carbon (δ13C) isotope values as proxies of trophic position and the source of primary production, respectively. Our results revealed that five to six years after the spill, THg concentrations were not higher in sites oiled by the spill compared to non-oiled sites. In both species, THg was higher at sites east of the Mississippi River compared to control and oiled sites, located west. In Seaside Sparrows but not in Marsh Rice Rats, THg increased with δ15N values, suggesting Hg trophic biomagnification. Overall, even in sites with the most elevated THg, concentrations were generally low. In Seaside Sparrows, THg concentrations were also lower than previously reported in this and other closely related passerines, with only 7% of tested birds exceeding the lowest observed effect concentration associated with toxic effects across bird species (0.2 µg/g ww). The factors associated with geographic heterogeneity in Hg exposure remain uncertain. Clarification could inform risk assessment and future restoration and management actions in a region facing vast anthropogenic changes.

Publication Year 2024
Title Mercury concentrations in Seaside Sparrows and Marsh Rice Rats differ across the Mississippi River Estuary
DOI 10.1007/s10646-024-02789-1
Authors Andrea Bonisoli-Alquati, Allyson K. Jackson, Collin A. Eagles-Smith, Sydney Moyo, Anna A. Pérez-Umphre, Michael J. Polito, Allison M. Snider, S. Tyler Williams, Stefan Woltmann, Philip C. Stouffer, Sabrina S. Taylor
Publication Type Article
Publication Subtype Journal Article
Series Title Ecotoxicology
Index ID 70256190
Record Source USGS Publications Warehouse
USGS Organization Forest and Rangeland Ecosystem Science Center
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