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

Area of Science:

• Environmental toxicology
• Ecosystem health
• Wildlife exposure assessment

Background:

• Mercury (Hg) cycling and toxicological effects in Gulf of Mexico terrestrial ecosystems are poorly understood.
• The 2010 Deepwater Horizon oil spill introduced significant organic matter, potentially altering Hg dynamics.
• Assessing Hg exposure in wildlife is crucial for understanding ecosystem impacts.

Purpose of the Study:

• To quantify total mercury (THg) concentrations in Seaside Sparrows and Marsh Rice Rats.
• To determine if oil spill sites had higher THg concentrations compared to non-oiled sites.
• To investigate the influence of diet and trophic position on Hg bioaccumulation.

Main Methods:

• Blood THg concentrations were measured in Seaside Sparrows and Marsh Rice Rats in 2015-2016.
• Stable isotopes (δ15N, δ13C) were used to assess trophic position and primary production sources.
• THg levels were compared between sites affected by the oil spill and unaffected sites.

Main Results:

• Five to six years post-spill, oiled and non-oiled sites showed no significant difference in THg concentrations.
• THg concentrations were higher in both species east of the Mississippi River compared to west.
• Seaside Sparrows showed THg increasing with trophic level (δ15N), indicating biomagnification.

Conclusions:

• The Deepwater Horizon oil spill did not appear to increase Hg concentrations in these terrestrial species.
• Geographic location east of the Mississippi River was associated with higher Hg exposure.
• Hg concentrations were generally low, with few individuals exceeding known toxic effect levels, but factors driving geographic variation require further study.