Optimizing stream water mercury sampling for calculation of fish bioaccumulation factors

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Aquatic Science

Background:

• Mercury (Hg) bioaccumulation factors (BAFs) are vital for fish monitoring and regulation.
• BAFs depend on accurate fish and water Hg concentrations, making sampling methods critical.
• Existing methods are sensitive to sampling and analysis artifacts.

Purpose of the Study:

• To identify optimal Hg(water) sampling strategies for reliable BAF calculations.
• To evaluate the impact of water sample timing, filtration, and mercury species on fish-water Hg relationships.
• To improve the accuracy of mercury monitoring in game fish.

Main Methods:

• Modeled Hg(water) concentrations using data from 11 streams/rivers across five states.
• Incorporated fish trophic position and flow-weighted Hg(water) estimates into models.
• Evaluated model parsimony using Akaike's Information Criterion, comparing different Hg species and sampling times.

Main Results:

• Filtered water methylmercury (FMeHg) and unfiltered water methylmercury (UMeHg) provided better models than filtered total mercury.
• Annual mean FMeHg models outperformed those using shorter-term averages.
• Models incorporating high FMeHg concentrations (≥80th percentile), often observed during the growing season, performed best.
• Streamflow influenced high growing-season FMeHg concentrations, with site-specific effects.

Conclusions:

• Optimized streamwater Hg sampling requires assessing site-specific FMeHg-UMeHg relationships.
• Understanding intra-annual temporal variation and streamflow-Hg dynamics is essential for accurate monitoring.
• Filtered methylmercury, sampled strategically during peak seasons and considering flow, enhances mercury assessment reliability.