Mercury Concentrations in Water and Hybrid Striped Bass (Morone saxatilis × M. chrysops) Muscle Tissue Samples Collected from the Ohio River, USA

Abstract

We report on long-term aqueous mercury (Hg) measurements collected at fixed locations along the Ohio River, offer insights into patterns of water and fish tissue Hg levels, and calculate site-specific bioaccumulation factors (BAFs) along an extensive longitudinal basis. We examined the relationship between total recoverable Hg concentrations in water and fish samples collected from 12 locations on the mainstem Ohio River. Water samples were collected on a bimonthly basis from each location over a 6-year period preceding the collection of fish tissue samples. This abundance of data enabled us to calculate the long-term average aqueous Hg concentrations and approximate the lifetime aqueous Hg exposure experienced by fish, enabling the calculation of appropriate BAFs. Hybrid striped bass (HSB; Morone saxatilis × M. chrysops) were collected from the Ohio River, composited (three fish), and analyzed for Hg in muscle tissue from each location. Concentrations ranged from 0.2 to 0.4 mg/kg and 41.7% of all samples collected were higher than the US Environmental Protection Agency regulatory threshold of 0.3 mg Hg/kg wet weight. Hg levels generally increased with fish weight, length, and age. However, Hg concentration in the water was the strongest predictor of tissue concentrations. We found that both water and tissue concentrations increased with drainage area, albeit at different rates. This discrepancy in spatial patterns revealed that the bioaccumulation rate of methylmercury might not be consistent throughout the Ohio River mainstem. BAFs calculated at each location supported this finding, as values decreased with increasing drainage area. Our study serves to fill critical, previously identified data gaps and provides decision-makers with the information necessary to develop more appropriate BAF development and risk-management strategies.