Mercury Concentrations in Sentinel Fish Exposed to Contaminated Sediments Under a Natural Recovery Strategy Within the St. Lawrence River Area of Concern at Cornwall, Ontario, Canada

Abstract

Legacy mercury (Hg) sediment deposits are a long-term issue within the St. Lawrence River (Cornwall) area of concern with three depositional areas along the Cornwall, ON waterfront containing sediments that exceed the Ontario Sediment Quality Guidelines for Hg. Assessing the bioavailability of these Hg-contaminated sediments plays a crucial role in evaluating the effectiveness of the Cornwall Sediment Strategy based on a natural recovery approach. We collected specimens of fallfish (Semotilus corporalis), round goby (Neogobius melanostomus), and yellow perch (Perca flavescens) to assess spatial and temporal trends of Hg concentrations in various areas along the Cornwall waterfront, including zones of contaminated sediments and non-contaminated reference sites. This study revealed that (1) Hg concentrations in fish collected from the contaminated zones remain greater than those of fish from non-impacted locations, indicating that natural recovery is not yet achieved, (2) total Hg concentrations in yellow perch collected in 2016 were greater than those obtained during a previous assessment, indicating a reversal of the previously observed long-term declines, and (3) total Hg concentrations in yellow perch collected at the outlet of Gray's Creek compared with yellow perch from contaminated zones, suggesting other important inputs of Hg to the ecosystem than the legacy contaminated sediments.

Nearshore Sedimentary Mercury Concentrations Reflect Legacy Point Sources and Variable Sedimentation Patterns Under a Natural Recovery Strategy

“…In the CSS region, high sedimentary Hg concentrations have been positively correlated with concentrations of MeHg in benthic invertebrates (amphipods) in zone 1 (Razavi et al 2013), where elevated concentrations of Hg have also been found in spottail shiners (Choy et al 2008) and yellow perch (Fowlie et al 2008), as well as fallfish and round gobies (Lapointe and Ridal 2019). Surficial sediments have also been found to be enriched in MeHg in these areas (Delongchamp et al 2009).…”

“…This elevated surficial Hg is likely being released into the overlying water and acting as a source of bioavailable Hg to local biota (Delongchamp et al 2010). Although MeHg is a relatively small component of the total Hg signal in these sediments (<10%; Delongchamp et al 2010), as it bioaccumulates up the food web it forms a greater proportion of the Hg signal, reaching an average of 41% of the Hg signal in amphipods (Razavi et al 2013) and upwards of 80% or more in young‐of‐the‐year fish (Lapointe and Ridal 2019). Whereas many local biota have been shown to be enriched in Hg at sites with high sedimentary Hg concentrations, some have failed to find a relationship between sedimentary Hg and Hg in resident biota (both invertebrates and fish; Hodson et al 2014).…”

“…Whereas many local biota have been shown to be enriched in Hg at sites with high sedimentary Hg concentrations, some have failed to find a relationship between sedimentary Hg and Hg in resident biota (both invertebrates and fish; Hodson et al 2014). There has been some recent discussion that sediments contaminated from legacy industrial pollution may not be the sole source driving elevated Hg concentrations in fish and other biota in this aquatic ecosystem (Hodson et al 2014; Lapointe and Ridal 2019) because elevated levels of waterborne Hg have been found in local tributaries that drain wetland‐rich watersheds (Ridal et al 2010).…”