Citation:

Janssen, S., K. Patnode, Bruce R Pluta, AND D. Krabbenhoft. Insights into Mercury Source Identification and Bioaccumulation Using Stable Isotope Approaches in the Hannibal Pool of the Ohio River, USA. Integrated Environmental Assessment and Management. Allen Press, Inc., Lawrence, KS, 17(1):233-242, (2021). https://doi.org/10.1002/ieam.4308

Impact/Purpose:

Mercury hazardous waste site remediation and restoration are challenging to address for two reasons: (1) unlike man-synthesized compounds (for example DDT, PCBs, PAHs, etc…) that with time will diminish in their impact, mercury is an element and will not decompose; and (2) in most locations, our ability to prescribe effective restoration actions are severely hampered by the presence of multiple sources of mercury. Other sources to surface waters include watershed runoff, NPDES permits, other hazardous waste sites, and deposition of atmospheric mercury from point and non-point sources. However, the lack of an ability to “fingerprint” which sources are most impactful to local food webs has remained unavailable, and resulted in a significant hindrance toward prescribing effective mitigation strategies. Fish consumption advisories for mercury have been warranted for many rivers and lakes nationwide for many years and will only be reduced or eliminated if the primary sources of mercury are controlled. To date, effective control actions have been severely hampered by the presence of multiple sources of mercury, their relative contributions to fish contamination unknown. A prime example is the Ohio River where mercury fish tissue concentrations increased from 2001 to 2008 (Ohio EPA) and yet discharges were permitted to increase from 61 pounds in 2007 to 380 pounds in 2013 (EPA Toxic Release Inventory) and mixing zone variances for mercury are still being granted (Ohio River Valley Water Sanitation Commission). In the Hannibal Pool of the Ohio River, Hanlin-Allied-Olin Superfund site (HAO), PPG Industries (PPG; now Axiall), Mitchell Coal-fired Power Plant (MPP), non-point source watershed runoff, and regional atmospheric deposition are all likely contributors to the mercury contamination. The remedial investigation for the Superfund site and the RCRA investigation for Axiall include determining the extent of contamination and risk from mercury in the river. Without a means to quantify the relative contributions from the multiple sources, EPA’s ability to potentially address contaminated sediments, and recommend more stringent mercury criteria in NPDES discharge limits, or reductions in air emissions is impacted. Thus, efforts to improve water quality in the river and reduce fish contamination cannot be implemented. Similar scenarios occur in most EPA Regions and states where attribution of mercury contamination from multiple sources cannot be determined. USGS has newly acquired the analytical equipment to measure the stable isotopic fractionation of mercury. The highly specialized instrument used for this analysis (Multicollector Inductively Coupled Plasma-Mass Spectrometer or MC ICP-MS) has previously only been utilized within a handful of academic labs throughout North America. With the USGS now capable of this analysis, it opens an important door towards applying this powerful tool within a regulatory context. This analytical capability has recently been applied to study the broad scale attribution patterns in the Great Lakes at the request of the EPA Great Lakes National Program Office. The study demonstrated the exceptional value of this technique in these large lakes. Validation of this technique in flowing waters (rivers and streams) and smaller lakes is warranted to demonstrate its applicability to sites in locations with multiple point and non-point sources of mercury. This technique is especially promising at sites containing large relic mercury inventories from industrial sources that more than likely have a different mercury signature than current atmospheric mercury. With the ability to apportion mercury sources, the project team can more effectively develop and evaluate remedial, enforcement, and permitting options to reduce mercury exposure and risk.

Description:

Mercury contamination in river systems due to historic and current Hg releases is a persistent concern for both wildlife and human health. In larger rivers, like the Ohio River, USA, it is difficult to directly link Hg discharges to bioaccumulation due to the existence of multiple industrial Hg sources as well as the varied dietary and migratory habits of biota. To better understand how industrial effluent influences the cycling and bioaccumulation of Hg within the Ohio River, Hg stable isotope analysis was applied to various nonbiological and biological media. High Hg concentrations in suspended particulate matter suggest this vector was the largest contributor of Hg to the water column, and distinct Hg source signatures were observed in effluent particulates from different industrial processes, such as chlor‐alkali activity (δ202Hg = −0.52‰) and coal power plant discharge (δ202Hg = −1.39‰). Despite this distinction, average sediments (δ202Hg = −1.00 ± 0.23‰) showed intermediate isotopic signatures that suggest the accumulation of a mixed Hg source driven by multiple industrial discharges. Biota in the system were shown to have a conserved range of δ202Hg and estimation approaches related these signatures back to particulate matter within Hannibal Pool. Mussels were found to conserve Hg isotopes signatures independently of food web drivers and served as ideal water column indicators of bioaccumulated Hg sources. This study highlights the complexity of Hg cycling within an industrialized river and shows that an isotope tracer approach can provide insight to water column sources of Hg. Integr Environ Assess Manag 2021;17:233−242. Published 2020. This article is a US Government work and is in the public domain in the USA.

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