Understanding Mercury Contamination: Management and Testing Recommendations for the Disposal of Dredged Sediments at the LA-3 Ocean Dredged Material Disposal Site
Mercury (Hg), a neurotoxicant released primarily by anthropogenic activity, is present in all the world’s oceans, estuaries, and freshwater bodies (Giang, 2013). In addition to its toxicity to marine biota, Hg bioaccumulates within fish and other seafoods, presenting a threat to human health since fish remain important sources of protein for people across the world (Giang, 2013). Despite improvements in Hg pollution control, levels in commonly consumed marine fish such as bluefin tuna often exceed human health guidelines causing recommendations to limit fish consumption (Giang, 2013). Organic forms of Hg, such as monomethylmercury (MMHg), are more toxic than other forms and are the main causes of concern for human and ecosystem health. Various forms of Hg can transform into MMHg overtime and in certain environments. Elemental mercury (Hg(0)) can transform into different chemical species before becoming MMHg while divalent mercury (Hg(II)) can transform into MMHg through biotic methylation in the water column and sediments under specific chemical and physical conditions (Ming et al., 2019).
The U.S. Environmental Protection Agency (EPA) manages approximately 98 ocean dredged material disposal sites (ODMDS) around the country’s federal waters. Disposal sites are used for the disposal of nontoxic sediments that are routinely removed to maintain navigational depths in ports, harbors, and marinas, as well as to support national maritime commerce, commercial fisheries, and recreation (EPA, n.d.). The U.S. Army Corps of Engineers (USACE) is planning to dredge federal channel segments in Newport Bay in Newport Beach, California. Based on sediment samples collected and analyzed for ocean disposal testing, the USACE project sediments were found to be high in Hg contamination (Anchor QEA, LLC., 2020). However, despite the high Hg levels, toxicity tests indicated suitability for ocean disposal at EPA’s LA-3 ODMDS located offshore of Newport Bay (Anchor QEA, LLC., 2020). The current Hg levels at the LA-3 disposal site are low to non-detect, and the effects of disposing of sediments loaded with Hg from the Federal channel in Newport Bay are unknown (Battelle and DAMOSVision, 2015). To address this issue, a literature review of Hg biogeochemical cycling and Hg-methylation was conducted to assist in the understanding of Hg speciation and transport. A policy review was also completed to assess the policies relevant to sediment dredging in California and ocean dumping in federal waters. Related to the policies in place, manuals utilized by USACE and EPA for testing and analysis purposes were reviewed to determine additional sediment and water column tests to minimize the potential risk of Hg contamination in the marine environment. Through the compilation of information, testing and analysis recommendations in addition to current testing were made for the dredge and disposal site locations.