Gunnar Hansen’s research while affiliated with University of Connecticut and other places

In estuarine food webs, bivalve molluscs transfer nutrients and pollutants to higher trophic levels. Mercury (Hg) pollution is ubiquitous, but it is especially elevated in estuaries historically impacted by industrial activities, such as those in the U.S. Northeast. Monomethylmercury (MeHg), the organic form of Hg, is highly bioaccumulative and transferable in the food web resulting in the highest concentrations in the largest and oldest marine predators. Patterns of Hg concentrations in marine bivalve molluscs, however, are poorly understood. In this study, inorganic Hg (iHg), MeHg, and the total Hg (THg) in soft tissues of the northern quahogs (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), and ribbed mussels (Geukensia demissa) from eastern Long Island sound, a temperate estuary of the western North Atlantic Ocean was investigated. In all three species, concentrations of THg remained similar between the four sampling months (May, June, July, and September), and were mostly independent of animal size. In quahogs, MeHg and iHg displayed significant (p < 0.05) positive (iHg in May and June) and negative (MeHg in July and September) changes with shell height. Variability in concentrations of THg, MeHg, and iHg, both inter- and intra-specifically was high and greater in quahogs and oysters (THg: 37, 39%, MeHg: 28, 39%, respectively) than in mussels (THg: 13%, MeHg: 20%). The percentage of THg that was MeHg (%MeHg) was also highly variable in the three species (range: 10–80%), highlighting the importance of measuring MeHg and not only THg in molluscs.

Artisanal and small-scale gold mining (ASGM), energy production and other industrial inputs are a major source of anthropogenic mercury (Hg) to the aquatic environment globally, and these inputs have led to environmental contamination and human exposure. While studies have documented the effects of Hg inputs to rivers and marine waters of the West African region, estuarine waters of Cote d’Ivoire have been understudied, besides the waters surrounding Abidjan. To fill this gap, and to examine the potential for human exposure to methylmercury (MeHg), we measured the concentrations of total Hg, MeHg, and ancillary parameters in water (dissolved and particulate phases), sediment and fish to determine the extent of environmental impact and the potential for MeHg exposure for people consuming these fish. Levels of Hg and MeHg in sediment were elevated in the vicinity of the urban environment (up to 0.3 ng/g dry weight (dw) MeHg and 623 ng/g dw total Hg) and lowest in the more remote estuarine environments. Measurements of Hg in tuna and other larger pelagic coastal species indicated that levels were elevated but comparable to other North Atlantic regions. However, levels of Hg in fish, even smaller estuarine species, were such that the rural and urban populations are potentially being exposed to unsafe levels of MeHg, primarily as a result of the relatively high fish consumption in Cote d’Ivoire compared to other countries. Overall, both local point sources and the transport of Hg used in interior ASGM activities are the sources for Hg contamination to these coastal waters.

Mercury (Hg) bioaccumulates and exerts toxic effects on freshwater fish upon assimilation into tissues. The Still River, USA, was subjected to severe Hg pollution as a result of the 19th century hat-making industry. Our objective was to determine if the legacy Hg pollution from the hat industry continues to manifest as elevated Hg in the environment (sediment, water, and suspended particulates) and in the muscle and liver of fish from the Still River watershed. Rhinichthys atratulus (Eastern Blacknose Dace), a freshwater fish that display high site fidelity, was chosen as an indicator of total (THg) and methyl (MeHg) mercury bioavailability at four legacy polluted sites, and three reference sites. Still River legacy sites had significantly higher (p ≤ 0.0001) concentrations of THg in surface sediments (134.69 ng/g dw – 1990.00 ng/g dw) compared to reference sites (25.45 ng/g dw – 48.39 ng/g dw). Surprisingly, the average levels of THg in fish muscle were significantly lower (p ≤ 0.04) for fish from the majority of legacy sites (0.36 μg/g ww – 0.39 μg/g ww) compared to the majority of reference sites (0.47 μg/g ww – 0.52 μg/g ww). There was no significant difference (p ≥ 0.15) among liver THg concentrations for most sites and there was no significant relationship found (p ≥ 0.09) between either tissue type an any environmental parameters. Our results demonstrate that the presence of legacy Hg pollution does not directly translate into enhanced MeHg accumulation in fish.