Recovery of Mercury-Contaminated Fisheries

Abstract

In this paper, we synthesize available information on the links between changes in ecosystem loading of inorganic mercury (Hg) and levels of methylmercury (MeHg) in fish. Although it is widely hypothesized that increased Hg load to aquatic ecosystems leads to increases in MeHg in fish, there is limited quantitative data to test this hypothesis. Here we examine the available evidence from a range of sources: studies of ecosystems contaminated by industrial discharges, observations of fish MeHg responses to changes in atmospheric load, studies over space and environmental gradients, and experimental manipulations. A summary of the current understanding of the main processes involved in the transport and transformation from Hg load to MeHg in fish is provided. The role of Hg loading is discussed in context with other factors affecting Hg cycling and bioaccumulation in relation to timing and magnitude of response in fish MeHg. The main conclusion drawn is that changes in Hg loading (increase or decrease) will yield a response in fish MeHg but that the timing and magnitude of the response will vary depending of ecosystem-specific variables and the form of the Hg loaded.

Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition

“…We do not know yet whether there will be a proportional response to the continuing increased loading to the lake in the longer term, as suggested by some regional studies (6). For example, if mercury demethylation switched on at some increased concentration of sediment methylmercury, the end response would not be directly proportional to the increase in inorganic mercury loading.…”

“…This issue has now approached a critical juncture because many nations (e.g., the United States and Canada) and organizations (e.g., United Nations Environment Program) are debating the implementation and extent of mercury emission controls. One of the reasons for this debate is that it has been notoriously difficult to establish how annual and regional patterns of mercury loading via deposition influence fish methylmercury concentrations (6). This is because the effects of mercury deposition alone are obscured by various factors [including climate change (7), lake acidification (8), and land use (9)(10)(11)] that act synergistically to influence fish methylmercury concentrations.…”

Polar firn air reveals large-scale impact of anthropogenic mercury emissions during the 1970s

“…Divalent Hg species are subject to rapid wet and dry deposition in terrestrial ecosystems. Some of the Hg 2ϩ deposited in aquatic systems and sediments is transformed into organic methylmercury (5). Although inorganic Hg species have severe health effects on humans, methylmercury is thought to be the highly toxic species involved in bioaccumulation in aquatic food chains.…”

Socio-economic costs of continuing the status-quo of mercury pollution

“…Bacteria in aquatic systems convert a small proportion of the deposited Hg to MeHg, which bioaccumulates in fish (inorganic Hg does not bioaccumulate). Aquatic systems vary in the efficiency with which atmospherically deposited Hg is transformed to MeHg and bioaccumulate in fish (Munthe et al, 2007). For example, the Hg concentration of fish in neighbouring lakes can vary by as much as 10-fold, even when atmospheric Hg levels are similar (Wiener et al, 2006)).…”

“…For example, the Hg concentration of fish in neighbouring lakes can vary by as much as 10-fold, even when atmospheric Hg levels are similar (Wiener et al, 2006)). Nevertheless, in a given aquatic system, the production of MeHg is believed to be approximately proportional to atmospheric Hg deposition (but with variable response time and magnitude), so it is likely that historical increases in Hg emissions have increased MeHg concentrations in fish (Munthe et al, 2007).…”