This project will analyse methylmercury concentrations within known trophic pathways to i) better establish the risk associated with eating seafood, ii) explain the disparity between environmental and biotic mercury levels and iii) determine the methylmercury contribution to varying trophic levels and thus clarify the relationship between total mercury loadings and bioaccumulation potential.
Human mercury exposure is primarily due to consumption of seafood (Chen et al. 2009), with young children and pregnant women most at risk.
The Derwent estuary is highly contaminated with mercury; with fish levels consistently exceeding FSANZ maximum permitted levels (0.5 mg kg-1). However, the literature is divided as to the source of mercury accumulation in fish; some studies suggest a strong influence from the surrounding water and sediments (Blevins and Pancorbo, 1986; Calta and Canpolat, 2006, Kehrig et al., 2010) whilst other studies suggest environmental levels are a poor indicator (Langlois et al., 1987, Verdouw et al., 2010) and that contamination arises through specific mercury bioaccumulation pathways.
Mercury accumulates in marine food webs as the organic form, methylmercury, which is particularly toxic, persistent and readily biomagnifies (Chen et al., 2009, Ward et al., 2010). Sediment mercury is largely inorganic and, depending on environmental conditions, frequently biologically unavailable (Chen et al., 2009). An important step in determining trophic accumulation and toxicity potential (“mercury budget”) is to establish the methylmercury component at each trophic level. Despite evidence that methylmercury percentages increase with trophic level (Kehrig et al., 2009; Kasper et al., 2009), there is no accurate way of predicting this component without direct measurement (Chen et al., 2008). This project proposes to analyse and document the methylmercury contributions to each of the key fish species listed and describe the influence of life-history, feeding preference, trophic level, and spatial and temporal differences on fish loadings.
Final report
Estuarine systems that are exposed to industrial pollutants often retain a high loading of contaminants, including mercury (Hg), due to prevailing physical, chemical and biological conditions. Estuarine biota are principally exposed to Hg through dietary uptake, which can lead to higher order species bioaccumulating significant concentrations that can also be harmful to human health if consumed. Methylmercury (MeHg) production, bioaccumulation, and biomagnification in estuarine food webs are broadly understood but our knowledge of Hg food pathways and selenium’s (Se) interaction with Hg is lacking. Current observations show poor correlation between bioaccumulation and environmental loadings, indicating that food web uptake and transfer of Hg are not straightforward. Understanding the mechanisms that underpin this variability is critical to quantifying and managing Hg exposure risks, and for developing appropriate management actions.
The studies within this thesis examined the bioavailability, trophic magnification and bioaccumulation of Hg within a contaminated estuary to provide better capacity to manage the ecosystem and human health concerns.
