Mercury in water, porewaters, sediments and fish from the Medway Estuary, Southeast England
This research aimed to investigate the distribution, mobility and potential bioavailability of mercury in the Medway Estuary, Kent, UK, and the impact of feeding regimes on mercury concentrations in the food web, as well as the importance of liver as a storage organ for mercury within fish. Surficial sediment mercury concentrations were typical of an industrialised estuary, ranging between 18-1302 µg kg-1 (dry weight). Three sediment hotspots contained mercury concentrations which are likely to cause adverse affects to organisms. Porewater mercury concentrations ranged between <0.01-1.75 µg L-1, and were not correlated with mercury in the solid phase. The lowest partition ratio between mercury concentrations in sediment and porewaters was observed at four locations in the mid-stream and towards the mouth of the estuary (log Kd = <2). At these locations a greater fraction of total sediment mercury (sediment plus porewater) is likely to remobilise and potentially become more bioavailable. Mercury porewater concentrations are elevated in comparison with overlying waters, suggesting a diffusive release of mercury from the bottom sediments to the water column. The calculated diffusive flux was 6 kg year-1, demonstrating that mercury is mobile in this system. Mercury in sediment core samples ranged between 382-1888 µg kg-1 (dry weight). Dredging the Medway would release mercury from these more contaminated deeper sediments into overlying water, thus having potentially ecotoxic consequences. Within the cores, methylmercury concentrations ranged between 0.3-0.8 µg kg-1 (dry weight) and organomercury ranged between 2-48 µg kg-1 (dry weight). Mercury concentrations in fish flesh ranged between 0.01-0.63 mg kg-1 (wet weight), with all specimens being within the EU limit for human consumption.