Mercury speciation in surface waters of the north sea

Mercury speciation was determined in samples of surface waters of the North Sea. Seventeen stations were visited including coastal waters off the Thames, Humber, Scheldt, Rhine, Ems, Weser and Elbe estuaries. Mercury concentrations measured in the present study are significantly lower than previous estimates for the North Sea, but they are similar to concentrations recently determined in other coastal environments. Concentrations of total dissolved mercury ranged from 0.9 to 4.8 pM with 0.4 to 1.8 pM as dissolved reactive mercury, representing on average about 30% of the total dissolved mercury. Particulate mercury constituted between 13 and 82% of the total mercury (dissolved and particulate) depending on the distribution of suspended particulate matter, with the highest proportions found near the coasts in the southern North Sea. The mercury content of the seawater particles varied between 116 and 484 ng·g⁻¹ with 6% on average as particulate monomethylmercury. A longitudinal profile was completed in the outer estuary of the Elbe river; mercury concentrations reached 16.4 pM for dissolved mercury and 595 pM for particulate mercury in the low salinity region, indicating that the Elbe estuary is contaminated with mercury. This is similar to the contamination measured recently in the Scheldt estuary. The net input of mercury from the Elbe river to the North Sea was estimated at 0.43 kmol·a⁻¹ for dissolved mercury and 4.24 kmol·a⁻¹ for particulate mercury. The mercury concentrations measured in the Elbe estuary are used to estimate the total mercury input from freshwaters to the North Sea. It is comparable to direct atmospheric inputs to the North Sea.