Mercury fractionation in sediments of the Lower Vistula River (Poland)

The Vistula is the second largest river in the Baltic Sea catchment area and provides one of the main inputs to the Baltic. The river and its tributaries flow through some of the major industrialized and urbanised regions of Poland, making it one of the most highly human-impacted rivers in Europe. Although the river status is monitored routinely, little is known about mercury forms in the sediments. This study examines mercury fractionation in the sediments of the lower part of the Vistula River. The results show that the cities along this stretch of river have a relatively low impact on both the mercury forms found in the sediment and its bioavailability in the floodplain soils. The mean concentration of total mercury in the sediments was 65 ± 14 ng g-1 dry mass (range 54-92), calculated as the sum of mercury concentrations in the individual fractions. The most abundantly represented of these fractions were mercury bound to sulphides (68 ± 11%, range 55-82%) and humic matter (19 ± 10%, range 10-35%), with lower fractions of water-soluble mercury (6.9 ± 2.9%, range 5.1-13%) and organomercury compounds (6.4 ± 5.3%, range 0.6-13%). The least abundant fraction observed was acid-soluble mercury (0.3 ± 0.2%, range 0.1-0.6%). Similar concentrations and fractionation were observed in floodplain soils from Kiezmark, collected 1, 10 and 50 meters from the riverbed.