Mercury and Methylmercury in Southern Baltic Sea Sediments

Surficial sediment samples were collected in several areas of the southern Baltic Sea during cruises of R/V Oceania in spring 2009 and 2010 for all stations and in autumn 2009 for Gdansk Deep and Gotland Deep. Samples were collected with a gravity corer. The top five centimeters of sediment were sampled by cutting it away with a plastic spatula, mixed and stored frozen (-20C) in polyethylene bags until analyses in the laboratory. Sediment cores were analysed for total mercury [HgTOT]and methylmercury [MeHg]. Total Hg concentrations in sediments were between 5,81 ng·g in Odra Eustary and 225 ng·g in Gdansk Deep. Lowest concentration of methylmercury were recorded in Odra Estuary; 61,29 pg·g. Highest concentration of MeHg were found in Vistula Estuary, 940,07 pg·g.


Introduction
Environmental contamination by mercury is a worldwide problem.It is important to assess the possible effects of increasing levels of environmental mercury pollution on human health and the environment (Liao et al., 2006).Mercury (Hg) is a potent toxic substance, the toxicity of which is elicited at very low concentrations.Although all chemical forms of mercury are toxic, public health concerns are focused on methylmercury (MeHg).Methylmercury is a neurotoxin that causes pathologies ranging from mild numbness of the extremities to blindness, loss of balance, and in severe cases, death (Barkay and Wagner-Dobler, 2005).In the marine environment mercury, owing to its affinity for particulate matter, is readily scavenged from the water column (Laurier et al., 2003) and transferred to bottom sediments (Cossa and Gobeil, 2000).
The aim of this study was to demonstrate levels of total mercury and methylmercury concentrations measurements in sediment samples collected in southern Baltic Sea.Before analysis all the sediment samples were freeze-drying and homogenized.Total mercury determination were performed via pyrolysis where the trap is heated in a stream of oxygen (Leco AMA 254).The AMA254 technique of direct combustion features a combustion/catalyst tube that decomposes the sample in an oxygen-rich environment and removes interfering elements.A gold amalgamator trap collects all mercury from the evolved gases and a dual-path length cuvette/spectrophotomer specifically determines mercury over a wide dynamic range.

Surficial
For methylmercury the following procedure for sample preparation and extraction was used (Quevauviller et al., 2000;Logar et al., 2000;Liang et al., 1994).Methyl mercury defined by this procedure includes all monomethyl mercury forms and species found in sediments (e.g.CH3Hg+, CH3HgCl, CH3HgOH, and CH3HgS-R), which are amenable to complexation and extraction as CH3HgBr.The use of the pre-extraction procedure eliminates any interference from organic matter, particulate, and sulphides, and strongly reduces the positive analytical artefact generated by the interaction of ambient inorganic mercury with organic compounds (especially humics) in the samples (Hintelmann,1999).To wet sediment were sequentially added a 1.5M HBr solution and 1M CuSO4.When the effervescence ceased, MMHg was extracted into CH2Cl2.Organic phase was collected into a teflon vial containing E3S Web of Conferences 20 ml of Milli-Q water, the vial was heated at 80C and finally purged with N2 until all CH2Cl2 had been volatilised out.After dilution to a known volume with reagent water, analysis was carried out by aqueous phase ethylation.By purging the sample with N2, ethyl methyl-mercury was transferred to a Tenax trap and then analysed by using the GC/pyrolysis/CVAFS technique.

Results and Discussion
Mercury content in surficial sediments from southern Baltic Sea is typical for this kind of seas.(Fig. 1).Very similar situation was reported in Kannan and Falandysz (1996) research.Authors recorded concentrations in coastal marine sediments in the range of 37 -312 (mean 163) ng•g -1 .In comparison with the Mediterranean region, Baltic Sea is only slightly contaminated area.Concentration of total mercury in this region ranged 0,10 -22,30 µg•g -1 (Covelli et al., 2000).
The present study showed also levels of methylmercury concentrations in sediments from southern Baltic Sea.The highest mean value were located in Vistula Estuary in spring 2010 (626,71 pg•g -1 ).Others mean values ranged from 80,63 pg•g -1 (Vistula Estuary, spring 2009) to 375,25 pg•g -1 (Gdansk Deep, spring 2010) (Fig. 2).Previous studies of methylmercury in this area showed similar level of contamination in coastal sediments.Kannan and Falandysz (1996) reported that methylmercury ranged from 35 to 250 pg•g -1 .
Figure 3 presents correlation between total mercury and methylmercury.Positive correlation (coefficient is 0,7549) showed that in southern Baltic Sea sediments conditions are favoring mercury methylation.

Conclusion
Mercury is highly toxic metal, especially methylmercury.Present studies showed that levels of MeHg in sediments are significant.That is the reason why further studies concerning mercury speciation and discharge to the coastal zone are essential.
sediment samples were collected in several areas of the southern Baltic Sea during cruise on the R/V Oceania in spring 2009 and 2010 for all stations and in autumn 2009 for Gdansk Deep and Gotland Deep.Location of the sampling stations are shown in Figure 1.Samples were collected with a gravity corer.The top five centimeters of sediment was sampled by cutting it away with a plastic spatula, mixed and stored frozen (-20 O C) in polyethylene bags until analyses in the laboratory.

Fig. 1 .
Fig. 1.Mean values of total mercury concentrations in southern Baltic Sea sediments.