6 mg Pb kg−1, a little lower level than, 85 mg kg−1, presented in literature (Szefer et al., 2009). In the case of zinc, a jump from 88 mg kg−1 to 163 mg kg−1 was defined to take place between 1920 and 1950. Later on, Zn content oscillates around 185 mg kg−1; the literature data point out a quite similar level of 188 mg kg−1 (Szefer et al., 2009).

Enrichment factor is widely applied to differentiate metal sources: anthropogenic and natural origin (Carvalho Gomes et al., 2009 and Zahra et al., 2014). Enrichment factor (EF) is defined as the ratio of the given metal concentration measured in the environment element to the concentration level regarded as the environmental target concentrations. Enhanced values of EF indicate the increased heavy metal concentrations resulting

mainly from anthropogenic pressure. To illustrate the temporal changes of heavy metal concentrations, enrichment factors EF in particular sediment layers Dinaciclib related to background levels from the deepest layer were calculated according to the formula: EF=CMLCMBwhere CML – metal concentration (normalized to 5% Al) in sediment layer x, CMB – metal concentration (normalized to 5% Al) in background layer. As anticipated, the highest EFs were obtained for all four heavy metal species in surface sediments of the Gdańsk Deep (Fig. 5). In Fig. 5, the EF values are presented as calculated as a ratio of metal concentration in each sediment layer – CML to the target concentration of metal – CMT. The highest enrichment factors were obtained for cadmium; Lumacaftor supplier its concentrations measured in 2009 were nearly 13-fold higher than the background level. Lead turned out to be the second pollutant with respect to concentration increase in the surface layer related to the deepest layer with EF >10. Mercury concentrations increased over five times, and zinc showed the least spectacular increment, with the maximal EF of 2.2. The weakest changes in relation to reference conditions were noted in the SE Gotland Clomifene Basin. EF values of Pb and Zn in this region varied within similar ranges, with

a maximal point of 1.5 assigned about 1990. Quite similar EF records, though at a much lower level than that in the Gdańsk Deep, were found here also in the case of Cd with the maximum at 2.9 in the surface layer. In the case of mercury, the maximal EF of 3.0 was found around 1980. In the Bornholm Deep, the build-up of Cd and Hg concentrations in sediment layers were shown to follow approximate patterns as evidenced by the maximal EF of 4.05 and 4.07, respectively, in the surface layer. The maximal EF levels of zinc and lead in the Bornholm Deep were 2.27 and 2.38, respectively. Among the studied marine sedimentation basins, the area of Gdańsk Deep remains under the most severe anthropogenic pressure. The EF increasing >1.0, indicating enhanced input of heavy metals to the marine environment, dates as far back as 1828, while the maximal increment gradient was noted after 1979.