The distribution of heavy metals and arsenic in recent sediments in the Gulf of Finland

A large number of sediment samples representing most of the active mud accumulation areas of the Gulf of Finland were studied for total cadmium, chromium, lead, mercury, arsenic, copper and zinc. The highest concentrations of metals were found in sediment surfaces in the easternmost part of the Gulf, which is influenced by the inflow of the Neva river and the loads of the city of St. Petersburg. Vyborg Bay and the Kymi River also clearly affect the off-shore sea bottom. The vertical distributions determined in four sediment cores show for all metals overall decreasing concentrations towards the surface of the sediment cores, which in part indicates decreased load of metals. Evidently levels of copper, lead and mercury are still decreasing, while cadmium and arsenic levels are slowly increasing in the eastern Gulf of Finland. From the mean sedimentation rate of wet suspended particulate matter (SPM) and dry weight of the surficial sediment, an annual accumulation of 8.7 ¥ 10 t a of SPM was estimated for the Gulf. With that estimate the annual total accumulation of elements into the sediments was calculated. The annual accumulations of cadmium and lead are clearly higher in the Gulf of Finland than in the Gulf of Bothnia. Accumulation of the other metals is somewhat higher in the Gulf of Finland, while the accumulation of arsenic is clearly lower, only one fifth of that in the Gulf of Bothnia.