Petroleum hydrocarbon concentrations in Baltic Sea subsurface water

Many oil hydrocarbons are thought to be a source of toxicity in the marine environment. The Baltic Sea, one of the largest bodies of brackish water in the world, has numerous point sources for oil pollution. In particular, growing maritime traffic, including oil transportation, and several oil harbours have increased the risk of oil-spills. Between 1992 and 2003, the total hydrocarbon concentrations (THCs) of Baltic subsurface water were determined by fluorescence spectroscopy (UVF). Concentrations ranged from 0.13 to 1.8 ug l–1 as Ekofisk crude oil equivalents. To assure comparability of the results, the values were converted to chrysene equivalents (0.010–0.14 ug l–1). Seasonal dependence of the THCs was evident — the lowest concentration was found during summer in the Bothnian Sea and Bothnian Bay and the highest during winter in the northern Baltic Proper. THCs differed geographically following the amounts of oil discharges, with highest values in the Gulf of Finland, the northern Baltic Proper and the eastern Gotland Basin.