Sulfur organic compounds in bottom sediments of the eastern Gulf of Finland

Abstract

Background, Aims and Scope Despite the large number of studies on the forms of sulfur in marine deposits, investigations on sulfur organic compounds are still rare. It is known that the processes leading to formation of intermediate and final sulfur compounds (including organic ones) in modern deposits are the results of microbiological transformation of sulfur containing proteins, as well as the microbiological reduction of sulfate ions. The latter are finally reduced by anaerobic sulfate-reducing bacteria to H2S, HS− and S2−; the total sum of these is referred to as ‘hydrogen sulfide’ in chemical oceanography. Further, the formation of reduced sulfur organic derivatives (sulfides and polysulfides) is the result of interaction of the organic substance destruction products with the sulfide ions. In such cases, the main source of organic substances, as well as sulfates for the sulfur reducing processes, is the pore water in the sediments. The choice of the target of our study is based on the fact that the eastern part of the Gulf of Finland water area receives the bulk of the anthropogenic load of the St. Petersburg region. Low vertical intermixing of the water thickness is observed there (thus creating a deficiency of oxygen near the bottom), and the bottom sea current transfers the polluted salty water of the Baltic Sea into the Neva Bay. The whole of the above are the preconditions for the formation of sulfur-bearing organic compounds. A great number of bottom sediment samples for analytical surveys were collected in the Eastern Gulf of Finland during research expeditions in the years of 1997 and 2001. These were screened for structures of sulfur organic microcontaminants, including organic forms of sulfur, using advanced instrumentation and experienced personnel in our two, cooperating laboratories. This work is a part of the research being carried out on organic micro-admixtures present in bottom sediments, and is the summary of our findings on previously unstudied sulfur organic substances there.