Determination of selected organochlorine compounds in seawater

Several man-made organochlorine compounds have become ubiquitous environmental contaminants. Considerable concern about their presence even at extremely low levels in seawater stems from their persistence, solubility in lipid tissue (and thus high bio-concentra-tion and bio-magnification factors) and direct or long-term harmful effects Safe and Hut-zinger, 1987 Kimbrough and Jensen, 1989). Because of their very persistence, distribution patterns in seawater and in suspended particles may also be used to study oceanic processes. 

To understand the mechanisms of distribution, transport, degradation and possible detrimental effects of organic compounds in the marine environment, access to accurate analytical data on well defined compounds is essential. In this chapter attention will thus be focused on the application of high-resolution capillary gas chromatography. 

The distribution of trace organic compounds such as chlorobiphenyls (CBs) and polycyclic aromatic hydrocarbons (PAHs) in seawater and marine particulate matter is determined by the complex influence of physical, biological and chemical processes. The interpretation of horizontal and vertical distribution patterns of these substances requires information on the corresponding characteristics of the water bodies, e.g., temperature, salinity, depth and the concentrations of nutrients and dissolved oxygen. 

The chlorobiphenyls are chemically related compounds with a wide range of physicochemical properties such as vapour pressure, water and lipid solubility, and particle/solution distribution coefficients. They can thus be used as model compounds to forecast the behaviour and distribution of other, less well studied organics. The CB distribution patterns can be used as a basis for theoretical models to evaluate the reliability of experimentally determined distribution patterns of a variety of compounds. 

Experience gained during the last decade in the determination of CBs in off-shore surface and deep waters has shown that concentrations are extremely low, much lower than reported earlier (see Table 22-1). Concentrations reported for the Mediterranean Sea (Tolosa et al, 1997 Schulz-Bull et al., 1997), the North Sea Schulz-Bull et al., 1991) and the Baltic Sea Schulz-Bull et al., 1995) were well above those found in surface waters of the open ocean Iwata et al., 1993 Schulz-Bull et a/.,1998). In deep-ocean water Schulz et al., 1988 Petrick et al, 1996 Schulz-Bull et al, 1998) much lower concentrations were found than in surface waters. In North Atlantic Deep Water, values of individual CBs were found to be 0.01 pg/L, yet concentrations in solution were higher than those in suspended material on an equal volume basis. It turns out that the distribution of CBs between solution and suspension is determined primarily by molecular properties (characterized by octanol/water distribution coefficients). However, biological processes disturb the establishment of equilibria. This phenomenon has been observed in river water, in estuarine and coastal waters and during biologically active periods in the surface layer of the open ocean. 

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