Surface Sea Water and Sediments

In spite of the importance of the ocean as a source or sink for many halogenated hydrocarbons, there are surprisingly few data reported on occurrence in surface water, and less in the deep oceans. Early work suffered from an inability to completely separate and identify all compounds, particularly those of low molecular weight. Representative figures are shown in Table 5, including some for inshore sediments in an area contaminated by waste discharges. 

As in the atmosphere, vinyl chloride, methylene chloride and ethylene dichloride are not detected, even in inshore water. Waters from an area known to contain industrial effluents contained traces of tetrachloroethane, pen-tachloroethane, and pentachlorobutadiene but even in areas where propylene oxide wastes are discharged, propylene dichloride is rarely found [43, 44]. 

The occurrence of halogenated compounds in rain and snow is poorly documented, but broadly parallels their distribution in the atmosphere [43, 51] concen- 

There is by contrast a very large number of observations of distribution in surface and underground waters, in Germany, Sweden, Switzerland, UK and USA in many cases, where such waters are used as a source for potable water supply, there are parallel observations on the finished drinking water after treatment [1, 7, 21, 30, 33, 43, 49, 51, 52] these also are summarised in Table 6. 

The general impression is of a widespread distribution, at the pg/1 level, of chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene and methyl chloroform methyl chloride, vinyl chloride and ethylene dichloride are virtually absent, despite the large quantity of each known to be produced while methylene chloride is reported locally, and such compounds as hexachlorobutadiene at very low levels only in waters known to be affected by production effluents. There is, nevertheless, a very wide variation about these typical values, of at least 3 orders of magnitude it is difficult, therefore, to quote fully representative levels. Surface waters provide a much lower potential for widespread mixing than does the atmosphere, where concentrations of constituents are much more consistent. Many surface waters also contain the 3 brominated THMs these are probably derived from discharges of chlorinated potable water after use. 

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