Identification and quantification of 18-nor- and 19-norditerpenes and their chlorinated analogues in samples of sediment and fish

Abstract

The norditerpenes 18-norabieta-8,11,13-triene and 12,14-dichloro-18-norabieta-8,11,13-triene, corresponding to decarboxylation of dehydroabietic acid and 12,14-dichlorodehydroabietic acid, respectively, were isolated from environmental samples of sediment and fish from the Gulf of Bothnia. Identification was unambiguously accomplished by comparison with synthetic reference compounds whose structures were established by NMR. The synthetic product was a mixture of the nor epimers at C-4 in the ratio of ca. 1:3, and NMR showed that the 18-nor epimer was the major component. Whereas the 18-nor epimer was the dominant C 19 hydrocarbon in the sediment samples, the 19-nor compound dominated the C 19 hydrocarbon fraction in the samples of fish. These C 19 terpenes are probably environmental transformation products of the corresponding dehydroabietic acids. The 18-nor hydrocarbon was quantified in sediment samples, which were also analysed for a number of other compounds representative of alicyclic and aliphatic components of bleachery effluents. The 19-nor hydrocarbon was conclusively identified, although not quantified in samples of fish. 12,14-Dichloro-18-norabieta-8,11,13-triene was identified in samples of sediment and fish which also contained the 19-nor compound. The presence of both hydrocarbons in fish was consistent with the experimentally determined estimates of their bioconcentration potential by reversed-phase HPLC. A number of other norabietanes and bisnorabietanes were tentatively identified in both sediment and fish samples, together with their dehydrogenation products, and a hypothetical scheme relating these to dehydroabietic acid is proposed. Attention is directed to the value of procedures including open-column chromatography on silica gel, gel permeation chromatography and mild chemical treatment for preparing and pretreatment of samples before identification. It is emphasized that analytical procedures should be directed to the specific structure of the analyte and will depend on the nature of interfering compounds in the samples. The search for universal methods that are applicable to structurally diverse analytes may be unrealistic.