Decalin has a wide range of uses (for example, as an industrial solvent; as a substitute for turpentine in the manufacture of paints and as a motor fuel additive and lubricant). Decalins and alkylated decalins can enter the marine environment via ongoing discharges of oil in produced water and, historically, from discharges of oil based drilling muds from oil and gas platforms. Studies of fish in the North Sea have shown that they are contaminated with these compounds. The aim of this work was to develop the capability to analyse for these determinants and conduct a survey of biota and sediments. A literature review of environmental occurrence, toxicity and analytical methodologies applied to determination of decalins was undertaken initially. Subsequently, a gas chromatography-mass spectrometric (GC-MS) instrumental methodology was optimized for a suite of decalin (cis-/trans- isomers) and alkylated decalin (C1, C3 and C5) standards. The purity of some of the alkylated standards was quite low and their analysis showed that they consisted of several isomers of each compound making their analysis challenging. The instrument limits of quantitation for the decalin compounds ranged from 10 pg.μl-1 to 100 pg.μl-1 and instrumental response was linear over the full range of calibration concentrations.
A method was subsequently developed to extract and cleanup decalins in biota and sediments. Each homogenised sample, whether biota or sediment, was extracted using alkaline saponification followed by liquid/liquid extraction. The sample extract was then passed through an alumina chromatography column in order to remove polar compounds.
The method was fully validated through spiking experiments, quantification being made by means of deuterated internal standards added to samples prior to extraction. The method accuracy and precision was satisfactory for cis-, trans- and C3 decalins in biota samples. However, for sediment, poor recoveries and/or a lack of precision for the whole suite of decalins meant that the sediment method could only be considered as semi-quantitative.
Levels of decalins were subsequently determined in dab (Limanda limanda) muscle and sediments samples collected in 2005 under the Clean and Safe Seas Environment Monitoring Programme (CSEMP) from sites around England and Wales and in a small number of mussels (Mytilus edulis) from the Ribble area. Decalins were only detected in 3 dab muscle samples (out of 24), at relatively low levels. In contrast, 2 out of 3 mussel samples contained at least 2 different decalins. All sediment samples (n=6) analysed were contaminated with decalins, with cis-/trans- isomers being detected in all samples. C1 decalin was detected in exactly half the samples analysed, all collected off the North East coast of England (off Tees and off Wash sampling sites). The high occurrence of decalins in a small number of mussel and sediment samples, substantiate further method development to improve the accuracy, precision and repeatability of the sediment methodology and a wider survey of the UK marine environment so as to improve the understanding and assessment of decalin contamination in the UK marine environment.
