Analysis of sediments from Shetland Island voes for polycyclic aromatic hydrocarbons, steranes and triterpanes

A few days after the grounding of the oil tanker Braer on 5 January 1993, a n Exclusion Zone was designated by Order under the Food and Environment Pro tection Act 1985, prohibiting the harvesting of farmed or wild shellfish wi thin the Zone to prevent contaminated products reaching the market place. T he order was progressively lifted for species that were found to be free of petrogenic taint and for which the polycyclic aromatic hydrocarbon (PAH) l evels were within the range for reference samples. This Order, however, sti ll remains in place for mussels (Mytilus edulis) as the PAH levels are high er than in reference mussels. To investigate the possible source of PAHs fo und in these mussels, sediments were collected from three reference and thr ee Zone sites and their hydrocarbon compositions studied using the n-alkane composition and concentration, PAH composition and concentration and the s terane and triterpane composition. The reference site at Olna Firth was fou nd to have the highest levels of 2-6-ring parent and branched PAHs, the hig hest concentration in one of the pooled sediments being 4530 ng g(-1) dry w eight. Values in the other two reference sites (Vaila Sound and Mangaster V oe) ranged from 248.7 to 902.2 ng g(-1) dry weight. PAH concentrations at t he Zone sites (Sandsound Voe, Stromness Voe and Punds Voe) ranged from 641. 0 to 2766 ng g(-1) dry weight. The PAH data were normalised to the percenta ge of organic carbon and log-transformed prior to being analysed using prin cipal component analysis. The mean total PAH concentrations for Zone sites were found not to be significantly different from the reference sites. The PAH concentration ratios were consistent with the main source of PAHs being pyrolysis. However, there was a petrogenic contribution, suggested by the presence of alkylated PAHs, with Punds Voe having the largest petrogenic hy drocarbon content. This was supported by the triterpane profiles and the pr esence of a UCM in the aliphatic chromatograms from Punds Voe sediments.