The Braer oil spill—Hydrocarbon concentrations in intertidal organisms

The concentrations of non-specific narcotic toxins such as the aromatic hydrocarbons toluene, naphthalene and phenanthrene were determined in specimens of limpets (Patella vulgata) and razor shells (Ensis spp.) collected from Shetland at the time of the Braer oil spill (84 000 t of Gullfaks production crude) and 3, 6 and 15 months after the spill. The analytical methods involved the use of deuterated analogues of the toxins to account for losses of analytes during recovery by steam distillation and determination by cryogenic GC-MS selected ion monitoring of molecular ions. Although the organisms were impacted by oil, the concentrations of total determinants in dead razor shells collected just after the oil spill were below the tissue effective concentrations for 50% reduction in filtering activity (TEC50) for mussels (the most valid toxicological data available for comparative purposes). A portion of the unresolved monoaromatic hydrocarbons of Gullfaks crude would probably add to the burden of toxins, but this was not measured in this study. The distribution of aromatic hydrocarbons in the organisms (phenanthrenes > naphthalenes > toluene) was the reverse of that in the oil and correlates with the expected bioconcentration behaviour of hydrophobic organics whereby less water soluble compounds with higher octanol-water partition coefficients are concentrated. Concentrations of naphthalene to methylphenanthrenes in limpets collected in January at the time of the spill from sites close to the wreck were well below the TEC50 values for mussels but comparison with the lower concentrations in limpets from a more remote site in Shetland indicated that the oil had impacted organisms near to the spill, consistent with intertidal survey data. Comparison with limited literature data for limpets and more extensive data for mussels also supported this conclusion, as did the identification of the oil residues in the limpets by biomarker fingerprinting. As with the razor shells, bioconcentration of the more hydrophobic compounds was observed. Concentrations in Shetland limpets generally decreased with increasing distance from the spill site. Concentrations of aromatic hydrocarbons decreased with time after the spill, such that by July concentrations were at what can reasonably be assumed to be background levels, comparable to the concentrations found at all times in the more remote site. Concentrations in a limited number of samples collected 15 months after the spill, following a further winter of storms in which sediment-sorbed oil could have been reintroduced to the limpets, showed no increase.