Chronic sublethal effects associated with branched alkylbenzenes bioaccumulated by mussels
Crude oils are complex mixtures of many thousands of compounds, both resolved and unresolved by conventional gas chromatography (GC). Recent research using comprehensive two-dimensional gas chromatography–time-of-flight–mass-spectrometry (GC × GC-ToF-MS) identified branched alkylbenzenes (BABs) as a major component of some unresolved complex mixtures of hydrocarbons (UCMs) bioaccumulated in the tissues of North Sea mussels, Mytilus edulis, previously found to have poor health status. Here the effect of long-term exposure to low aqueous concentration of BABs and mussels' ability to recover, was determined. Mussels were exposed to 5 μg/L of a complex mixture of C12–14 BABs for 14 d. Feeding rates and the viability of hemocytes were measured immediately after exposure and again after 5 d depuration. Tissues were extracted, analyzed and alkylbenzenes quantified by both GC-MS and GC × GC-ToF-MS. Mussel extracts from previous acute tests were also reanalyzed and quantified using GC × GC-ToF-MS. Mussels exposed to 5 μg/L BABs for 14 d accumulated 46 to 47 μg/g dry weight alkylbenzenes; this was similar to tissue concentrations of mussels exposed to 41 μg/L for 72 h. Feeding rates were significantly reduced (p ≤ 0.05) and were dependent upon tissue concentration. Cellular viability was not significantly affected. Following 5 d in clean seawater, the BABs were only partially depurated and feeding rates failed to fully recover. The use of GC × GC-ToF-MS in the present study has shown that mussel tissue concentrations of complex mixtures of alkylbenzenes, and their corresponding effects, are consistent with reported concentrations within UCM-contaminated wild mussel populations with poor health status.