The pattern of spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in seawater, sediment, and mussels, potential toxicity of different matrices, and mussel anoxic survival from six sampling sites of the Gulf of Rijeka, the Adriatic Sea, Croatia was examined. The total concentrations of 10 PAHs vary from below detection limit to 305 ng/L in seawater, from 213 to 695 microg/kg dry weight in sediment and from 49.2 to 134 ng/g wet weight in mussel tissue. Combustion is the principal source of PAH contamination in seawater and sediment samples. Sediment samples are distinguished from the majority of seawater and mussel samples by the presence of high molecular weight PAHs, whereas mussels from majority of sampling sites tend to accumulate PAHs of lower molecular weight. The PAH dynamic between different matrices is complex and site specific. Toxicity of seawater and sediment organic extract is correlated with PAH content, indicating that PAHs are the predominant toxic compounds. There is no correlation between toxicity of mussel biological fluids and toxicity of seawater and sediment, or between toxicity of mussel biological fluid and PAH content in mussel, seawater, or sediment. There is a positive correlation between potential toxicity of mussel biological fluids and reduction of anoxic survival time. Mussel anoxic survival is influenced by the presence of complex mixture of toxic contaminants, not only PAHs. The relationship between PAH contents in different marine matrices and their ability to affect mussels revealed specific interactions between an organism and complex mixture of toxic contaminants present in the marine environment.

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The aim of this study was to compare the capability of "passive" and "active" biomonitoring to determine the environmental pressure. For this purpose, PAHs content and several biological responses in resident and caged mussels (Mytilus galloprovincialis) at five sampling sites (Rijeka Bay, Adriatic Sea) were analsed. Resident mussels were found better in reflecting the level of PAH loads at particular sites while only caged mussels could detect input of HMW PAHs. When data of each investigated parameter were compared separately, the majority of differences between resident and caged mussels' results were site-specific. Integration of biological response patterns expressed as Index of Biological Response (IBR) resulted with different sampling sites ranking for resident and caged mussels. Multiple Factor Analysis (MFA) based on integration of tissue PAH concentration and biological response revealed resident mussels as more powerful for detection of environmental pressure. The use of resident mussels is recommended as appropriate and less costly approach for monitoring the effect of pollution.