PAH biomonitoring in marine coastal environments

Mediterranean coasts are widely affected by urban (tourism, transport), agricultural and industrial activities, which are responsible for sea contamination by inorganic and organic pollutants. Among them, polycyclic aromatic hydrocarbons (PAHs) are persistent and potentially genotoxic and carcinogenic pollutants, deriving from the incomplete combustion of organic matter (e.g. coal, wood), or from crude oil and petroleum products (e.g. kerosene, gasoline, diesel, lubricating oil). PAHs tend not only to accumulate in sediments and in biological tissues, but also to be magnified along the food chains (Castro-Jiménez et al., 2021). Several studies have highlighted the usefulness of Posidonia oceanica, the dominant endemic seagrass in the Mediterranean Sea, as biomonitor of potentially toxic elements and organic pollutants (Pergent et al., 2011). This species is customarily used as a ‘biological quality element’ in monitoring programs of the EU Water Framework Directive, providing information about the ecological status of coastal ecosystems. The regression of P. oceanica meadows, however, imposes the need to protect this macrophyte and find alternative marine species as passive and/or active biomonitors. In order to identify new potential marine biomonitors of organic pollutants, we compared the concentrations of 14 PAHs in leaves of P. oceanica with those measured in thalli of the red alga Laurencia microcladia, another native macrophyte widespread along the Mediterranean coasts, and in sediments. Both the species were collected from the eulittoral and upper infralittoral zone of the Cilento coast (southern Italy), in 4 sites differing in anthropogenic pressure. On pulverized samples, PAHs were extracted using Matrix Solid Phase Dispersion and sonication from macrophytes and sediments, respectively, and were quantified by GC-MS/MS. The total PAH concentration ranges were comparable between the two species (1.29-1.36 ng/g d.w. for L. microcladia, 1.13-1.35 ng/g d.w. for P. oceanica), but differences could be observed in the accumulation of different PAHs. In particular, benzo[a]pyrene, fluorene, acenaphthene and acenaphthylene were preferentially accumulated in the alga, whereas benzo[b,j,k]fluoranthene, fluoranthene, anthracene, dibenzo[a,h]anthracene in the plant. The comparison with PAH concentrations in sediments indicated that not only for the alga, but also for the plant, the absorption from sediments was negligible. Regardless of the species, the site 5, corresponding to the harbour of San Marco di Castellabate, with moderate (300 moorings) ship traffics, showed the highest concentrations of anthracene and benzo[a]pyrene, in respect to the others sites, subjected to different levels of restrictions (from full to partial reserve) within a marine protected area (Santa Maria di Castellabate). Differences in the accumulation patterns of several PAHs among sites in relation to the level of protection were also observed. Overall, the findings suggest the suitability of L. microcladia in PAH biomonitoring studies, especially in relation to anthracene and benzo[a]pyrene, overcoming the limitations associated to the use of P. oceanica and enabling active biomonitoring campaigns in addition to passive biomonitoring studies. Even in association with analyses on P. oceanica, L. microcladia can still prove useful in improving the accuracy and reliability of results, considering the specific accumulation capability of the two species.