Bioaccumulation of nonylphenols (NPs) and polycyclic aromatic hydrocarbons (PAHs) in Tapes Philippinarum in the Venice Lagoon (Italy)

Biomonitoring is a scientific method for assessing the health status of the environment to natural and synthetic chemicals, based on sampling and analysis of organism's tissues and fluids. This technique relies on the knowledge that chemicals induce markers reflecting this exposure: the marker may be the chemical itself. Different models have been used to study the bioavailability and the bioaccumulation of contaminants: the Biota-Sediment Accumulation Factor (BSAF) predicts that in the organism's tissue the chemical residue can be estimated from the partitioning of the compound between the lipid fraction and the organic carbon in the sediment. In this work the BSAFs of NP and PAH in Tapes philippinarum from the Venice lagoon were calculated, with the aim to verify if the routine biomonitoring studies are reliable in contaminated sites. A field campaign from October 2003 to June 2004 in three sites of the Venice lagoon was realised: Marghera characterised by high contamination levels of industrial origin, Campalto located close to a sewage treatment plant and Poveglia benchmark site, located near one of the lagoon mouth. Results showed that Marghera and Campalto sediments were more contaminated by NPs and PAHs than Poveglia. In each sampling date, the highest NP concentrations (64-247 ng/g d.w.) were measured in Marghera sediments while the lowest one (28-99 ng/g d.w.) in Poveglia. The higher mean concentrations of PAHs were found in Marghera sediments in April and June (516 and 364 ng/g d.w. respectively), while in October and January the higher values were detected in Campalto, with a mean PAH concentration of 821 and 668 ng/g d.w., respectively. Different trends were observed in the contamination of clams: the Poveglia site, in April, showed the highest NP and PAH contamination with values, respectively, of 181 and 1160 ng/g f.w.. From these values, BSAFs were calculated, which resulted always highest at Poveglia for both classes of contaminants. The BSAF trend appears to be inversely related to the contamination level of the sites. Environmental stressors can have an impact on the health status of the clams, altering their normal feeding behavior and, as a probable consequence, reducing the bioaccumulation rates. This could mean that the concentration measured in biota are not necessarily representative of the biota exposure with the risk of losing the direct correlation between sediment and biota concentrations in contaminated sites.