Nonylphenol in water and sediments from the Lagoon of Venice: first evidence of endocrine disruption in the clam Tapes philippinarum

Nonylphenol (NP) is commonly used in the production of nonylphenol ethoxylates (NPEs), NP phosphites and insecticides. As a consequence of their widespread use, particularly of NPEs as nonionic surfactants in household and industrial detergents, large quantities of these compounds are discharged into aquatic environments, either directly from untreated effluent or indirectly from sewage treatment plants (STPs). In aquatic ecosystems, NPEs biodegrade to de-ethoxylated intermediates, whose final product is NP. It is known that NP can have estrogenic effects in aquatic organisms, being able to mimic the action of endogenous estrogens by binding to estrogen receptors. As a consequence, it can induce vitellogenin (Vg) synthesis, the major precursor of the egg-yolk proteins of oviparous organisms. In this study, Vg induction was evaluated in the clam Tapes philippinarum seasonally collected (from October 2003 to June 2004) in 3 sites of the Lagoon of Venice: Marghera (MA), characterised by high industrial contamination levels, Campalto (CA), nearby a STP, and Poveglia (PO) close to the Lagoon inlet. Vg-like proteins were determined in the haemolymph and digestive gland of sexually differentiated males and females when it was possible to distinguish them by microscopic observation of a smear of gonadal tissue. In the haemolymph Ca2+ levels were also measured, this parameter being strictly related to the presence of Vg-like proteins. During clam samplings, water and sediments were also collected to determine the concentrations of NP, which was chosen as a marker of the presence of anthropic sources of estrogenic compounds. Both male and female clams collected at CA and MA generally showed significantly higher Vg-like proteins in haemolymph with respect to specimens from Poveglia throughout the study period. Significant differences in Vg-like proteins were also detected in digestive gland of clams from the 3 sampling sites. In particular, sexually undifferentiated clams collected at CA showed the highest protein levels in January 2004, suggesting that endocrine alterations mostly occurred far from the reproductive period of animals. Ca2+ levels were generally higher in haemolymph of both female and males clams from CA and MA. Ca2+ levels showed also a clear seasonal trend, with higher values in spring-summer period than in autumn-winter. Among sampling sites, MA and CA showed higher sediment NP concentrations than PO. The highest NP concentrations, ranging from 64 to 253 µg/g d.w., were always detected in sediment from MA, whereas the lowest NP concentrations, ranging from 24 to 97 µg/g d.w., were found in sediment of PO. NP water concentrations were generally close to the analytical detection limit (50 ng/l) at all sampling sites. This study demonstrates that Vg-like protein levels significantly increased in both hemolymph and digestive gland from sexually differentiated and undifferentiated clams from the most NP contaminated sites. Considering that endocrine disruption due to exposure to estrogenic compounds, such as NP, may cause fertility reduction, alteration in sex ratio, and a decrease in reproductive rate, a condition of potential risk for clam populations in estuarine areas is highlighted.