Estimation of PCDD/F and PCB detoxification rates in contaminated Tapes philippinarum in the Lagoon of Venice.

This work presents the results of a short-term natural detoxification experiment carried out with the contaminated Manila clam (Tapes philippinarum), an edible bivalve species subjected to intense exploitation in the Venice Lagoon. The concentrations of seventeen PCDD/F congeners and twelve dioxin-like PCBs were determined in sediments as well as T. philippinarum specimen sampled in a lagoon area contaminated by industrial pollution. Clam specimen were then transplanted and reared in an area of low contamination. Concentrations of PCDD/Fs and PCBs in clam flesh were determined from samples collected after 10, 20, 30, 45, 60 and 120 days from redeployment. The results show a very rapid decrease of pollutant concentrations towards asymptotic values. Due to rapid decrease, the estimated first-order decay constants were statistically significant (p <or= 0.05), for ten out of 29 congeners, namely: 2,3,7,8-TCDD, 1,2,3,7,8-PCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, 1,2,3,7,8,9-HxCDF, 1,2,3,4,7,8,9-HpCDF, PCB#114, PCB#167, PCB#157 PCB#189. Estimated detoxification half-lives for the five PCDD/F congeners, which accounted for approximately 40% of the Total Toxicity, were very consistent and ranged between 5 and 6 days. Although preliminary, these findings indicate that the redeployment of young clam specimen collected in productive but polluted areas and reared in areas of low contamination may be taken into consideration as a management solution for a safe exploitation of the resource.