Organochlorine levels in viperine snake Natrix maura carcasses from the Ebro Delta (NE Spain): Sexual and size-related differences

Organochlorine compounds (PCBs, DDTs and HCB) in carcasses from a populatio n of the Viperine Snake (Natrix maura) living in the Ebro Delta were analyz ed. This is a wetland area on the Mediterranean coast when the natural ecos ystem has been partially substituted by rice fields. High levels of polluta nts (mainly DDTs and PCBs) have been detected in several species living in this area, due to the production of these compounds by a former industrial activity upstream as well as agricultural activity in the Delta. Organochlo rines were analyzed in adult males and females, and in immature snakes. DDT s (mainly p,p'-DDE) were the most abundant pollutant present. The DDT/PCB r atio was higher than expected, which is consistent with the position of the Viperine Snake in the trophic web as well as the type of prey consumed. Im mature snakes had more organochlorines than adults. However, the broad rang e of concentrations shown by immature snakes, suggested that part of the or ganochlorine load is transferred from gravid females to their eggs. In adul ts, organochlorine concentrations increased with carcass weight in both mal es and females. This increase was higher in males since females lost contam inants through fat investment during vitellogenesis. Seasonally, PCBs and D DTs levels increased in spring when snakes showed higher feeding activity, whereas higher levels of HCB were present at the end of summer, when the ri ver input increased. Furthermore, HCB does not seem to biomagnify well acro ss the trophic chain. Organochlorine concentrations in Viperine Snake carca sses were high since: 1) the dry tissue had less than 5% of fat, and 2) sna kes were caught many years after the DDT ban, supporting the fact that clea ning of the ecosystem does not occur easily. These results indicate that sn akes are adequate as indicators of the contamination in natural ecosystems but sex and body size of the samples should be taken into account for inter pretation of results. (C) 1999 Elsevier Science Ltd. All rights reserved.