| Results |
In order to increase the ecological relevance of intersex (ISI) in periwinkle (Littorina littorea) as a biomarker for TBT pollution , this study investigates the relationship ISI values between 1998 and 2005 predicted by a theoretical risk assessment model and ISI values actually observed in a field study. The study was based on ISI and risk percentage predictions made on the basis of the spatial distribution of tributyltin (TBT) concentrations in sediments and in suspended matter (SPM) and on the experimentally determined prevalence of ISI in periwinkles.
The objective of this study was to validate the risk assessment in the field, in order to reveal the actual field status. As the results obtained provided insight in the relationship between TBT concentrations in different compartments of the environment and imposex/intersex effects, and validate the use of ISI as an ecological biomarker for TBT pollution that may complement chemical analyses. Concentrations of TBT in Dutch coastal waters and harbours have been obtained from extensive field studies conducted between 1998 and 2003. Levels of TBT measured in water, SPM, sediment and dredged material ranged from 0.5 to 5700 µg Sn.kg-1 dw.
A probabilistic risk assessment was performed on the basis of our chemical data. The ecological risk calculated for open waters ranged from 4.2% of species predicted to be affected to 15.3%; for harbours it ranged from 3.5% to 26.9%. Concentration distributions were also used to predict ISI values in periwinkles based on the dose-effect curve for intersex effects derived from the literature.
The results of our study showed that an ecological risk value of up to 10% can exist in open waters and harbour areas while the predicted ISI levels remain within the natural ranges. In water systems where the ISI signalling level of 0.7 is predicted to be exceeded, the ecological risk was found to be higher than 10%. In addition to these predictions of ISI values on the basis of chemical TBT data, ISI values were also experimentally determined in harbour areas and open waters. Almost all ISI levels measured in the field (higher than natural background levels) fell within the ranges of predicted ISI levels.
It can be concluded that spatial distributions of TBT concentrations reflect the effective TBT concentrations. It was shown that although relatively low sensitivity and slow response may somewhat hamper the use of ISI in Littorina littorea as an early warning indicator of ecosystem health, the specificity of the response renders it a suitable indicator of TBT exposure. Therefore, in harbours the relationship between ISI and high levels of TBT contamination, shows a risk to organisms. The ecological risk of exposure to very high concentrations TBT for gastropods is discussed in this study, suggests TBT compounds should be integrated when assessing the risk of hazardous substances on health and viability of organisms inhabiting Dutch waters. |