A fundamental problem in ecotoxicology is the prediction of long term population and ecosystem-level effects of contaminant exposure based on dose response data of few individuals obtained over a short time period. In addition, environmental fluctuations will always affect significantly the population/ecosystem resilience. However, these fluctuations are not taken into account under dose-response experiments on individuals.
In the Thresholds project we have analyzed some of these questions by using experiments, data analysis tools and modelling approaches. Several important finding may be summarized as follows:
1 Molecular level effects are detected even at concentrations that did not affect the macroscopic end point studied, i.e. growth rate.
2 Natural populations are more sensitive that populations in cultures.
3 There are differences for the same species at different environments, e.g. Mediterranean, Black Seas and Atlantic Ocean.
4 The environmental conditions and the time of release of the contaminant cause a variability of the response at ecosystem level that can reach 50%.
5 At the actual level of knowledge it is difficult to assess if the legal approach, based on the precautionary principle, is over or under conservative, when considering molecular and its long term effects, the combined effects of mixtures and the environmental fluctuations that affect all ecosystems.
6 A similar colour code to the one adopted for biological quality elements should be adopted for the definition of EQS, with values higher than the EQS as orange (poor). This will allow assessing contamination trends and an early detection of a chemical contamination problems.
7 In aquatic environments ecosystem experience the combined effects of mixtures. Ecotoxicological risk assessment should be performed taking this aspect into account. However, with the amount of new chemicals being produced and the detection limits required it is clear that new integrated indicators are necessary. Limiting the levels of certain chemicals in the environment is one step to improve ecosystem health but alone it will not prevent further deterioration.
8 Due to practical limitations, knowledge on ecotoxicology is only available for a small fraction of the anthropogenic chemical pressure. The importance of this simplification has not been comprehensibly assessed and introduce uncertainty in the appropriate outcome of current legislation and managing practices.JRC.H.5-Rural, water and ecosystem resource
