July 8, 2010 by Adam Peters

Many European Environmental Quality Standards (EQS) for chemical toxicants are being revised and updated under the Water Framework Directive (WFD), and some significant changes from previous standards and approaches have been proposed. At wca we have been closely involved in the development of approaches for incorporating bioavailability into some standards for metals, although this is not a new concept as many quality standards for metals in freshwaters have varied depending on water hardness for many years in several regulatory regimes. The integration of different pressures on aquatic ecosystems into a single classification scheme, which recognises that a variety of different types of stressors may result in degradation of aquatic ecosystems, represents a major change for many Member States. Whilst the use of field evidence in EQS derivation has been limited in the past, the WFD recognises the importance of field evidence and suggests that derived standards should be compared against any evidence from field studies in order to refine the assessment factor used in the derivation of the EQS (See WFD See Annex V 1.2.6iii).

In some cases the traditional approach of deriving an EQS from ecotoxicology test data and applying an assessment factor to derive an acceptable level in the environment may be inappropriate, especially in cases where the available test data are uncertain and the observed effects may not necessarily be due to chemical toxicity. The derivation of an EQS for iron may be such a case, and previous UK efforts to derive a PNEC from ecotoxicity test data and an assessment factor resulted in a PNEC which was below ambient background levels in unimpacted areas. There is a large body of field monitoring data in the UK for both ecological quality and water quality, and we have been analysing this to assess the effects of iron on freshwater ecosystems. The approaches employed require a large body of monitoring data, and the identification of effect thresholds requires that there are impacts on the local ecology at some of the sites due to the substance of interest ). The possible standards which we have recently developed for iron for the Environment Agency of England and Wales have the potential to align acceptable levels of iron in the environment with established levels of ecological quality under the WFD. This has never been possible before, and may allow a much greater degree of integration of chemical and ecological criteria for freshwater in the future.