EQSs are only applicable in the water column and there are no equivalent standards for sediments used in the UK. Some operational standards for toxic substances may be used in specific circumstances by the environment agencies.

The approach to the development of sediment quality standards has been summarised by Grimwood and Dixon (1997) in the context of List II metals. The Canadian/US approach is recommended and involves the derivation of Threshold Effects Levels (TELs) and Probable Effect Levels (PELs) from an extensive database containing direct measurements of toxicity of contaminated sediments to a range of aquatic organisms exposed in laboratory tests and under field conditions. Effects may be observed in some sensitive species exposed to the TEL, whereas the PEL is likely to cause adverse effects in a wider range of organisms. Further information on the approach is given in Long et al (1995). Interim sediment quality guidelines have been adopted by Environment Canada for a range of toxic substances (CCME 1999). The table linked below summarises some adopted sediment guidelines for List II metals in the Netherlands and Canada.

The table linked below summarises interim marine sediment quality guidelines issued by Environment Canada in 1999 for a range of toxic substances. Grimwood and Dixon (1997) stress that these guidelines have not been validated for use in the UK and that a proportion of the test species in the database are not indigenous to the UK and that there may be fundamental differences in sediment geochemistry. However, in the absence of any UK standards, these guidelines can be used as a first approximation in assessing whether organisms are at risk from sediment concentrations of toxic substances.

There are certain situations where the background concentrations of toxic substances are higher than normal due to human activities over many years but where the indigenous fauna and flora have successfully adapted to these changed conditions. For example, metal concentrations in the Fal estuary system are elevated due to mining activity in the catchment and organisms have adapted to these conditions.

In general, where sediment concentrations of toxic substances are close to or above the TEL concentration listed in the table linked below, conservation agency staff should identify sediment concentrations as a cause for concern and seek to minimise further inputs of these substances to the European marine site.

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