EQSs have been derived under the requirements of the Dangerous Substances Directive which classifies substances as List I and List II.

Standards for List I substances have been defined in 'daughter' Directives to the EC Dangerous Substances Directive. The scientific justification for the standards is not available. Standards for List I substances are given in the linked table.

The Dangerous Substances Directive required that standards for List II substances are derived by the member states. The UK has set EQSs for List II substances which have been derived by WRc according to the methodology described in Grimwood and Dixon (1997). For each of the List II substances, reports are available which describe the data used to derive the standards and any uncertainties in the derivation. Where there are uncertainties arising from a lack of information on effects on saltwater organisms, larger safety factors have been used in the derivation of the EQS. The linked table below summarises the EQSs for List II substances and includes information on any uncertainties in the derivation of the standard. In the majority of cases, both an annual average (or annual mean) and a maximum allowable concentration were proposed. However, often only the annual average has been made into a statutory standard.

The environment agencies (i.e. the Environment Agency, SEPA and Environment and Heritage Service, Northern Ireland) have a legal obligation to ensure that statutory EQSs are met. When considering the effect of substances in European marine sites, conservation agency staff should ensure they are aware of the EQS being used, the form of its application (annual average or maximum allowable concentration) and whether uncertainties in the derivation of the EQS have been taken into consideration. Conservation agency staff should refer to the relevant section in Appendices B and C and, if necessary, the additional literature referenced there, before concluding whether an EQS is likely to be adequate for the protection of an SAC or SPA feature. Uncertainties in the applicability of EQSs for the protection of Natura 2000 sites should be drawn to the attention of EA staff during consultation.

Grimwood and Dixon (1997) assessed the adequacy of EQSs for List II metals in relation to the protection of sites of nature conservation interest. Uncertainties arising from this study have been included in the table linked below.

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