Previous studies have shown a significant variation between national EQS values. The aim of the present study was to investigate possible reasons for the variability observed for some EQS values derived by individual member states regarding rivers. Based on questionnaires targeting 19 selected substances with relatively large EQS variations, the member states provided details on how the national EQSs for these substances had been derived.
A questionnaire was circulated to all EU countries in autumn 2014, to consolidate the data set and to explore the background for EQS derivation. The questionnaire included the national EQS values taken from Irmer et al. (2012; 2014), and the following ten questions:
1. If the value is incorrect, please add the correct value.
2. Which year was the EQS set?
3. Did you use Technical Guidance Document No. 27 for deriving EQS?
4. Did you employ the deterministic (assessment factor, AF) method or species sensitivity distribution (SSD) plus AF method?
5. Did you employ micro- or mesocosm studies and/or field studies?
6. What was the value of the assessment factor used?
7. Which endpoint and value triggered the EQS?
8. What was the reliability index score (e.g. Klimisch) of the trigger value?
9. Please provide the reference for the trigger value.
10. Please provide a brief summary of your weight-of-evidence rationale.
The analysis showed that the year of the different national EQSs (e.g. older than the TGD) likely caused some variation. While other EU guidance and directives had been used frequently, the TGD had only been used for few of the selected substances. Furthermore, the protection endpoint and hence assessment factor used also contributed to the variation.
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