Deriving a bioavailability-based zinc environmental quality standard for France.

National Environmental Quality Standards (EQS) for zinc used for the assessment of ecological status in freshwaters have been shown to vary by over two orders of magnitude across 25 European countries. Such variability is unlikely to reflect consistent ecological protection or environmental relevance. Recent European technical guidance on EQS derivation gives an opportunity to derive protective metrics for zinc that are relevant to national water chemistry conditions. To derive a zinc EQS relevant to national water chemistry conditions and account for bioavailability, the new technical guidance requires high-quality spatial and temporal monitoring data. These data must be of water samples with concurrent measures of pH, dissolved organic carbon (DOC) and calcium, the parameters that most influence zinc bioavailability in freshwaters. A national bioavailability-based zinc EQS for France has been derived from Biotic Ligand Model calculations undertaken for freshwaters samples from 4645 sites (22,000 samples with concurrent measures of pH, DOC, calcium) in 96 regions. An EQS of 11.3 μg Zn L-1 was derived based on sensitive waters from the Bretagne region typically of circumneutral pH and relatively low DOC and low dissolved calcium. The least sensitive waters to zinc exposures in France are found in the Hauts-De-France, higher pH values than those in Bretagne, similar dissolved organic carbon and higher dissolved calcium. An indicative assessment of compliance showed that across France, 2% of the sites would exceed this bioavailability-based EQS.