November 8, 2012 by Graham Merrington


bio-met.net is a website developed to guide those interested in using bioavailability-based approaches for assessing the risk of metals in the freshwater aquatic environment, particularly within the EU Water Framework Directive. bio-met.net is intended as a “one-stop shop” of information, software and guidance. The bio-met site is currently focussed on copper, nickel and zinc, but may be extended in the future to include other metals.

In response to EU discussions on the role of bioavailability during EQS derivation and compliance assessment for metals under the Water Framework Directive the UBA commissioned a study on the feasibility of the application of the bio-met bioavailability tool to German freshwaters. The study was undertaken by the Fraunhofer Institute and identified that for some types of waters, especially those of pH greater than 8 and with calcium concentrations less than 5 mg/L, the applicability ranges of the Biotic Ligand Models (BLMs) that underpin the bio-met tool limited their potential for regulatory use in Germany. The applicability ranges of the individual BLMs represent the extremes of water chemistry at which the chronic ecotoxicity tests used to confirm biological responses predicted by the models were undertaken. They are usually constrained by the physiology of the species routinely used for ecotoxicity assessment in laboratories and do not mean that BLMs cannot predict toxicity outside these ranges, just that the predictions are more uncertain.

In light of these concerns EU-wide freshwater data was assessed to ascertain the BLM applicability ranges that would be required to cover the majority of all EU waters. Based on this assessment, increasing the current pH boundary to from 8.0 to 8.5 and reducing the calcium boundary from 5 to 3 mg/L would achieve the 5th to 95thpercentile range of EU waters.

These ranges will be extended through a programme of ecotoxicity testing, which will be used to modify the BLMs and subsequently the bio-met.net tool. The new ranges will be available early in 2013 and will be:

MetalpHCa (mg/L)DOC (mg/L)
Zn6-8.53-160*30
Ni6.5-8.72-88*30
Cu6-8.53.1-16030

* These upper limits reflect only where the “protective” effect of Ca ceases irrespective of higher Ca concentrations. Above these values the EQS will still be protective of aquatic life.