19 Mar 2015

Assessing the bioavailability of metals in freshwater

DHI recently completed a study to determine whether two tools used to assess the bioavailability of metals in freshwater could be applied for conditions in Denmark.

Bioavailability indicates the fraction of the dissolved concentration of a substance that is freely available for uptake in aquatic organisms. Factors that affect the uptake of metals include pH, hardness of the water, and the presence of organic material. 

Revised European Union environmental quality standards (EQS) for nickel and lead must be implemented in Danish legislation by September 2015. These EQS are important to both manufacturing companies discharging wastewater and local authorities granting the discharge permissions.

The revised EQS include the need to account for bioavailability in the regulation of metals in freshwaters, which is a relatively novel regulatory approach. It is also a considerable change from the existing ways of working with risk assessment of metals.

The Danish Nature Agency initiated a study to determine if available tools for assessing the bioavailability of metals in freshwater – Bio-Met and M-BAT – are valid and relevant under the geochemical conditions in Denmark. On behalf of the Danish Nature Agency, we used these two tools to assess the bioavailability of copper, nickel and zinc in freshwater in Denmark.

We found that both Bio-Met and M-BAT gave valid results for conditions in Denmark. We also determined that physico-chemical characteristics – pH, calcium concentration, and dissolved organic material – significantly influence the bioavailability of these metals. This consequently affects compliance with the environmental requirements. More information about the study can be found here.