Vurdering av biotilgjengelighetsmodeller som verktøy for karakterisering av resipienters sårbarhet for metallforurensing fra veg

Summary

Building, traffic and maintenance of road can lead to increased supply of metals to water bodies. The metals’ physico-chemical speciation and bioavilability toward aquatic organisms depend on water chemical variables such as pH, alkalinity, and the concentration of calcium and humic substances. The water framework directive’s environmental quality standards for annual mean concentration (AA-EQS) of lead and nickel therefore refers to the “bioavailable conentration”, and the same is likely for copper and zinc when new national EQS are set for river basin specific pollutants. This means that concentrations of dissolved metal higher than the EQS are permitted if e.g. pH, calcium and humic substances lower the bioavailability of the metals. This will have an appreciable effect on threshold values because of large regional differences in water chemistry. Several types of models have been developed in order to predict how water chemistry affects bioavailability. The purpose of the current work is to assess if simple tools can be useful for setting recipient specific threshold values for metals for building and operation of roads in Norway. It is, however, a challenge that up to 90 percent of Norwegian water bodies have pH or calcium concentrations below the validated range of the models. There are also indications that the models should not be used outside their validated ranges, especially without safety margins. There is a distinct need for tools that can be used to estimate bioavailable concentration in soft waters.