Huidige mogelijkheden en inzichten voor implementatie van metaalbiobeschikbaarheid in de risicobeoordeling van landbodems

Metals are naturally occurring compounds and some of them are essential for survival of organisms. These aspects are directly related to the effects of metals in ecosystems, and should explicitly be taken into account in risk assessment procedures for metals that usually operate through total concentrations. Thereupon, the aspect of bioavailability has insufficiently been taken into account in current methodologies for risk assessment. Recently, the insight has increased in the chemical and biological processes that jointly deter-mine the availability of metals for the biota that comprise the eco-systems. In this report a review is given of the current scientific possibilities for taking differences in bioavailability of heavy metals into account in future risk assessment and standard setting. It is concluded that there are indeed such possibilities. Currently, however, lack of suited data and insights hinder the development of a modified system for risk assessment and standard setting that is 'better' capable of predicting actual effects in soil ecosystems than current methodologies. A general concept is being presented that might serve as a basis for the modified system. Within the concept it is assumed that adverse effects will occur only when a species-, soil- and metal-specific critical value is exceeded. A new system of risk assessment could be based upon two sets of toxicity data: one data-set for species that are exposed via the pore water, and one set for species for which uptake via the solid phase is the dominant uptake route. Nevertheless, both risk assessment and standard setting could in the new system still primarily be based upon total metal concentrations in the soil solid phase. At present, there appear to be insufficient data and well-defined conceptual frameworks to allow for implementation of a modified system. In the report a prioritization of additional research needs is therefore included.