Biobeschikbaarheid van essentiele metalen voor bodem-organismen: zinktitratie als middel ter bepaling van accumulatie en toxiciteit

Quality standards for heavy metals are based on the total amount of the metal present in the solid phase. In some cases risk limits are derived which are almost equal to the natural background concentration. Thereupon, it is insufficiently taken into account that some metals are essential for living organisms. These observations were ground for developing a conceptual framework for an improved risk assessment methodology that does take these aspects into account. As a first step towards implementation of the framework, toxicity tests were performed with natural substrates and biota that actually reside in these substrates. Thereupon, the bioavailability of the metals for the species tested is explicitly taken into account. It is concluded that integration of knowledge on soil chemistry (speciation and competition), the ecological characteristics of the test species, and the underlying mechanisms of toxicity do indeed enable future implementation of an improved methodology for risk assessment of heavy metals. It is shown that the dominant uptake routes for metals by specific classes of organisms as well as the presence of competing cations (especially H+) need to be specifically taken into account. The strategies employed by biota to detoxify accumulated metals could be used for developing improved risk assessment methodologies based upon internal metal levels as being the ultimate expression of bioavailability.