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This report describes the results of a research programme on the application of the so-called TRIAD approach for site specific ecological risk assessment of soil pollution. The method means to optimise the estimation of actual ecological effects in a specific area or ecosystem, by gathering multiple evidence along various ways. The TRIAD includes three pillars consisting of chemical, toxicological and ecological measurements. Each pillar of the TRIAD can be extended over three tiers, representing low, middle and high levels of sophistication in research methods. In the second phase of the field research, three locations were investigated with emphasis on the selection of a local reference site and ecological measurements. The chemical, toxicological and ecological measurements were integrated into an effect estimation per TRIAD-unit and one overall assessment. Effects were scaled from 0 to 1 and divided into 3 colour-categories to obtain a better overview. Although most bioassays and ecological indicators were able to characterise the samples, they showed much lower effects than predicted from the measured concentrations of pollutants. The (chemical) Toxic Pressure method, based on Species Sensitivity Distributions, seems to give an overestimation of ecological effects. It is also less discriminating in situations of multiple substance pollution exceeding Serious Risk Levels.

The TRIAD approach was tested for its applicability in assessing actual ecological risks on five sites around the zinc factory near the city of Budel, in The Netherlands. The TRIAD method offers the possibility of a tiered approach to actual risks for the local ecosystem. Risk assessment is derived on the basis of three elements, i.e. chemistry, toxicology and ecology. It is meant as an improvement for the present remediation urgency systematics. Three of the five sites were contaminated with zinc and cadmium at different levels, that did not exceed the Dutch 'intervention values'. Besides total soil contents, mobile soil metal fractions and pore-water concentrations were measured during the chemical assessment. Several variants of the toxic pressure calculations were compared. In the toxicological assessment several bioassays were performed, which showed different sensitivities to heavy metals and influence of soil-pH and nutrients. There are still very few tests that can be used for acid sandy field soil. Many soil biological analyses (microbial and soil fauna groups) and a vegetation inventory were used for the ecological assessment. In this field study they showed a larger deviation from the reference site than the chemical and toxicological indicators. From the overall TRIAD assessment it can be concluded, among others, that selection of a non-contaminated reference site is both crucial as well as difficult. Polluted sites generally differ in more aspects from a local reference site than just in the concentration of contaminants. Although the TRIAD approach is relatively time consuming, uniformity and the scientific basis of the actual ecological assessment have improved considerably. Therefore the TRIAD approach is recommended for the future as a standard tool to assess actual ecological risks of contaminated soil.