Horizontal Standardization and Harmonization of Leaching Test Methods for Waste, Secondary Raw Materials, Construction Materials and (contaminated) Soil

In recent years, a lot of work has been carried out in evaluating environmental impact from a wide variety of materials in a wide range of different applications. The continously recurring inability to compare results between different jurisdictions and between disciplines can be resolved by focusing on a limited number of key test methods. This does require the recognition that many existing tests can be placed in perspective to a limited number of characterization leaching tests, and thus choices have to be made based on the relevance of the various test for specific purposes. The leaching behaviour of specific constituents is not dictated as much by material-specific factors, but is rather a function of key controlling factors common to many materials. The key factors controlling leachability in all matrices are pH, organic matter content and DOC, redox and salt load. Similarities in leaching behaviour between widely different types of materials need to be exploited further. Development of a European database/expert system in support of EU regulations would be very beneficial for regulators and users. A framework approach, suitable for the different fields of interest, is illustrated by example comparisons in which aspects are adressed such as characterization versus compliance testing, similarities in behaviour, scenarios for impact assessment, relationships between laboratory and field data. INTRODUCTION In recent years a lot of work has been carried out in evaluating environmental impact from a wide variety of materials in a wide range of different applications (WASCON, 1997, 2001). A continously recurring problem in such activities is the inability to compare results between different jurisdictions and between disciplines (Van der Sloot et al, 1997). Misconceptions between fields are generally discussed at the level of test use and test development, whereas it should be placed at the level of judgement of impact. The leaching behaviour of specific constituents is not dictated as much by material-specific factors, but is rather a function of key controlling factors common to many materials. For instance, Cu leaching is very strongly dominated by interaction with particulate and dissolved organic matter (DOC) in many matrices (van Zomeren et al, 2003; van der Sloot, 2002). The key factors will thus be pH, organic matter content and DOC rather than the fact one is dealing with different materials in different application scenarios. Due to the strongly vertically organized nature of standardization bodies the process of horizontal standardization is not facilitated. Below aspects of test comparison, constituent behaviour, common controlling factors, release mechanisms, modeling aspects and impact scenarios are discussed. COMPARISON OF DIFFERENT TEST METHODS Worldwide many leaching tests are used (Compendium, 1990). Many of those largely address the same aspects of leaching under slightly different conditions. Others are very different in the concept behind the method, such as the seqential chemical extraction procedure. Based on a comparison of methods and test data the pH dependence test has been identified as a method that allows mutual comparison of several different test methods (van der Sloot et al, 1997). This aspect of the method is illustrated in figure 1 and figure 2 for a random selection of elements from a heavily contaminated harbour sediment and from a heavily contaminated sewage sludge amended soil (CSO2). The agreement between the different tests – CaCl2 extraction, EN 12457, NaNO3 extraction, acetic acid extraction and sequential chemical extraction carried out on the same materials is highly encouraging. An indication of the repeatability of the method can be obtained from the duplicate test data. Obviously, the EDTA extraction does not fit the pH dependent leaching pattern as EDTA complexation is almost independent of pH. In fact, very similar results to EDTA extraction can be obtained at low pH, so if the aim is to assess an availability level, just extraction at low pH would likely suffice. The latter option is even better as EDTA is not equally effective for all constituents of interest and an extraction at low pH is more effective for a wide range of elements. The results from the sequential chemical extraction are calculated as a cumulative leached quantity at the pH corresponding to the subsequent more aggressive extraction step. Particularly, in the case of the sediment, where the pH dependence test was carried out over the full pH range covered by all other test methods the agreement is very good. For comparison purposes the total composition is included as a horizontal dashed line. The element specific leaching curve obtained with the pH dependence test can thus be seen as a material characteristic. This applies to metals, oxyanions, major and minor elements and DOC. Here only a limited number of parameters are shown, but the same observation extends a wide range of other constituents (ECN, 2003). In figure 2 pH ranges related to specific questions and data use are given in the pH curve reflecting Pb and Cr leaching from heavily sewage sludge amended soil. Obviously, the relevant pH range for a given application may be limited. However, for characterisation purposes the full pH range from at least 4 to 12 is important as the different potential uses of the information can cover this full pH range. In addition, for geochemical modelling purposes the full pH range is also very relevant. The sensitivity to pH change is obtained from the acid neutralization capacity (ANC). This parameter can be used to assess for a given situation what pH change can be expected from a certain stress, or what acid or base input would cause a shift into a more critical pH domain. The pH dependence leaching tests is recommended as basis of reference for all extended material evaluation and test methods. Figure 1. Heavily contaminated river sediment (Van der Sloot, 2002, SMT4-CT96-2066, 2003). Comparison of different leaching tests procedures: pH dependence test, EN 12457-2, CaCl2 extraction, and sequential chemical extraction. For comparison the total composition is included as a horizontal dashed line. 0.1 1 10 10