Hazardous Waste Classification: Review of Worst Case to Less Worst Case Metal Species With a Worked Example for a Contaminated Soil

Abstract

The classification of waste as either hazardous or non-hazardous, especially for mixtures such as contaminated soils, ashes, filter cakes and sludges, is not straight forward. In particular, as the laboratories can only measure total metal concentrations, both the European and the UK technical guidance state that if the classifier doesn’t know exactly which metal species is in their waste, then they should start from a worst case species and use lines of evidence to work towards a more reasonable (less hazardous) species. However, the guidance doesn’t define or list worst case nor less worst case species. While some authors have documented worst case species, this is only in relation to documenting the concentrations at which each hazard property is triggered for a given worst case species. This paper addresses this gap. It documents how to define both the worst case species and more importantly, lists less worst case species for 32 elements and 204 metal species; species based on those listed in the European legislation but also supplemented by species that haven’t (yet) been included in this legislation but are significant nevertheless. For each species, the paper tabulates the hazard property that triggers first, metal concentrations, conversion factors and other metadata, species by species, in descending order of hazard. Finally, to demonstrate how to use the data, either manually or by utilizing commercial software, the paper will give a worked example for a contaminated soil, showing how classifiers can use the list to help move from a worst case to a less worst case species.

Research to Industry and Industry to Research

“…Based on widespread analytical methods, the "indirect" approach is cheap and currently the most adopted. Notably, it is characterized by some challenges: the subjectivity of the "expert judgment," the impossibility of detecting all substances and elements that compose the waste material, and the so-called "worstcase" approach, which considers the waste constituents detected as in the most hazardous form (Bishop and Hennebert, 2021;Hennebert, 2019). These drawbacks have been limited by the development of non-targeted organic and mineral analyses, giving an analytical mass balance > 90% (Hennebert et al, 2013), and the speciation of socalled "worst-case with information" pre-calculated approaches (Hennebert, 2019).…”