The water-soluble fraction can be quantified with standard leaching procedures, e.g., at liquid to solid ratios (L/S) of 2 or 10 L/kg. Both sulfates of Zn and Cu belong to this group. In a recent publication, it was shown that for the above-mentioned metals the leached amount is well below the cut-off value of 1000 mg/kg even when the stochiometric factors are applied [21]. Substance group 3 includes potential H410 substances. These are carbonates, hydroxides, and oxides of the listed elements, and are soluble in weak organic acids such as acetic acid. The \"worst-case\" substances in group 3, i.e., those compounds with the highest stochiometric factors, are CuCO\({}_{3}\times\)Cu(OH)\({}_{2}\) (factor 1.74) and ZnO (factor 1.24). ZnCO\({}_{3}\) would have a higher stochiometric factor (1.92) but is classified as H411 only. Substances with strong chemical bonding, such as silicates or sulfides, are only soluble in strong acids (e.g., aqua regia) and have no hazard statement code for ecotoxicity. Sequential extractions are a viable method for distributing elements into different substance groups, as outlined above. They were initially developed to investigate the chemical composition of soil and sediments [22]. The procedure was harmonized for the determination of extractable trace metals in sediments by the Community Bureau of Reference (BCR) [23], but is often modified. [PERSON] and [PERSON] [24] proposed a 7-step extraction procedure starting with water extraction and no pH adjustment. A comprehensive review on sequential extraction was presented by [PERSON] et al. [25]. Although the individual steps can vary, the common approach is using increasingly stronger leaching liquids within the sequence. Usually 4 fractions (F) are generated and analyzed: F1 bound to carbonates (weak acidic conditions), F2 bound to Fe- and Mn-oxides (reducing conditions), F3 bound to organic matter (oxidizing conditions), and F4, the residual fraction, only soluble in strong acids. Investigations on sequential extraction of IBA have already been conducted [24; 26; 27]. From the sequential extraction results, [PERSON] and [PERSON] [27] determined a risk assessment code and an individual contamination factor. [PERSON] et al. [28] used their results from sequential extraction with MSW IBA and sewage sludge incineration (SSI) fly ash to calculate the synthesis toxicity index (STI) [29; 30]. The STI allows evaluation of the potential toxicity of heavy metals in ashes. It was shown that vitrification of the ashes lowered the STI by several orders of magnitude. In the present study, four different bottom ashes from municipal solid waste incineration (MSWI) plants in Germany (IBA1-4), a fly ash from MSWI (waste code 19 01 13\") without flue gas cleaning products (FA), an SSI ash (SSA), and crushed sand (CS) from construction waste (waste code 17 01 07) were examined by a four-step sequential extraction procedure. The STI was calculated for all seven materials. For the four IBA samples, an assessment according to the hazard property HP14 (ecotoxicity) was carried out with a one-step extraction with an organic acid (maleic acid) at a pH of 4. This method could be an alternative to biotests in the classification of incineration bottom, according to the hazard property HP14.