## 4 Discussion  
The classification of IBA as hazardous or non-hazardous according to hazard property HP14 ecotoxicity is still under debate because there are still no generally accepted methods for the assessment. Biotests with aquatic and terrestrial microorganisms are often suggested for ecotoxicity assessment [36]. Here, the exact chemical composition need not be known. Observed here is the effect of the aqueous leachate of the test material on the selected organisms. In the cited work, the leachate was prepared with an L/S of 10 L/kg and then diluted by factors of 2, 4, and 8. The leachate of a moderately aged IBA has a pH of 11 [21], and even with a dilution by a factor of 8, the resulting test solution has a pH higher than 8.5, which is, however, recognized as the maximum pH for biotests. At higher pH values, the test organisms already show effects due to the pH. The provided procedures for the application of biotests are not uniform in Europe. In Austria, the leachate is diluted by a factor of 1000 in compliance with the methods described in CLP [10], i.e., the final L/S is 10,000 L/kg or, finally, 100 mg IBA per L [37]. With this approach, IBA is, not surprisingly, usually classified as non-hazardous. There are approaches to elucidate the chemical composition of IBA by X-ray methods such as XAS, XRD, and XANES. The latter method even requires radiation from a synchrotron light source [38; 39; 40]. Although useful results are gained, the methods are not applicable for commercial analytical laboratories. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Cu** & **Zn** & **Cu\({}_{2}\)CO\({}_{3}\)(OH)\({}_{2}\)** & **ZnO** & **HP14 Sum** \\  & **(mg/kg)** & **(mg/kg)** & **(mg/kg)** & **(mg/kg)** & **(\%)** \\ \hline IBA1 & 430.82 & 1113.02 & 749.62 & 1380.14 & 13.8 \\ \hline IBA2 & 597.34 & 1132.59 & 1039.37 & 1404.41 & 24.4 \\ \hline IBA3 & 559.60 & 1231.01 & 973.71 & 1526.45 & 15.3 \\ \hline IBA4 & 746.52 & 886.56 & 1298.95 & 1099.33 & 24.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Extracted amounts of the elements Cu and Zn after selective extraction with maleic acid at pH 4 and conversion to the respective “worst-case” substances used for the calculation of the HP14 sum (calculation rule 2). This is different for the two methods applied in the present study. With the 4-step sequential extraction, the mobilization behavior of the relevant heavy metals can be examined. For the HP14 classification, even a one-step extraction (here, called selective extraction) might be sufficient. For IBA, only the elements Zn and Cu are of relevance because the solid content of all other heavy metals is below the cut-off value of 0.1% even when stochiometric factors are applied to convert them to chemical compounds. In this context, it is strange that for Pb the elemental concentration counts and no conversion is needed (\"Note 1\" in CLP, see above), although the toxicity coefficient T\({}_{\text{i}}\) of Pb (see Table 2) is as high as for Cu and higher as for Zn. Further, setting a cut-off value (here, 0.1%) leads to non-consideration of other heavy metals rather than Cu and Zn. However, a longer list of heavy metals is under consideration for landfilling or utilization of IBA [21]. In the series of experiments performed in the present study, the limit value for a classification as hazardous waste was exceeded for two samples due to Zn concentrations of around 2800 mg/kg extracted at pH 4. In both cases, the sum of all 4 fractions was then above 4000 mg/kg, which is above the medium value for Zn presented by [PERSON] et al. [16]. This could be the result of insufficient sample homogenization or the presence of small brass particles. In general, a sample size of 0.5 g for the described extractions is low in comparison to standardized leaching tests with L/S ratios of 2 or 10 L/kg. Here, the sample sizes are 500 or 100 g of waste material, respectively. Anyway, the results in the present study indicate that IBA is to be classified as non-hazardous waste.