Schwermetalle in Klärschlamm und Müllkompost

Summary

Heavy metals in sewage sludge and garbage compost

Results of the 2nd interlaboratory comparison of concerted action COST 68^bis, working party 2

On the basis of the results of the 1st Interlaboratory Comparison (IC) of Working Party (WP) 2, presented already at the 1st European Symposium in Cadarache. the reasons are given why a 2nd IC had to be carried out.

Moreover, the experiences made under a similar programme of the Food and Agriculture Organisation (FAO) of the UN (European Research Network on Trace Elements) were used when preparing the 2nd IC, since some of the laboratories involved in COST 68 activities have been participants in the FAO programme.

This led to the conclusion that the analytical investigation of a “Test Solution” of pure metal salts had to be a necessary step of this IC. The test samples distributed by the Joint Research Centre Ispra consisted of a dried sewage sludge and a garbage compost sample in addition to the above-mentioned test solution. The latter had to be used for testing the accuracy of the methods, apparatus and laboratory standards of the participating laboratories. The participants were also supplied with operating procedures in respect of the pretreatment of samples and the methods of digestion that should, if possible, be used in addition to the preferred laboratory method.

These precautions turned out to be justified. It was seen from the results received from 38 laboratories in 9 countries that the instructions given had been essentially adhered to. However, there were some unexplained deviations from reference values for the test solution. Likewise, some of the results communicated did not admit of interpretation. At the session of WP 2 where the preliminary evaluation of the collaborative study was discussed, it was thus decided to circulate among the participants a questionnaire inquiring about details of the methodology used, in particular with regard to the method(s) of digestion. The answers are to provide more information on the techniques used and to permit a detailed interpretation of results. This will, in turn, enable an evaluation of the methods applied that goes beyond the scope of results generally obtained from collaborative studies. The experience gained in the present IC may be useful when having to make recommendations on the selection of suitable methods for the analysis of heavy metals in sludges and composts and thus contribute to the field of evaluation of the heavy metal contamination of such materials if used in agriculture.