Die Bodenkultur - Journal for Land Management, Food and Environment
M. H. GERZABEK, S. A. MOHAMAD, O. H. DANNEBERG and K. SCHAFFER:
Heavy metals in humic substances from a town refuse and a refuse-sewage sludge compost
The present paper deals with the extraction of humic substances and heavy metals from a town refuse compost and a refuse-sewage sludge compost. The chosen methods were extraction with a complexing ion exchange resin (Chelex 100) and with 0.1 molar Na4P207 and 0.1 molar EDTA (both adjusted to pH = 10.36). The most effective method was the extraction with EDTA, followed by Na-pyrophosphate. The EDTA extraction yielded between 9 and 61% of the total contents of the heavy metals. The ratio of the mean extraction yields was 1: 11: 17 for Chelex, Na-pyrophosphate and EDTA, respectively.
The second step was an exclusion chromatography of the Chelex- and EDTA extract (refuse-sewage sludge compost) on controlled pore glass. The salt volume of the column showed no detectable heavy metal concentrations. Thus the extracted heavy metals were entirely bound to high molecular weight organic compounds. The EDTA-extract expressed a heavy metal concentration maximum in the range of the fulvic acids whereas the Chelex extract showed high heavy metal concentrations preferably in the grey humic acid fractions.
Key words: compost, extraction, heavy metals, humic substances