Investigations on the binding mechanism of the herbicide XXXX to dissolved organic matter in leachates of compost.

@entity14458 @entity13304 @entity3209
@entity3209 -labelled @entity14458 was composted together with biowaste on a pilot (m3) scale. The herbicide was quickly bound to the compost matrix. By aqueous extraction of 29 and 200 days old compost (equivalent to thermophilic and mesophilic phase of composting) only 4.2% and 3.1% respectively of the radioactivity in the compost samples could be extracted with water. Analysis of the extracts using high-performance size exclusion chromatography (HPSEC) revealed that the dissolved organic matter ( @entity13304 ) had molecular weights ranging between 2 and 28 kDa. The amount of @entity13304 -associated radioactivity increased from 53% (day 29) to 65% (day 200) of total extractable radioactivity. The type of binding of the @entity3209 -labelled residues and the @entity13304 was elucidated by silylation of humic matter and subsequent HPSEC. The data demonstrated that besides polar metabolites also intact @entity14458 was bound to the @entity13304 . A distinct shift from rather weak interactions to strong covalent linkages of @entity14458 and its metabolites with increasing age of the compost was observed. The results showed that only low amounts of free @entity14458 and its degradates can be extracted with water. We concluded that the shift towards stable covalent linkages is equivalent to a detoxification of the contaminant in aged compost. Consequently, the use of the analysed compost in its mature stage should not pose an environmental risk to the groundwater or the subsoil.
