Ageing of dissolved halogenated humic substances and the microbiological influence on this process

The distribution of halogens in various fractions of humic substances (HS), separated by their molecular weight, was found to be different for the dif ferent halogens. This was demonstrated for chlorine, bromine, and iodine in sewage and brown water samples by applying inductively coupled plasma mass spectrometry coupled with size-exclusion chromatography. Quantification of the different fractions of iodinated humic substances was obtained by quad rupole mass spectrometry in connection with the isotope dilution technique using an I-129-enriched splice solution. Quantitative analysis was not poss ible for the corresponding chlorine and bromine species because of spectrom etric interferences in the quadrupole instrument. The ageing of HS/halogen species was followed with respect to possible transformations of these spec ies in a ground and sewage water sample up to eight weeks. Even if a distin ct structural variation of the humic substance was observed with time by me asuring the UV absorption, chlorine remained in the same molecular weight f raction and only a small change was found for the HS/bromine species after eight weeks. In contrast to these findings a substantial transformation of HS/iodine compounds took place, which demonstrated that the transfer probab ility of halogens from one to another HS fraction is increased with decreas ing strength of the halogen bond to carbon. By comparing the results of an original sewage water sample with a filtered one and with another one which was enriched by microorganisms cultivated from the same original sample, a strong microbiological influence on the transformation of HS/iodine specie s was found. A quantitative balance of the corresponding HS/iodine fraction s was calculated for an ageing period of right weeks showing that iodine wa s preferably transferred to newly formed UV active HS substances of high mo lecular weight. In total, no iodine was released from the humic substances.