No abstract

Mass spectra (MS) in positive and negative ionization mode of different humic substances (HS) and dissolved organic matter (DOM) were measured using electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) as transfer ionization techniques. With APCI the average molecular masses were reduced by a factor of 4 to 6 compared to the softer electrospray ionization. This might be the result of breaking charge-transfer bonds, hydrogen bonds or weak covalent bonds between DOM molecules. The calculated average molar masses of HS were in a range as reported by other authors. For bound anilazine residues ESI and APCI were used combined with selective reaction monitoring (SRM), a MS/MS technique for the quantification of specific molecules in a complex mixture. Applying APCI we found a high release of the main anilazine metabolite dihydroxyanilazine. These amounts were similar to those obtained by silylation, a technique reported to release sequestered pesticides. Furthermore, the release corresponding to molecular weight of bound residues was analyzed. Anilazine is bound to all molecular weight fractions as was revealed by size exclusion chromatography (SEC) with radioactivity and APCI−SRM detection. In addition, we tested the matrix effects of different HS with APCI revealing a deviation of the correlation of measured MS signal intensity in function of ingredient concentration that depended on the type and concentration of HS.

The stability of soil bound metabolites of 2,4,6-trinitrotoluene (TNT) was investigated. Highly TNT-contaminated soil from a former production site was spiked with [ring-UL-14C]TNT. An anaerobic short-term treatment (8 days) was carried out and compared with a previously described long-term anaerobic (51 day) treatment. In the short-term experiment the anaerobic treatment was stopped to examine the early-stage effects of the reduction process on the stability of TNT derivatives in soil at the time of the maximum accumulation of aminodinitrotoluenes, whereas the long-term anaerobic treatment was continued until the formation of triaminotoluene. In contrast to the soil from long-term anaerobic treatment, no significant reduction of aminodinitrotoluenes to diaminonitrotoluenes was observed after short-term anaerobic treatment, and the binding of reduced metabolites to the soil was incomplete. In both experiments the anaerobic phase was followed by an aerobic treatment. After the short-term anaerobic/aerobic treatment only 40% of the initial radioactivity was bound to the soil compared to 98% after the extended anaerobic incubation. A significant amount of this bound radioactivity could be released into organic solvents by silylation. The silylation extracts were analyzed by thin-layer chromatography and radiocounting. The released radioactivity from silylation after the long-term treatment was attributed to polar compounds cross-linked with humic material. For the silylated extracts after short-term anaerobic treatment conditions, a significant amount of released radioactivity (28%) found in fractions was attributed to TNT and aminodinitrotoluenes. This study indicates that with a shorter duration of the anaerobic phase in the overall treatment, physically entrapped (sequestered) metabolites remain in the soil. To eliminate physical entrapment, TNT derivatives should be completely reduced by a sufficiently extended anaerobic treatment.