Environmental Applications

Environmental samples studied by pyrolytic techniques encompass soil, water, and air. Although primarily studied for their possible role in soil fertility and stability, as discussed in the previous section, it is now recognised that humic substances play an important role in environmental problems because of their capacity for binding large amounts of organic and inorganic substances such as pesticide residues and heavy metals, which constitute potential environmental threats (ref. 189). A Curie-point Py-MS study of the organic fraction of river sludge samples from the Rhine delta, containing relatively high heavy metal concentrations, was recently reported by Van de Meent et al. (ref. 190). Although heavy metals appear to be effectively trapped by the strong chelating action of fulvic acids and other organic fractions, drastic changes in sediment pH or other physicochemical parameters might possibly lead to a sudden release of these metals into the environment. As a consequence, further studies of the organic structure and chelating properties of soil humic compounds in marine and terrestrial environments are strongly indicated.

An artificial "soil" unusually rich in organic compounds, but probably influenced by the same microflora as active in natural soils, is sewage sludge. Figure 46 shows spectra of aerobic and anaerobic sewage sludge. The pattern of the aerobically degraded sludge shows dominant protein patterns presumably derived from the bacterial cell mass composing most of the organic material. Other noteworthy features are the large nitric oxide peak at m/z 30, derived from pyrolytic degradation of nitrates, and the series of phenolic peaks in the higher mass range, typical of lignin thus showing the unusual resistance of this plant polymer against microbial degradation. As shown by De Leeuw (ref. 191), the lignin contribution in sewage sludge is mainly derived from toilet paper. The anaerobic (fermented) sludge spectrum is dominated by series of polysaccharide peaks, either signifying a basic difference in the composition of anaerobic microorganisms or showing the presence of incompletely degraded

Figure 46. Pyrolysis mass spectra of sludge samples from an aerobic (Pasveer ditch) and an anaerobic (fermentative) sewage treatment plant. The arrows in the upper spectrum point to a typical lignin series at m/z 124, 138, 150 and 164. The arrows in the lower spectrum reveal an ion series (m/z 109, 125, 137 and 151) characteristic of N-acetylamino sugars. For further biochemical interpretation, see text. Conditions: samples 20 ug; Tc 610°C; Egl 15 eV.

Figure 46. Pyrolysis mass spectra of sludge samples from an aerobic (Pasveer ditch) and an anaerobic (fermentative) sewage treatment plant. The arrows in the upper spectrum point to a typical lignin series at m/z 124, 138, 150 and 164. The arrows in the lower spectrum reveal an ion series (m/z 109, 125, 137 and 151) characteristic of N-acetylamino sugars. For further biochemical interpretation, see text. Conditions: samples 20 ug; Tc 610°C; Egl 15 eV.

carbohydrate input materials. The anaerobic nature of the sludge is demonstrated well by the strong NH3 peak at m/z 17 and the HgS and S2 peaks at m/z 34 and 64, respectively. A remarkable feature is the presence of Sg+' and Sg+" ions at m/z 160 and 192, respectively. Separate experiments showed these signals to be derived from electron impact ionization of Sg, formed by direct evaporation of elemental sulphur, present in the sample. The molecular ion peak (at m/z 256) is outside the mass range of this spectrum. At the higher end of the mass scale a typical N-acetylamino sugar series is found (at m/z 109, 125, 137, 151), possibly derived from the muramic acid moieties of bacterial cell walls. The ability of Py-MS techniques to characterise sludges is potentially valuable in the process control of slude treatment procedures as well as in judging the suitability of sewage and other sludges for recycling as cattle food, soil fertilizer or building material.

The possibility of characterising water samples by Py-MS is illustrated in Figure 47, showing spectra obtained from single drops of water taken from the inlet and outlet systems of anaerobic and aerobic sewage treatment plants. The lower mass range of the spectra shows the obvious decrease in organic signals after treatment in both cases. However, whereas the aerobically treated water is extremely rich in

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