Effects of sewage sludge amendment on the properties of two Brazilian oxisols and their humic acids.

The effect of sewage sludge (SS) amendment on the general properties of the top layers of a sandy and a clayey oxisols and on the nature of their humic acid (HA) fractions was evaluated by chemical and physico-chemical techniques. The amended soils, especially the sandy soil, benefited of SS amendment by increasing their pH to above neutrality and enhancing the contents of C, N, P, and Ca and cation exchange capacity. The SS-HA-like sample showed larger H and N contents and a greater aliphatic character and humification degree than the HAs isolated from non-amended soils. The composition and structure of amended soil HAs were affected by SS application as a function of soil type and layer. In particular, N-containing groups and aliphatic structures of SS-HA-like sample appears to be partially incorporated in the amended soil HAs, and these effects were more evident in the HAs from the sandy oxisol.

Influence of extractant on quality and trace elements content of peat humic acids.

Among several extractants used to isolate humic acids (HA) from terrestrial environments, sodium hydroxide (NaOH) and sodium pyrophosphate (Na(4)P(2)O(7)) are the most utilized. In order to evaluate the influence of these different extractant solutions on the HA quality and on their trace elements content, HA were isolated from five Sphagnum-peat samples using three different solutions: (a) 0.5M NaOH; (b) 0.1M Na(4)P(2)O(7); (c) 0.5M NaOH+0.1M Na(4)P(2)O(7). The obtained HA have been analyzed with respect to ash content, elemental composition, main atomic ratios and characterized by FT-IR and total luminescence (TL) spectroscopies. In addition, both raw peat and HA have been analyzed using X-ray fluorescence in order to determine the Br, Cu, Fe, Ni, Pb and Zn contents. Results showed that HA extracted with NaOH and NaOH+Na(4)P(2)O(7) are quite similar with respect to ash, elemental contents and spectroscopic characteristics, while Na(4)P(2)O(7) solution, which in general reduces the extraction yield, seems to affect the nature of HA, featuring a more complex and aromatic character. With respect to the contents in the corresponding raw peat samples, the HA fractions were richer in Br, Cu and Ni, regardless of the extractant used, and poorer in Fe, Pb and Zn. Further, Br, Cu, Ni and Zn were more concentrated in HA extracted with Na(4)P(2)O(7) than in those extracted with NaOH and NaOH+Na(4)P(2)O(7), probably because of the greater affinity of these elements for these more aromatic humic molecules.

Fluorescence analysis of humic and fulvic acids from two Brazilian oxisols as affected by biosolid amendment.

Conventional monodimensional fluorescence spectroscopy in the emission, excitation, and synchronous-scan modes and total luminescence spectroscopy have proven to be sensitive techniques for characterization and differentiation of humic acid (HA) and fulvic acid (FA) fractions isolated from an aerobically and anaerobically digested and limed biosolid, two layers of a sandy and a clayey Brazilian oxisol, and the corresponding biosolid-amended soils. The spectral patterns and the relative fluorescence intensities suggest greater molecular heterogeneity, less aromatic polycondensation, and less humification of biosolid HA and FA compared with soil HA and FA. However, the differences are smaller for the FA fractions than for the HA fractions. Fluorescence properties of soil HA and FA differ slightly as a function of soil type and soil layer. Biosolid application causes a shift to shorter wavelengths of the main fluorescence peaks and marked variation of the relative fluorescence intensities of HA and FA isolated from amended soils. These results suggest that molecular components of relatively small molecular size, with a low level of aromatic polycondensation, and low degree of humification present in biosolid HA and FA are partially and variously incorporated into amended soil HA and FA. In general, these modifications seem to be smaller in HA and FA from the clayey soil layers than in those from the sandy soil layers, possibly because of protective effects exerted by clay minerals of native soil HA and FA against disturbances caused by biosolid application.