Interactions of chlorine with tropical aquatic fulvic acids and formation of intermediates observed by fluorescence spectroscopy

The interactions of tropical aquatic fulvic acids (AFA) with chlorine and formation of trihalomethanes were characterized by fluorescence spectroscopy. The aquatic humic substances (AHS) were isolated from a dark-brown stream (located in a environmental protection area near Cubatão city in São Paulo State, Brazil) by means of the collector XAD 8 according the procedure recommended by the International Humic Substances Society. The photoluminescence measurements were made by using a Perkin Elmer spectrometer; AHS, aquatic humic acids (AHA) and AFA samples were assayed. The interactions of AFA and chlorine were characterized by using different reaction times (1, 24, 48, 72 and 168 h) and chlorine concentrations (2.5, 5.0, 10.0 and 20.0 mg L-1). The relative fluorescence intensity for AFA was significantly decreased with the increasing of chlorine concentration and reaction time. The reduction of fluorescence intensity in the region of longer wavelength was interpreted as an indicative of interaction between condensed aromatic groups of AFA and chlorine

Soil organic matter in podzol horizons of the Amazon region: Humification, recalcitrance, and dating

International audienceCharacteristics of soil organic matter (SOM) are important, especially in the Amazon region, which represents one of the world's most relevant carbon reservoirs. In this work, the concentrations of carbon and differences in its composition (humification indexes) were evaluated and compared for several horizons (0 to 390 cm) of three typical Amazonian podzol profiles. Fluorescence spectroscopy was used to investigate the humic acid (HA) fractions of SOM isolated from the different samples. Simple and labile carbon structures appeared to be accumulated in surface horizons, while more complex humified compounds were leached and accumulated in intermediate and deeper Bh horizons. The results suggested that the humic acids originated from lignin and its derivatives, and that lignin could accumulate in some Bh horizons. The HA present in deeper Bh horizons appeared to originate from different formation pathways, since these horizons showed different compositions. There were significant compositional changes of HA with depth, with four types of organic matter: recalcitrant, humified, and old dating; labile and young dating; humified and young dating; and little humified and old dating. Therefore, the humification process had no direct relation with the age of the organic matter in the Amazonian podzols

Hidrofobicidade em Neossolo litólico sob plantação de Pinus taeda

The understanding of soil carbon stabilization processes can be very useful in the development of mitigation techniques for CO2 emissions and global warming. The greater the hydrophobicity of soil organic matter the more stabilized soil organic carbon. Therefore,  hydrophobicity can be a sensitive index to characterizethe ‘quality’ of soil organic matter. In this context, the present work aimed to characterize the chemical  structures of humic acids collected at three different depths in a hydrophobic Entisol (Neossolo) under  loblolly plantation. The results of spectroscopic and chemical analyses (UV-Vis, fluorescence, EPR and X-ray diffractometry) indicated that, as soil depth increased, so did the content of conjugated organic structures, aromatic groups, and free organic radicals, leading to higher humification indices. Aliphatic groups in these fractions were more concentrated in the surface layer than in deeper ones, which can be explained by the constant input of litter. The greater hydrophobicity of the surface soil sample was due to these non-humic components of the organic matter, as suberin and cutin.doi: 10.4336/2010.pfb.30.62.93Compreender os processos de estabilização do carbono no solo pode ser muito útil no desenvolvimento de técnicas de mitigação das  emissões de CO2 e do aquecimento global. Quanto maior a hidrofobicidade da matéria orgânica do solo, mais estabilizado é o carbono do solo. Portanto, a  hidrofobicidade pode ser usada como indicador para  caracterizar a qualidade da matéria orgânica do solo. O presente trabalho caracterizou as estruturas  químicas de ácidos húmicos extraídos de solos  coletados a três profundidades de um Neossolo sob plantação de Pinus taeda. Os resultados das análises  espectroscópicas e químicas (ultra-violeta,  fluorescência, ressonância paramagnética eletrônica e difração de raio-X) indicaram que a ocorrência de  estruturas conjugadas, grupos aromáticos e radicais orgânicos livres e, portanto, maiores índices de  humificação, aumentaram com a profundidade do  solo. Grupos alifáticos na fração húmica estavam  mais concentrados nas camadas superficiais, o que pode ser explicado pelo constante aporte de liteira na superfície. Testes da repelência à água apontarammaior hidrofobicidade na superfície do solo, provavelmente devido a componentes não húmicos da matéria orgânica, tais como suberina e cutina. doi: 10.4336/2010.pfb.30.62.9