Changes in optical properties caused by UV-irradiation of aquatic humic substances from the amazon river basin: seasonal variability evaluation

Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by 13C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence, and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching up to 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO2, CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.     

Long-term lime and phosphogypsum broadcast affects phosphorus cycling in a tropical Oxisol cultivated with soybean under no-till

Nutrient Cycling in Agroecosystems - Broadcast application of lime or phosphogypsum to suppress aluminum (Al) in soils can influence chemistry and fate of phosphorus (P) in natural environments....     

用合成腐植酸模型研究腐植酸中铜(Ⅱ)的吸附行为

在碱性条件下,以对苯醌、对苯二酚和4-氨基苯甲酸3种物质为前体,通过氧化聚合反应可以得到类似腐植酸性质的聚合物。用天然及合成腐植酸样品研究腐植酸对Cu2+的吸附作用。通过Langmuir和Freundlich等温吸附方程式来建立数学模型,进而计算出最大吸附强度K′(Langmuir)、最大吸附容量b(Langmuir)和吸附剂最大吸附容量m(Freundlich)。基于溶解度的研究,我们选择在pH3下进行吸附试验研究。在Langmuir吸附等温式中,RL(平衡参数)表示Cu2+的吸收情况。试验表明,在适当范围内,Cu2+呈现出良好的吸附效果。     

Identification of irradiation treatment in black pepper by electron paramagnetic resonance

Electron paramagnetic resonance spectroscopy was applied to study free radicals in black pepper, and to evaluate the potential of these radicals in identifying radiation treatment. A doublet signal was detected at g = 2.0042 and a = 1.83 mT, produced exclusively by radiolysis. This signal is as stable as that of irradiated cellulose, and can be used to identify recent radiation treatment. A line produced both by radiolysis and thermolysis was observed, and its behaviour with thermal treatments suggests that it cannot be used as an irradiation indicator for doses up to 30 kGy, contradicting a model proposed in the literature.     

Hydrophobic interactions between spin-label 5-SASL and humic acid as revealed by ESR spectroscopy

The spin-label probe 5-SASL (stearic acid spin-label with nitroxide free radical in position 5 of hydrocarbon chain), detectable by electron spin resonance (ESR), was tested to evaluate pH and reaction time dependencies of hydrophobic interactions with humic acid (HA). Strong changes were observed in 5-SASL ESR spectra in the presence of HA suspensions below pH 5, with disappearance of the three isotropic narrow hyperfine lines of the nitroxide group (typical of free spin-label) and formation of "immobilized" 5-SASL spectra. These changes were interpreted as due to 5-SASL bonding with hydrophobic groups of HA, by van der Waals forces and/or hydrogen bonds, in very hydrophobic sites (probably water-protected) existent in HA below pH 5. However, such sites are absent above pH 5, as demonstrated by a specific experiment to check 5-SASL spectra reversibility. On the other hand, the HA suspension was more efficient in dissolving 5-SASL than water above pH 5. This fact also suggests the existence of "surface" hydrophobic sites, where the spin-label binds to HA while maintaining the nitroxide group in contact with water, as evidenced by the typical free spin-label spectrum and hyperfine interaction splitting (a0 = 1.574 mT). Also experiments checking 5-SASL reversibility bonding with HA were consistent with the supramolecular association model to HA.     

Oxidative decomposition of atrazine by a Fenton-like reaction in a H2O2/ferrihydrite system

The oxidation of atrazine (ATZ) was studied in the presence of hydrogen peroxide (H(2)O(2)) and ferrihydrite at different concentrations and pHs. The rate of ATZ oxidation increased with H(2)O(2) concentration and is independent of pH ranging from 4 to 8. However, at pH 3 an increase of ten times in the rate of ATZ oxidation was observed due to the mineral dissolution. The decomposition rate of H(2)O(2) was three times higher at pH 8 than 3 and increased with increase of both H(2)O(2) and ferrihydrite concentrations. The results indicate that ferrihydrite controls oxidation of ATZ by H(2)O(2) in two different ways: (i) mineral dissolution at low pH allowing the Fenton reaction to proceed in solution and (ii) surface-mediated decomposition of H(2)O(2) producing non-reactive oxygen species in particular at higher pH. Three degradation products (desethylatrazine, desisopropylatrazine, and 2-hydroxyatrazine) were identified and corroborate with a Fenton reaction taking place in solution.