. A class of organic molecules extracted from atmospheric aerosol particles and isolated from fog and cloud water has been termed HUmic-LIke Substances (HULIS) due to a certain resemblance to terrestrial and aquatic humic and fulvic acids. In light of the interest that this class of atmospheric compounds currently attracts, we comprehensively review HULIS properties, as well as laboratory and field investigations concerning their formation and characterization in atmospheric samples. While sharing some important features such as polyacidic nature, accumulating evidence suggests that atmospheric HULIS differ substantially from terrestrial and aquatic humic substances. Major differences between HULIS and humic substances, including smaller average molecular weight, lower aromatic moiety content, greater surface activity, better droplet activation ability, as well as others, are highlighted. Several alternatives are proposed that may explain such differences: (1) the possibility that mono- and di-carboxylic acids and mineral acids abundant in the atmosphere prevent the formation of large humic "supramolecular associations"; (2) that large humic macromolecules are destroyed in the atmosphere by UV radiation, O3, and OH- radicals; (3) that "HULIS" actually consists of a complex, unresolved mixture of relatively small molecules rather than macromolecular entities; and (4) that HULIS formed via abiotic and short-lived oxidative reaction pathways differ substantially from humic substances formed over long time periods via biologically-mediated reactions. It should also be recalled that the vast majority of studies of HULIS relate to the water soluble fraction, which would include only the fulvic acid fraction of humic substances, and exclude the humic acid (base-soluble) and humin (insoluble) fractions of humic substances. A significant effort towards adopting standard extraction and characterization methods is required to develop a better and meaningful comparison between different HULIS samples.

/pdf/atmospheric-hulis-how-humic-like-are-they-a-comprehensive-4eo3w54c0b.pdf

Atmospheric HULIS: How humic-like are they? A comprehensive and critical review

Residues of pharmaceutical antibiotics are found in the environment, whose fate and effects are governed by sorption. Thus, the extent and mechanisms of the soil sorption of p-aminobenzoic acid and five sulfonamide antibiotics (sulfanilamide, sulfadimidine, sulfadiazine, sulfadimethoxine, and sulfapyridine) were investigated using topsoils of fertilized and unfertilized Chernozem and their organic-mineral particle-size fractions. Freundlich adsorption coefficients (K(f)) ranged from 0.5 to 6.5. Adsorption increased with aromaticity and electronegativity of functional groups attached to the sulfonyl-phenylamine core. Adsorption to soil and particle-size fractions increased in the sequence: coarse silt < whole soil < medium silt < sand < clay < fine silt and was influenced by pH. Sorption nonlinearity (1/n </= 0.76) indicated specific interactions with functional groups of soil organic matter (SOM). Phenolic and carboxylic groups, N-heterocyclic compounds, and lignin decomposition products were tentatively assigned as preferred binding sites using statistical analysis of pyrolysis-mass spectra and adsorption coefficients. Adsorption of sulfonamides to mineral soil colloids was weaker and resulted in a stronger desorption from clay-size fractions. Moreover, steric accessibility of organic-mineral complexes in clay-size fractions was significantly reduced. With a quantitative structure-property relationship (QSPR) model, combining the organic carbon concentration, the sulfonamides' chromatographic capacity factor (k'), and nondissociated species concentration (CF(a)), distribution coefficients (K(d)) were estimated with a cross-validated regression coefficient Q(2) = 0.71. Modeling and molecular mechanics calculations of antibiotic-SOM complexes showed preferred site-specific sorption via hydrogen bonds and van der Waals interactions. Distinct chemical structural properties, such as aromaticity and van der Waals volumes, correlated with the sorption data.

Sorption of Sulfonamide Pharmaceutical Antibiotics on Whole Soils and Particle-Size Fractions

QuEChERS - Fundamentals, relevant improvements, applications and future trends.

Soil organic matter (SOM) as a solid or as a film at mineral surfaces affects wetting properties in unsaturated soil Soil organic matter mostly consists of a heterogeneous mixture of components with hydrophilic and hydrophobic functional groups This paper analyzes relations of SOM to soil wettability by considering functional group compositions of different soluble fractions Forest soil samples from two loamy sand Cambisol profiles (locations Chorin and Steigerwald) and from a Podzol (Waldstein) were used to obtain water [SOM(W)] and sodium pyrophosphate [SOM(PY)] soluble SOM fractions The hydrophobic (A) and hydrophilic (B) functional groups of bulk soil SOM and of the soluble fractions were evaluated using transmission Fourier-transform infrared (FT-IR) spectroscopy Advancing liquid-solid contact angles (CA) were determined by using the capillary rise method For soil organic carbon (SOC) contents 10 g kg -1  Although hydrophilic groups in FT-IR spectra of SOM(W), SOM(PY), and bulk soil dominated (ie, A/B ratios between 008 and 05), soil wettability was reduced (ie, CA between 88 and 52°) Soil specific relations between CA and A/B ratios could be obtained after introducing relatively soil type independent factors, G As exponential functions of the SOC/clay relation, the G-factors imitate the effectiveness of functional groups with respect to wettability The results suggest that in addition to SOC content, the SOM composition may improve explanations of soil wettability if the spatial orientation of SOM functional groups at the SOM-mineral surface in the presence of sorption sites and polyvalent cations is considered

Composition of Organic Matter Fractions for Explaining Wettability of Three Forest Soils

Pesticides are intensively used in agriculture, and much effort is expended to manage and reduce possible deleterious effects on the environment.The soil compartment has a major influence on the fate and behaviour of pesticides applied to crops preemergence or early postemergence or chemicals subject to washoff from crop surfaces. Once in the soil, pesticide molecules partition between the aqueous and solid phases, which affects many other aspects of their behaviour: sorption can be rate limiting to volatilization, bioavailability (and thus efficacy and biodegradation rate), and subsurface transport. Understanding the fate of a pesticide in soil is fundamental to the accurate assessment of its environmental behaviour and vital in ensuring the safe use of new and existing products. It is also necessary to develop and validate computer simulation models for use as predictive tools in future environmental fate assessments.

Adsorption of Ionisable Pesticides in Soils

Adsorption and desorption isotherms of the herbicides imazapyr, imazethapyr and imazaquin on a soil humic acid have been performed at pH 2.8 and 4.0 (below and above the pKa of the herbicides). At both pH, adsorption increased according to the lipophilic character of the molecules (imazapyr < imazethapyr ≪ imazaquin). The extent of adsorption was higher at pH 2.8 than at pH 4.0 because of the partial ionization of the carboxylic groups of both herbicides and humic acids at increasing pH. Desorption of imazapyr and imazethapyr was nearly complete at pH 4 and higher than 60% at pH 2.8 while desorption of imazaquin was 45 and 8% at pH 4 and 2.8, respectively. No differences between adsorption isotherms at 10°C and 25°C were observed a pH 4.0 indicating that adsorption involved very weak bonds while at pH 2.8, adsorption was higher at 10°C than at 25°C indicating an exothermic process. The isosteric enthalpy of adsorption of each herbicide was low (about − 1 kJoule mole−1) suggesting that low energetic bonds ...

Interaction of imidazolinone herbicides with soil humic acids. Experimental results and molecular modeling.

Humic acids (HA) are organic molecules with complex structure and function and variable properties. They are insoluble in strongly acid pH conditions. At present, it is not clear how much is the amount of HA in solution at the pH of natural soils nor are known the characteristics of the different soluble fractions and their possible association with the inorganic phase of soil. The scope of this work was to characterize the soluble and insoluble fractions obtained by acidifying Na humate solution at pH values 3, 5, and 7 and to compare these fractions with the HA obtained at pH 1. At each pH, the precipitate and the soluble fractions were separated and characterized by elemental analysis, total acidity and carboxylic group content, infrared, and 13C NMR and 1H NMR spectroscopy. The HA fraction insoluble at pH 1 had a high acid group content and aromaticity but a low content of O- and N-containing groups. At pH 3, a fraction with nearly the same characteristics was obtained. At pH 1 and pH 3, the inorganic phase bound to the insoluble humic material was largely constituted by clay minerals and some Al and Fe hydroxides. The soluble fractions at pH values 1 and 3 were very poor and they were composed of a silica gel-like phase associated with polar organic material rich in carboxylic and metal-carboxylate groups. At pH values 5 and 7, only a small fraction of the Na humates precipitated. The fractions remaining in the solution were mainly composed of organic material particularly rich in aromatic and aliphatic groups, while the inorganic phase contained phyllosilicates. The fractions insoluble at pH values 5 and 7 contained a large amount of inorganic material that consisted mainly of phyllosilicates. The soluble fractions obtained at pH values 5 and 7 represent the humic component that in environmental situations would be dissolved in the soil solution. Our findings could be very useful for a more detailed investigation into the way HA influence plant metabolism under environmental-like conditions, both as regards pH conditions and interaction with the mineral fraction.

/pdf/chemical-and-spectroscopic-characterization-of-insoluble-and-3sroplrucv.pdf

Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

Adsorption of the imidazolinone herbicides imazapyr, imazethapyr and imazaquin have been studied on two humic acids and on ten soils. On humic acids, adsorption was promoted by low pH values and was in the order imazapyr < imazethapyr < imazaquin corresponding to the increasing lipophilicity of the molecules, in agreement with the octanol‐water partition coefficient. On soils, the correlations between the Freundlich coefficient Kf of the isothermes and the soil characteristics provided evidence that for each herbicide studied, the soil components mainly involved in the process were organic matter, amorphous iron oxides and iron‐organic matter complexes. Adsorption was promoted by low pH values. However, the order of adsorption in soils was imazapyr ≍ imazaquin < imazethapyr though imazaquin exhibited the highest affinity for soil humic acids. An hypothesis for this behaviour could be that the big and rigid quinoline moiety of the imazaquin molecule does not allow it to reach the adsorption sites ...

Adsorption of the herbicides imazapyr, imazethapyr and imazaquin on soils and humic acids

Humic acids were extracted from two histosols, an andosol, an inceptisol, a rice field soil, and a sludge-amended cambisol and characterized by elemental analysis, acidic groups titration, E4/E6 determination, Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (13C NMR) spectroscop

Effect of the Chemical Composition of Soil Humic Acids on Their Viscosity, Surface Pressure, and Morphology

Forchlorfenuron, N-(2-chloro-4-pyridinyl)-N'-phenylurea, is a plant growth regulator used to increase the size of kiwifruit, apples, table grapes, and peaches and to promote increased yields of potatoes, rice, and wheat. This study reports the comparison of the performances of two extraction methods [Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) and SPE] and two analytical methods (LC-UV and a LC/MS/MS) when determining forchlorfenuron in apples, kiwis, and grapes. Both extraction methods gave recoveries of forchlorfenuron from fruits >70%. The QuEChERS method was cheaper, safer, and less time-consuming than the SPE method and can be recommended for routine analysis. The LOQ was 2 and 10 microg/kg for the LC/MS/MS and LC-UV analysis, respectively. The LOD was 1 and 5 microg/kg for the LC/MS/MS and LC-UV analysis, respectively. The sensitivity of the LC-UV analysis was adequate to measure residue levels five times lower than the maximum residue limit (MRL) of the product. The QuEChERS and SPE methods were applied to monitoring the persistence of forchlorfenuron in field-treated kiwis, and it was found that the residual concentration was already much lower than the MRL 7 days after treatment.

Determination of forchlorfenuron in fruits by solid phase or QuECHERS extraction and LC-UV or LC/MS/MS.

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