Shahamat U. Khan

Soil organic matter

Soil organic matter includes plant and animal residues at various stages of decomposition, ranging from fresh undecomposed materials through partially decomposed and short-lived products of decomposition to well-decomposed humus. Plant and animal residues contain sugars, celluloses, hemicelluloses, proteins, lignins, waxes, and lipids. When these materials are incorporated into soils, sugars, celluloses, and hemicelluloses, most proteins undergo rapid decomposition. With decomposition, the proportion of resistant compounds such as lignin gradually increases. Resistant decomposition products and newly synthesized substances accumulate in soil and form complexes with its mineral components. Humus is formed in the latter stage as a result of such continued decomposition, resynthesis, and complexation. Humus is a fairly stable substance and requires very long time, for example, centuries to millennia, to be completely decomposed. Most mineral soils contain less than 5 % by weight of soil organic matter (SOM), but this little quantity of SOM has tremendous biological significance. It provides food for microorganisms, stores nutrients, retains water, acts as mulch, and performs as a soil conditioner and aggregating agent. It makes the soil friable and fertile. Soil organic matter contributes significantly to the sequestration of carbon.

The retention of hydrophobic organic compounds by humic acid

Abstract A humic acid, extracted from the Ah horizon of a Black Chernozem soil was found to fix or strongly retain significant amounts of hydrophobic organic compounds. Only approximately 8 per cent of the total alkanes and fatty acids occurring in the humic acid could be removed by exhaustive extraction with organic solvents. Another 19 and 11 per cent of the two classes of compounds could be removed by organic solvents after methylation of the humic acid, but extraction of the bulk of these compounds required extensive chromatographic separations of the methylated humic acid. Alkanes and fatty acids were estimated to account for up to 0.34 and 0.47 per cent of the weight of the original humic acid, respectively. Other hydrophobic organic compounds extracted were dialkyl phthalates, some of which are toxic, and di-sec-butyl adipate, which were estimated to account for about 1 per cent of the initial weight of the humic acid. The organic esters were shown not to be artifacts but are considered to be of biosynthetic origin. The data reported herein show that 100 g of humic acid can firmly retain up to 2 g, and possibly more, of hydrophobic organic compounds by a mechanism that most likely involves adsorption on external surfaces and in internal voids of a molecular sieve-type structural arrangement. The adsorption behaviour of humic substances for organic compounds, some of which may be toxic pollutants, should be of interest to those concerned with environmental and geochemical problems.

Adsorption kinetics, isotherms and thermodynamics of atrazine on surface oxidized multiwalled carbon nanotubes

The adsorption kinetics, isotherms and thermodynamic of atrazine on multiwalled carbon nanotubes (MWCNTs) containing 0.85%, 2.16%, and 7.07% oxygen was studied. Kinetic analyses were performed using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The regression results showed that the pseudo-second-order law fit the adsorption kinetics. The calculated thermodynamic parameters indicated that adsorption of atrazine on MWCNTs was spontaneous and exothermic. Standard free energy (DeltaG(0)) became less negative when the oxygen content of MWCNTs increased from 0.85% to 7.07% which is consistent with the low adsorption affinity of MWCNTs for atrazine.

Immobilization of pentachlorophenol in soil using carbonaceous material amendments.

In this study, three pentachlorophenol (PCP) laboratory-spiked and one field-contaminated soil were amended with 2.0% char, humic acid (HA) and peat, respectively. The amended soils were aged for either 7 or 250 days. After amendment, CaCl(2) extractability of PCP was significantly decreased. Desorption kinetics indicated that the proposed amendment could lead to a strong binding and slow desorption of PCP in soils. Amendment with char reduced the bioaccumulation factor (BAF) of PCP most significantly for earthworms (Eisenia fetida) in all soils studied. The results of both physicochemical and biological tests suggested that amendment reduced PCP bioavailability quickly and enduringly, implying that carbonaceous material amendment, especially char amendment, was a potentially attractive in situ remediation method for sequestration of PCP in contaminated soil.

Conversion of polycyclic aromatic hydrocarbons by Sphingomonas sp. VKM B-2434

A versatile bacterial strain able to convert polycyclic aromatic hydrocarbons (PAHs) was isolated, and a conversion by the isolate of both individual substances and PAH mixtures was investigated. The strain belonged to the Sphingomonas genus as determined on the basis of 16S rRNA analysis and was designated as VKM B-2434. The strain used naphthalene, acenaphthene, phenanthrene, anthracene and fluoranthene as a sole source of carbon and energy, and cometabolically oxidized fluorene, pyrene, benz[a]anthracene, chrysene and benzo[a]pyrene. Acenaphthene and fluoranthene were degraded by the strain via naphthalene-1,8-dicarboxylic acid and 3-hydroxyphthalic acid. Conversion of most other PAHs was confined to the cleavage of only one aromatic ring. The major oxidation products of naphthalene, phenanthrene, anthracene, chrysene, and benzo[a]pyrene were identified as salicylic acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, o-hydroxyphenanthroic acid and o-hydroxypyrenoic acid, respectively. Fluorene and pyrene were oxidized mainly to hydroxyfluorenone and dihydroxydihydropyrene, respectively. Oxidation of phenanthrene and anthracene to the corresponding hydroxynaphthoic acids occurred quantitatively. The strain converted phenanthrene, anthracene, fluoranthene and carbazole of coal-tar-pitch extract.

Rapid estimation of sulfide in rumen and blood with a sulfide-specific ion electrode☆

Abstract Free sulfide in rumen preserved with a sulfide antioxidation reducing buffer (SAOB) is determined directly and rapidly with a sulfide ion electrode using a standard addition technique. Acid-labile sulfide in blood preserved in alkaline cadmium acetate is determined by electrode measurement after acid liberation in a Johnson-Nishita apparatus and absorption in 50% SAOB. The sulfide antioxidant reducing buffer SAOB is not recommended for preservation of blood samples because of its desulfuration effect on S-proteins and S-amino acids present in blood.

UV irradiation of atrazine in aqueous fulvic acid solution

Abstract The photochemical stability to ultraviolet (UV) radiation of atrazine in aqueous solution was greater in the presence of fulvic acid than in its absence. The half‐life of atrazine in aqueous fulvic acid solution was greater at low than at high pH. The photolysis followed first order kinetics with respect to herbicide concentrations. The photolysis of atrazine in water yielded the 2‐hydroxy analogue only, but when the herbicide was treated similarly in the presence of a 0.01 percent fulvic acid solution, three N‐dealkylated products were also formed.

Release of soil bound (nonextractable) residues by various physiological groups of microorganisms

Soil bound 14C-labeled residues were released by four different physiological groups of microorganisms from an organic soil treated with 14C-ring-labeled prometryn [2-(methylthio)-4,6-bis(isopropylamino)-s-triazine]. The extent to which the different microbial populations released bound 14C residues (25-30% of the total bound 14C) from the gamma-irradiated soil after 28 days incubation did not differ considerably. Analysis of the extractable material from the incubated soil showed the presence of small amounts of the parent compound, and its hydroxy and mono-N-dealkylated analogues. Low level of 14CO2 (1.5-3.0% of the total bound 14C) was evolved from the microbial systems indicating ring cleavage of the released material as being a very minor reaction.

Permanganate oxidation of humic acids extracted from a gray wooded soil under different cropping systems and fertilizer treatments

Abstract Long-term effects of two cropping systems and of manure, fertilizer and lime treatments on products resulting from the permanganate oxidation of humic acids extracted from a gray wooded soil were investigated. The major oxidation products were benzenecarboxylic and phenolic acids. Humic acids extracted from soils under a 5-year rotation of grains and legumes yielded, per unit weight, more benzenecarboxylic acids than did those originating from soils under a wheat-fallow sequence. By contrast, the type of cropping system did not seem to affect the yields of phenolic acids. The application of lime and manure tended to reduce the yields of benzenecarboxylic and phenolic acids, suggesting that these treatments degraded the “cores” or more resistant chemical structures of humic acids. Other useful indexes of the relative molecular complexities of the humic acids were the total yields of oxidation products. These, regardless of rotation, were highest for the check plots and lowest for the plots treated with lime. Between 75 and 90% of the oxidation products were identified. The data show that the type of rotation, and especially the application of lime and manure, have significant effects on the synthesis and degradation of humic acid “nuclei”. These effects may be brought about by increased microbial activity and/or by chemical means. Permanganate oxidation may thus serve as a guide for assessing the degree of humification of soil humic acids.

Determination of paraquat residues in food crops by gas chromatography

SummaryA method is described for determining paraquat residues in lettuce, carrots and onions. The procedure is based on the extraction of the sample with 5N H2SO4 and catalytic hydrogenation of the acid extract. This is followed by column cleanup on alumina and subsequent determination by gas chromatography. Recoveries of paraquat added to lettuce, carrots and onion at 0.5, 0.1, and 0.05 ppm were between 75 to 86%, with maximum standard error of 4%. The lower limit of this method is in the 0.05 ppm range.