Maria D.R. Pizzigallo

Effects of conventional tillage on biochemical properties of soils

Abstract Modification of soil environment by different farming practices can significantly affect crop growth. Tillage causes soil disturbance, altering the vertical distribution of soil organic matter and plant nutrient supplies in the soil surface, and it may affect the enzyme activity and microbial biomass which are responsible for transformation and cycling of organic matter and plant nutrients. In this study, the influence of three conventional tillage systems (shallow plowing, deep plowing and scarification) at different depths on the distribution and activity of enzymes, microbial biomass and nucleic acids in a cropped soil was investigated. Analysis of variance for depth and tillage showed the influence of the different tillage practices on the activity of some enzymes and on the nucleic acids. Glucosidase, galactosidase, nitrate reductase and dehydrogenase activity were significantly affected by the three tillage modalities. Activity in the upper layer (0–20 cm) was higher in the plots tilled by shallow plowing and scarification than in those tilled by deep plowing. Positive relationships were observed between the soil enzymes themselves, with the exception of urease and pyrophosphatase activity. Moreover, significant correlations were found between DNA and β-galactosidase, and between RNA and β-glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase. α-Glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase were highly correlated with biomass C determined by the fumigation-extraction method.

Fractionation of sugar beet pulp into pectin, cellulose, and arabinose by arabinases combined with ultrafiltration

Incubation of beet pulp with two arabinases (alpha-L-arabinofuranosidase and endo-arabinase), used singularly or in combination at different units of activity per gram of beet pulp, caused the hydrolysis of arabinan, which produced a hydrolyzate consisting mainly of arabinose. Pectin and a residue enriched with cellulose were subsequently separated from the incubation mixture. The best enzymatic hydrolysis results were obtained when 100 U/g of beet pulp of each enzyme worked synergistically with yields of 100% arabinose and 91.7% pectin. These yields were higher than those obtained with traditional chemical hydrolysis. The pectin fraction showed a low content of neutral sugar content and the cellulose residue contained only a small amount of pentoses. Semicontinuous hydrolysis with enzyme recycling in an ultrafiltration unit was also carried out to separate arabinose, pectin, and cellulose from beet pulp in 7 cycles of hydrolysis followed by ultrafiltration. The yields of separation were similar to those obtained in batch experiments, with an enzyme consumption reduced by 3.5 times and some significant advantages over batch processes.

Molecular approaches to investigate herbicide-induced bacterial community changes in soil microcosms

Abstract. Since biochemical and microbiological methods used to study microbial community changes induced by anthropogenic activities can be biased, the impact of two herbicides on soil microorganisms was investigated by culture-independent molecular techniques. The effect of three different amounts (the recommended field dose, tenfold, and 100-fold the dose) of propanil or prometryne on the bacterial community of a clay soil, two modalities of incubation (soil moisture at 70% of the field capacity and a soil-herbicide suspension, 1:10, w:v), and time of incubation were investigated by denaturing gradient gel electrophoresis (DGGE) and amplified rDNA restriction analysis (ARDRA). Two sets of primers for 16S rDNA were used to amplify total soil DNA. Sterile and non-sterile samples were used to determine, by HPLC, the amounts of herbicides adsorbed on soil and transformed by soil microorganisms. Prometryne persisted in soil longer than propanil. Propanil was removed significantly more by non-sterile than by sterile samples, while for prometryne, slight differences were observed. 3,4-Dichloroaniline, a product of propanil hydrolysis, was detected in non-sterile samples and increased with incubation time. Propanil did not affect soil bacteria significantly as indicated by DGGE and ARDRA, with the only exception being the soil-herbicide suspension. Despite a lower utilization of prometryne by soil microorganisms, DGGE analysis showed a more diverse banding than with propanil. Some bands were also detected in the DNA sample extracted from the soil-prometryne suspension, and could be representative of bacterial species utilizing the herbicide as a carbon source, in two very different soil microcosms.

Mechanochemical degradation of pentachlorophenol onto birnessite

The existence of a lot of worldwide pentachlorophenol-contaminated sites has induced scientists to concentrate their effort in finding ways to degrade it. Therefore, an effective tool to decompose it from soil mixtures is needed. In this work the efficiency of the phyllomanganate birnessite (KBi) in degrading pentachlorophenol (PCP) through mechanochemical treatments was investigated. To this purpose, a synthesized birnessite and the pollutant were ground together in a high energy mill. The ground KBi-PCP mixtures and the liquid extracts were analyzed to demonstrate that mechanochemical treatments are more efficient in removing PCP than a simple contact between the synthesized birnessite and the pollutant, both in terms of time and extent. The mechanochemically induced PCP degradation mainly occurs through the formation of a surface monodentate inner-sphere complex between the phenolic group of the organic molecules and the structural Mn(IV). This is indicated by the changes induced in birnessite MnO(6) layers as a consequence of the prolonged milling with the pollutant. This mechanism includes the Mn(IV) reduction, the consequent formation of Mn(III) and new vacancies, and free Mn(2+) ions release. The PCP degradation extent is limited by the presence of chloro-substituents on the aromatic ring.

Effect of aging on catalytic properties in mechanochemical degradation of pentachlorophenol by birnessite.

Mechanochemistry, a technique concerning with milling contaminated samples for prolonged times, induces massive degradation of pollutants by grinding them in ball mills with different soil components or additives. In the present study, laboratory experiments were conducted to evaluate the effect of aging on the mechanochemical efficiency of the Mn-oxide birnessite in degrading pentachlorophenol (PCP). A comparative study on an aged birnessite (KBiA), used after 3years from synthesis, and a fresh birnessite (KBiF), employed immediately after synthesis, was carried out. The differences between the two birnessites, evidenced by spectroscopic and diffractometric techniques, are mainly relative to reduction of the Mn(IV) centered at the MnO₆ octahedra layers from the birnessite structure, which represent the most reactive sites for PCP degradation. The long term air drying at room temperature, by favouring reduction of Mn(IV) to Mn(III), produces an inorganic substrate that offers paucity of the less reactive sites for PCP degradation, thus reducing the oxidative potential of the KBiA. Accordingly, the more reactive fresh birnessite was employed in the experiment with a polluted soil. Adding a small amount of KBiF to soil only induces a light increase in PCP removal, probably due to the mechanically induced PCP adsorption and transformation onto clay minerals present in the soil. Besides, adding a higher dose of birnessite causes a stronger degradation of PCP.

Mechanochemical transformation of an organic ligand on mineral surfaces: the efficiency of birnessite in catechol degradation.

The aim of this work is to investigate the efficiency of the phyllomanganate birnessite in degrading catechol after mechanochemical treatments. A synthesized birnessite and the organic molecule were grounded together in a high energy mill and the xenobiotic-mineral surface reactions induced by the grinding treatment have been investigated by means of X-ray powder diffraction, X-ray fluorescence, thermal analysis and spectroscopic techniques as well as high-performance liquid chromatography and voltammetric techniques. If compared to the simple contact between the birnessite and the organic molecule, mechanochemical treatments have revealed to be highly efficient in degrading catechol molecules, in terms both of time and extent. Due to the two phenolic groups of catechol and the small steric hindrance of the molecule, the extent of the mechanochemically induced degradation of catechol onto birnessite surfaces is quite high. The degradation mechanism mainly occurs via a redox reaction. It implies the formation of a surface bidentate inner-sphere complex between the phenolic group of the organic molecules and the Mn(IV) from the birnessite structure. Structural changes occur on the MnO(6) layers of birnessite as due to the mechanically induced surface reactions: reduction of Mn(IV), consequent formation of Mn(III) and new vacancies, and free Mn(2+) ions production.

SEQUESTRATION OF CATECHOL AND PENTACHLOROPHENOL BY MECHANOCHEMICALLY TREATED KAOLINITE

The pollution of soils by organic contaminants, such as phenols, is a serious problem because of the high toxicity and persistence in the environment. Mechanochemical treatments (MTs) of polluted soils with minerals, such as clays and oxides, which have surfaces that exhibit catalytic properties, have been suggested to be a new useful strategy to promote both organic and inorganic pollutant degradation. Nevertheless, much still remains to be studied about the capability of clays to promote pollutant removal by means of the mechanochemical activation of the mineral surfaces. This work investigates the efficiency of the mineral kaolinite in promoting the sequestration of catechol (CAT) and pentachlorophenol (PCP) by MT. A well crystallized kaolinite (KGa-1b) was milled for prolonged times with different amounts of organic molecules so as to obtain two different clay:organic compound ratios. Prolonged grinding and a higher clay mineral:organic compound ratio were found to be more effective in promoting a stronger removal than simple contact. After 1 h of mechanochemical treatment, the PCP and CAT removal percentages were 32% and 20%, respectively. Additionally, a 7-day undisturbed incubation of the milled mixtures produced a trend for increased CAT removal (up to 40%). The interaction mechanism between kaolinite and each organic compound (i.e. CAT and PCP) after a MT was inferred by integrating information from spectroscopic, diffractometric, and chromatographic analyses. X-ray diffraction and Fourier-transform infrared data suggested a strong interaction between CAT and KGa-1b. This interaction mechanism likely occurs through the formation of an inner-sphere complex by H-bonding between the organic molecules and the oxygens of the kaolinite tetrahedral sheet. On the other hand, a weak interaction (i.e. van der Waals type) can occur between the KGa-1b O-planes and the PCP molecules, which likely bind to the external surfaces of KGa-1b.