Protease, a common extracellular enzyme in soils, was adsorbed onto smectite and bentonite clays exchanged with both Na and Ca cations. Initial concentrations and residual activity of the enzyme were ...studied together with a new approach to adsorption modeling and an introduction to the technique of phase plane analysis. Protease adsorption reached a maximum level of 0.34 mg mg-1 on the Na-exchanged smectite and a minimum of 0.20 mg mg-1 on the Ca-exchanged bentonite. The inhibition study of protease activity within the clay matrix showed that the enzyme retained a maximum of 9.9% (Na-exchanged smectite) and a minimum of 0% (Ca-exchanged bentonite) of its original activity. As opposed to the classic Langmuir and Freundlich model description, a general form, the Langmuir−Freundlich isotherm in combination with phase plane analysis, was used. The model appeared to agree well with the adsorption data of all four of the enzyme/clay complexes. The use of phase plane analysis was shown to be a powerful tool in equilibrium and kinetic sorption relationships. Kinetic modeling was able to identify problems with our isotherms for higher initial concentrations of protease. For all initial concentrations, film diffusion effects contribute to limiting the overall rate of adsorption.
Heavy metals have been increasingly released into our environment. We present here, for the first time, the global industrial age production of Cd, Cu, Cr, Hg, Ni, Pb, and Zn, and their potential ...accumulation and environmental effects in the pedosphere. World soils have been seriously polluted by Pb and Cd and slightly by Zn. The potential industrial age anthropogenic Pb, Hg, and Cd inputs in the pedosphere are 9.6, 6.1, and 5.2 times those in the lithosphere, respectively. The potential anthropogenic heavy metal inputs in the pedosphere increased tremendously after the 1950s, especially for Cr and Ni. In 2000, the cumulative industrial age anthropogenic global production of Cd, Cr, Cu, Hg, Ni, Pb, and Zn was 1.1, 105, 451, 0.64, 36, 235, and 354 million tonnes, respectively. The global industrial age metal burdens per capita (in 2000) were 0.18, 17.3, 74.2, 0.10, 5.9, 38.6, and 58.2 kg for Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively. Acidification may increase the bioavailability and toxicity of heavy metals in the pedosphere. The improvement of industrial processing technology reducing the metal dispersion rate, the recycling of metal-containing outdated products, by-products and wastes, and the development of new substitute materials for heavy metals are possible strategies to minimize the effects of heavy metals on our environment.
ABSTRACT
Understanding pollutant sorption, bioremediation of these pollutants, and their interactions with humic substances requires knowledge of molecular‐level processes. New developments with ...nuclear magnetic resonance (NMR) experiments and labeled compounds have improved the overall understanding of these mechanisms. The advancements made with two‐dimensional NMR show great promise, as structural information and hydrogen–carbon bond connectivity can be discerned. This communication presents the application of improved two‐dimensional NMR methods, the double quantum filtered (DQF) correlation spectroscopy (COSY) and echo/anti‐echo heteronuclear single quantum coherence (HSQC) experiments, for use in structural studies of humic substances. Both experiments were found to produce significant improvements over the conventional COSY and heteronuclear multiple quantum coherence (HMQC) experiments that have been previously employed in similar studies. The more sensitive echo/anti‐echo HSQC experiment produced more cross‐peaks with higher resolution when compared with the HMQC spectra. The DQF‐COSY significantly suppressed the diagonal signals and allowed numerous signals previously hidden in the standard COSY experiment to be observed. These improvements will aid current characterization strategies of humic substances from soils, sediments, and water and their subsequent reactions with pollutants and microorganisms.
The effects of time of precipitation and soil type on runoff losses of cyanazine and metolachlor were studied using a tilted-bed, microplot system. Two silt loam soils, Bosket and Dubbs, and a ...Sharkey silty clay were evaluated. Rainfall (22 mm h−1) was simulated at 0, 2, and 14 days after treatment (DAT). Time of precipitation did not impact herbicide losses or any of the runoff parameters evaluated in this study. Water runoff occurred sooner and in greater quantities from the surfaces of Bosket and Dubbs silt loam soils than from the surface of Sharkey silty clay. Runoff losses of cyanazine did not vary by soil type. Soil drying produced large cracks in Sharkey silty clay, which greatly reduced runoff in this soil. Combined runoff and leachate losses were highest from Dubbs silt loam. Runoff losses of metolachlor were not affected by soil type. However, regression analyses indicated that time of precipitation and soil type interacted to affect initial metolachlor concentration. At 14 DAT, initial metolachlor concentration was highest in runoff from Sharkey soil. Time of precipitation ranked with respect to initial metolachlor concentration in runoff from Bosket and Dubbs silt loam soils were 0 > 2 > 14 DAT and 0 = 2 > 14 DAT, respectively. Nomenclature: Cyanazine; metolachlor.
Currently, less than 3% of the U.S. population lives on a farm (Riedel, 2006). Technological advances and mechanization coupled with other societal factors, have led to the decline of an ...agriculturally literate population (Kovar & Ball, 2013). Blair (2009) identified one strategy for increasing agricultural literacy as implementing education that promotes agricultural activities via experience. This quantitative study was conducted at three private schools in Mississippi during the spring of 2015. The primary investigator (PI) taught six (6) lessons contextualized in agriculture to tenth grade students enrolled in advanced biology courses. The study consisted of a control group (no instruction), and two experimental groups; one received direct instruction only, and one was led through various experiences relevant to plant science and agricultural production with a high-tunnel greenhouse. Pre and post-tests assessed knowledge gain. Participants’ knowledge scores increased significantly among experimental groups (p < .001). Multivariate analysis revealed post-test scores between experimental groups were significantly different (p = .016). Further analysis of the data displayed that 67% of the variance in scores was attributed to method of instruction and a strong correlation existed between post-test scores and treatment group (R = .820).
Here we show, for the first time, evidence of the primary molecular structures in humic substances (HS), the most abundant naturally occurring organic molecules on Earth, and their associations as ...mixtures in terrestrial systems. Multi-dimensional nuclear magnetic resonance (NMR) experiments show us that the major molecular structural components in the mixtures operationally defined as HS are aliphatic acids, ethers, esters and alcohols; aromatic lignin derived fragments; polysaccharides and polypeptides. By means of diffusion ordered spectroscopy, distinct diffusion coefficients consistent with relatively low molecular weight molecules were observed for all the components in the mixtures, and saccharides were the largest single class of component present. Liquid chromatography NMR confirmed that HS components can be easily separated and nuclear Overhauser effect (NOE) enhancements support the finding that the components are of relatively low molecular weight <~2,000 Da. The widely recognized properties of HS, i.e., characteristics indicative of crosslinked, macromolecular networks, can now be explained as aggregation of mixtures, most likely instigated by complexation with metal cations.
The preferential sorption of model compounds to calcium-exchanged montmorillonite surfaces was investigated using 1H high-resolution magic-angle spinning (HR-MAS) and liquid-state NMR. Synthetic ...mixtures, representing the major structural categories abundant in natural organic matter (NOM), and two soil extracts were sorbed to montmorillonite. The NMR spectra indicate that, of the organic components observable by 1H HR-MAS NMR, aliphatic components preferentially sorb to the clay surface, while carbohydrates and amino acids mainly remain in the supernatant. These results may help explain the highly aliphatic nature of organic matter associated with clay fractions in natural soils and sediments. Investigations using the synthetic mixtures demonstrate a specific interaction between the clay surface and the polar region in 1-palmitoyl-3-stearoyl-rac-glycerol. Similar observations were obtained with natural soil extracts. The results presented have important implications for understanding the role of organoclay complexes in natural processes, and provides preliminary evidence that HR-MAS NMR is a powerful analytical technique for the investigation of organoclay complex structure and conformation.
High resolution-magic angle spinning nuclear magnetic resonance (HR-MAS NMR) allows the application of solution-state NMR experiments to samples that are not fully soluble and contain solids. Only ...the species in contact with the solvent system employed become NMR observable. In this study utilizing D2O as the solvent system we show it is possible to examine the structures at the solid−aqueous interface of a whole soil. Combining one- and two-dimensional HR-MAS NMR allowed, for the first time, the identification of fatty acids, aliphatic esters, and ethers/alcohols as prominent species at the solid−aqueous interface of the soil with signals from sugars and amino acids also apparent. Few, if any signals from aromatic protons were observed when the soil was swollen in aqueous media, although these signals are observed in extracts from the same soil and when the soil is swollen with a more penetrating solvent (DMSO-d 6) which is known to disassociate hydrogen bonds. These findings indicate that the soil aromatic moieties are protected in hydrophobic regions which are not water accessible. Furthermore, when the soil was amended with a herbicide (trifluralin), direct observations of interactions between the protons on a xenobiotic and the surrounding soil matrix were possible for the first time. HR-MAS promises to be a method that can be widely applicable to a range of complex environmental samples without the need for extraction, pretreatment, or purification.
Urban soils are often not ideal planting sites due to removal of native topsoil or the mixing of topsoil and subsoil at the site. Adding pine bark based soil amendments to a clay soil altered soil ...bulk density and soil compaction which resulted in improved plant growth. Addition of nitrogen (N) or cotton gin waste to pine bark resulted in improved plant growth compared to pine bark alone. Growth of pansies (Viola x wittrockiana) during the 1999-2000 winter growing season was enhanced by the addition of pine bark plus nitrogen at 3- and 6-inch (7.6- and 15.2-cm) application rates (PBN3 and PBN6) and pine bark plus cotton gin waste at the 6 inch rate (CGW6). Plant size and flower production of vinca (Catharanthus roseus) were reduced by pine bark amendments applied at 3- or 6-inch rates (PB3 or PB6). Crapemyrtle (Lagerstroemia indica) grown in plots amended with 3 or 6 inches of pine bark plus cotton gin waste (CGW3 or CGW6) and pine bark plus nitrogen at 3- or 6-inch rates (PBN3 or PBN6) produced greater shoot growth than other amendment treatments. In some instances PB3 treatments suppressed growth. High levels of N and soluble salts derived from CGW and PBN soil amendments incorporated into the soil probably contributed to the improved plant growth observed in this experiment.
An adequate supply of Co in pasture is important to the health of grazing animals. Bio-availability of Co in soils is largely depended upon its distribution among solid-phase fractions. Distribution ...of cobalt in six arid-zone soils and its redistribution among the solid-phase fractions during long-term saturated paste incubation were studied. Cobalt was fractionated by a selective sequential dissolution procedure into six empirically defined fractions. Concentrations of total Co and Mn or Fe, and Co and Mn fractionation pattern were strongly correlated in the soils. During saturated incubation, Co in soils was redistributed mainly from the Mn oxide bound, and to some extent, Fe oxide bound and organic matter bound fractions into the carbonate bound fraction. During saturated incubation, significant correlations were found between concentrations of Co and Mn in the Mn oxide bound, Fe oxide bound and carbonate bound fractions. Also, significant correlations between concentrations of Co and Fe in the Fe oxide bound fraction were present. However, a negative correlation between concentrations of Co and Fe in the Mn oxide bound fraction was observed. The rates of redistribution of Co between these solid-phase components were initially high: major changes occurred in the first 3 days in the sandy soil and the first 18 days in the loessial soil. Afterwards, the rates of change slowed but changes in redistribution continued during the rest of the study period of one year.
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