Kinetic studies sediments

Weber EJ, Wolfe NL. 1986. Kinetic studies of aromatic azo compounds in anaerobic sediment/water systems abstract. In 191st National meeting American Chemical Society Division of Environmental Chemistry 26 239-40. 

In a second class of experiments, detailed studies of disappearance kinetics in sediment-water systems were performed. A series of centrifuge tubes was assembled containing identical concentrations of parent compound and identical sediment-to-water ratios. 

Neutral Hydrolysis Studies. Investigations of neutral (pH-independent) hydrolysis kinetics in sediment/water systems were conducted for three organophosphorothioate insecticides (chlorpyrifos, diazinon and Ronnel), 4-(p-chlorophenoxy)butyl bromide, benzyl chloride, and hexachlorocyclopentadiene. 

Alkaline Hydrolysis Studies. Alkaline catalyzed hydrolysis kinetics in sediment/water systems have been investigated for chlorpyrifos and the methyl and n-octyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D). 

Chlorpyrifos. As was the case for the neutral hydrolysis studies, the most detailed kinetic investigations of alkaline hydrolysis kinetics in sediment/water systems have been conducted using chlorpyrifos (10). As can be seen from Figure 2, alkaline hydrolysis of chlorpyrifos is not second-order, so the value selected for k cannot be calculated from the pH and a second-order rate constant. Nevertheless, since aqueous kinetics at alkaline pH s for chlorpyrifos was always pseudo-first order, careful pH measurements and Figure 2 can be used to select accurate values for k at any pH. 

Kinetic studies in sediment/water systems with Direct Red 2, Acid Black 92, Acid Red 4, Acid Red 18, and Direct Yellow 1 lead to linear and biphasic plots of dye loss over time. For all but Direct Yellow I, dye loss was usually preceded by a lag or adaptation phase. Acid Black 92 and Direct Red 2 were transformed completely in less than 24 and 48 hours, respectively, but Acid Yellow 151 and Direct Yellow 1 showed half-lives of greater than 2 years. The rapid initial drop in concentration of all dyes observed, with the exception of Acid Red 18, was presumed to be due to sorption. Tests to determine the effect of pH on... 

The Michael addition mechanism, whereby sulfur nucleophiles react with organic molecules containing activated unsaturated bonds, is probably a major pathway for organosulfur formation in marine sediments. In reducing sediments, where environmental factors can result in incomplete oxidation of sulfide (e.g. intertidal sediments), bisulfide (HS ) as well as polysulfide ions (S 2 ) are probably the major sulnir nucleophiles. Kinetic studies of reactions of these nucleophiles with simple molecules containing activated unsaturated bonds (acrylic acid, acrylonitrile) indicate that polysulfide ions are more reactive than bisulfide. These results are in agreement with some previous studies (30) as well as frontier molecular orbital considerations. Studies on pH variation indicate that the speciation of reactants influences reaction rates. In seawater medium, which resembles pore water constitution, acrylic acid reacts with HS at a lower rate relative to acrylonitrile because of the reduced electrophilicity of the acrylate ion at seawater pH. 

Sedimentation field-flow fractionation was used also for the kinetic study of hydroxyapatite (HAP) particles aggregation in the presence of various electrolytes to determine the rate constants for the bimol-ecular process of aggregation and to investigate the possible aggregation mechanisms describing the experimental data. The HAP sample contained polydis-perse, irregular colloidal particles with number-average diameter dys = 0.262 + 0.046 /rm. 

Polyacrylic acid was purchased from Polysciences, Inc., and used with no further purification. HA was obtained from lake sediments (Lake Bradford, FL), and isolated and purified as described earlier (72). Two different size fractions of HA were obtained by ultrafiltration, as described below. All kinetic studies were performed at 0.10 M ionic strength (adjusted by the addition of NaC104), and were buffered by the addition of acetate (acetic acid and sodium acetate, pH 4.2). Buffer concentrations were 0.01 M. TES (N-tris[hydroxymethyl]methyl-2-aminoethane sulfonic acid, pH 7.0) buffer was used to maintain hydrogen ion concentrations during humate fractionation. 

Van Cappellen and Q.iu (1997b) used flow-through reactor studies to demonstrate that the dissolution rate of unaltered Si-rich sediment from the Southern Ocean follows a rate law that is exponential rather than linear with respect to the degree of undersaturation. The implication is that the rate of dissolution is much greater near the sediment-water interface than below. In fact they find that, when the laboratoiy kinetic studies are applied to the sediments, Si02 dissolution is pretty much finished below depths of a few centimeters. The question remains as to what processes cause the kinetics of opal... 

Weber, E. J., and N. L. Wolfe (1987), Kinetic Studies of the Reduction of Aromatic Azo Compounds in Anaerobic Sediment/Water Systems, Environ. Toxicol. Chem. 6, 911 919. 

Kinetic experiments with synthetic iron oxyhydroxides have shown that the initial microbial reduction rate increases with increasing initial ferric iron concentration up to a given maximum reduction rate (Bonneville et al. 2004). This observation was explained by a saturation of active membrane sites with Fe(III) centers. The respective reaction was best described with a Michaelis-Menten rate expression with the maximum reduction rate per cell positively correlating with the solubility of the iron oxyhydroxides (Bonneville et al. 2004). Kinetic studies involving iron are not only inherently important to describe reaction pathways and to derive rate constants, which can be used in models. Kinetic studies also increasingly focus on iron isotopic fractionation to better understand the iron isotopic composition of ancient sediments, which may assist in the reconstruction of paleo-environments. Importantly, iron isotope fractionation occurs in abiotic and biotic processes the degree of isotopic fractionation depends on individual reaction rates and the environmental conditions, e.g. whether reactions take place within an open or closed system (Johnson et al. 2004). 

Ceremigna D, Polettini A, Pomi R, Rohe E, De Propris L, Gabellini M, Tomato A. (2006). A kinetic study of chelant-assisted remediation of contaminated dredged sediment. Journal of Hazardous Material 137 1458-1465. 

Wu YG, Hui L, Li X, Zhang YZ, Zhang WC (2007) Degradation of aniline in weihe riverbed sediments under denitrification conditions. J Environ Sci Health, Part A Tox Hazard Subst Environ Eng 42(4) 413-419. doi org/10.1080/10934520601187302 Yadav S, Tyagi DK, Yadav OP (2011) EquiUbrium and kinetics studies on adsorption of aniline blue from aqueous solution onto rice husk carbon. Int J Chem Res 2(3) 59-64 Yang J, Tsai FP (2001) Development of a solid-phase microextraction/reflection-absorption infrared spectroscopic method for the detection of chlorinated aromatic amines in aqueous solutions. Anal Sci 17 751-756... 

Like the other glycosyltransferases, this enzyme was essentially particulate, and 85% of the activity sedimented at 300,000 g. Kinetic studies with 3-0-/3-D-gaiactosyl-D-galactose as substrate (see below) showed that the glucuronosyltransferase was active over a wide pH range, the activity being almost equal between pH 5 and 8. Like the galactosyltransferases, the enzyme was stimulated by Mn+ +, with maximal activity att ed at a concentration of 15 mA/. 

Electro-Kinetic Effects. The appHcation of d-c potential in filtration or sedimentation is known to have a beneficial effect on the separation. Although this has been known and studied since the beginning of the nineteenth century, practical appHcation and development have only accelerated since the late 1980s commercial appHcation is likely. 

Although the results of experiments on the dechlorination of pentachlorophenol (Bryant et al. 1991) enabled elucidation of the pathways to be elucidated, this study also revealed one of the limitations in the use of such procedures. Detailed interpretation of the kinetics of pentachlorophenol degradation using dichlorophenol-adapted cultures was equivocal due to carryover of phenol from the sediment slurries. 

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