Extractants degradation

Another lab study (102) using a loamy sand (pH 6.8) and a fine sand (pH 6.4) showed oxamyl half-lives of 11 and 15 days under aerobic conditions, respectively. There were no extract-able degradation products. However, under anaerobic conditions, a half-life of 6 days was found and extractable degradation products persisted (102). 

Extraction of U(VI) and Pu(IV) from 1 to 8 mol L 1 HN03 solutions by radiolytically degraded DCH18C6 in toluene was studied (256). A decrease in the distribution ratios for both U and Pu was observed for irradiation in the range 0.010-0.071 MGy, with a higher effect for Pu(IV). For 0.2 mol I. DCH18C6-toluene solution in contact with 3 mol I. nitric acid, D, decreased from 0.21 to 0.12 and /.)hl from 64.3 to 6.42 after a dose of 0.07 MGy. This behavior was explained by both diluent and extractant degradation. 

From such studies, it can be expected that progress will be made toward the prevention of extractant degradation and the design of more stable extractants. 

The effect of soil composition on the photolysis of soil-adsorbed niclosamide using a xenon lamp was reported [86]. The study was conducted with both moist and air-dried soils fortified with sodium nitrate (commonly used as a fertilizer), iron (a natural soil component) or humic acid. Degradation in soils fortified with iron was slower than in that in soils fortified with sodium nitrate and no extractable degradation products were observed in any of the soils fortified with humic acid. Soils with higher organic or iron contents or that are exposed to fertilizers do not affect as dramatically the half-life of pesticides as does the presence of moisture in the soil. The maintenance of moisture was found to be crucial to the reliability of soil photolysis studies. 

To determine the quantitative effects of this consolidation procedure, fabric disks cut from the extracted degraded fabric were used as substrates. These fabrics were torn on an Instron tensile testing machine as described earlier and patched with six applications of either the 0.1% dyed wood pulp or the 0.05% dyed Cellunier P slurry. The samples were then torn again on the Instron tester. The average breaking strengths and add-ons of the samples after six passes with slurry are reported in Table IV. A typical tom fabric and a patched fabric are shown in Figures 6 and 7. 

Phytoremediation can be placed in the bioremediation category as either an in situ or ex situ remediation technology, depending on the approach used. It uses plants and associated micro-organisms to extract, degrade, and stabilize PAHs. If the plants are used in place, the method is in situ. If the soil is excavated and taken to a greenhouse, then the method is classified as ex situ. 

Another case in point is the solvent extraction of lignins (Nimz, 1966). Are the propylbenzene oligomers found in the extract degradation products of the original lignin polymer, or are they precursors co-occurring with the polymer In any case, their identities have helped establish the structure of native lignin. 

Al-Malaika et al. [56-60] have extracted degradation products of a-toco-pherol, formed during the melt processing of PP, by Soxhlet extraction for a time of 6h with DCM. The concentrations of the different degradation products were calculated from the extinction coefficients in HPLC analysis in n-hexane [56]. The HPLC analysis in n-hexane was used to fractionate the extracts the fractions were then analyzed by UV, FTIR, H-NMR and MS. Several oxidation products (Scheme 6) were found quinonoids (I), trimers (V), dimers (III, IV) and aldehydes (II). 

RSD values for extracted degradation products, corrected with the respective internal standard, were calculated from six extractions made on the same day. 

The extracted degradation products were identified and quantified by a ThermoFinnigan GCQ (San Jose, CA, USA). The column used a wall-coated open tubular (WCOT) fused silica CP-WAX 58 (FFAP)-CB column from Varian (25 m x 0.32 mm id, od 0.2 pm). Helium of scientific grade purity from AGA (Stockholm, Sweden) was used as carrier gas at the constant velocity of 40 cm/s. The initial oven temperature was 40 "C, which was held for 1 minute. The oven was heated to 250 C for 15 minutes. Electron impact mode (El) detection was used with an electron energy of 70 eV. The mass-range scanned was 35-400 m/z and the ion source and transfer line temperatures were 180 and 250 C, respectively. The injector temperature was set to 250 C. A sample (1 pi) was injected in splitless injection mode and two blanks were run between each sample by injecting clean methanol (0.15 M HCl). 

Another reason for careful interpretation of the disk-diffusion assay is that it is subject to false-positive results that can be misinterpreted as antibiotic activity. For example, physical characteristics of the extract (viscosity, pH, etc.) can generate small zones of growth inhibition when bacteria are inoculated directly onto the surface of the agar plate. In addition, we have observed that some primary metabolites can inhibit growth when tested at high concentrations. It is also possible that simple molecules, or extract degradation products, can exhibit mild antibiotic properties. For these reasons, it is important that replicate extracts are tested and that small zones of inhibition are interpreted with caution. It is also important to clearly state the concentrations tested, even if naturally occurring concentrations are not known, so that activities can be reproduced and evaluated at a later time. 

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