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Query: UMLS:C1835664 (TOC)
 2,763 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fluka humic acid used as a model substrate in these studies was analysed for elemental and the oxygen-containing functional groups. It was chlorinated at C:Cl molar ratios of 1:1 and 1:0.3 and subsequently separated into molecular weight fractions by ultrafiltration. The freeze-dried, chlorinated humic acid and the respective molecular weight fractions were analyzed for TOC, TOX, alkylating activity using 4-(p-nitrobenzyl)pyridine and mutagenicity by the Ames/Salmonella/microsome assay with strains TA-98 and TA-100. Results indicated that predominantly non-volatile, direct-acting mutagenic and/or alkylating agents were formed during humic acid chlorination and that these agents were unevenly distributed among the various molecular weight fractions. Formation of mutagenic and alkylating agents were highly dependent upon level of chlorination and total organic carbon. Higher levels of mutagenic and alkylating activities were produced with increasing concentration of chlorine in the range of 0.4-1.2 chlorine equivalents per mole of carbon. However, both these activities in the freeze-dried, chlorinated humic acid solutions containing the non-volatiles or the fresh solutions decreased gradually with increasing pH and storage time, apparently due to degradation and hydrolysis of some of the components.
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PMID:Mutagenicity and alkylating activity of the aqueous chlorination products of humic acid and their molecular weight fractions. 252 78

Technical development work is presented, where the VUV photochemically induced oxidative degradation is used: (i) for analytic purposes, and (ii) for small to medium scale (< 10 m2/d) waste water treatment processes or ultrapure water production. In the first case, small Xe-excimer radiation sources with an integrated reaction space designed for optimal conditions, as far as incident photon flux density, turbulence and concentration of dissolved molecular oxygen are concerned, have been built and tested. Under conditions of exhaustive oxidation and/or mineralization of pollutants in a continuous regime, they may be used for sample pre-treatment modules prior TOC, TOX and electrochemical trace metal analysis. Under conditions of partial oxidation or mineralization, the same lamp/reactor combination may be used for functionalization purposes prior to e.g. GC or HPLC analyses. In the second case, mass transfer limitations between the non-irradiated bulk volume and the irradiated volume are overcome by the electrochemical generation of molecular oxygen within or close to the irradiated volume and by the design of the photochemical part of the reactor.
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PMID:Technical development of UV-C- and VUV-photochemically induced oxidative degradation processes. 1507 77

The reductive degradation of a chlorinated herbicide by iron powder was investigated at lab scale. The studied substrate was triallate (S-2,3,3-trichloroallyl di-isopropyl thiocarbamate) which contains a trichloroethylene moiety potentially reducible by zero-valent iron. Degradation reactions were carried out in batch, at 25 degrees C, in the absence of oxygen, by contacting electrolytic iron powder (size range: 20-50 microm) with a triallate aqueous solution (2.5 mgl(-1)). Herbicide decay, corresponding evolutions of TOC, TOX and chloride ion release were regularly monitored throughout the reactions. Furthermore, the main degradation by-products were identified by HPLC/MS. The results showed that, after 5 days, herbicide degradation extent was about 97% and that the reaction proceeded through the formation of a dechlorinated alkyne by-product (S-2-propinyl di-isopropyl thiocarbamate) resulting from the complete dechlorination of triallate. The subsequent reduction of such an alkyne intermediate gave S-allyl di-isopropyl thiocarbamate as main end by-product. The identified by-products suggested that dechlorination took place mainly via reductive beta-elimination. However, as traces of dichloroallyl di-isopropyl thiocarbamate were also detected, a role, although minor, was assigned even to hydrogenolysis in the overall dechlorination process.
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PMID:Chlorinated herbicide (triallate) dehalogenation by iron powder. 1548 19

With the aim to evaluate the effect of temperature, 4-chloro-3-methyl phenol (CMP) degradation by Fenton's reagent was investigated at 25 and 70 degrees C under the following initial conditions: [CMP]0 = 10 mM, [Fe2+]0 = 0.5 mM; ([H2O2]0/[CMP]0) = 80, pH0 = 3. The results indicated that CMP degradation was strongly influenced by temperature. In fact, the maximum TOC removal, achieved after ca. 24h, was by far greater at 70 degrees C (85%) than at 25 degrees C (36%). The same happened for organic chlorine (TOX) conversion into inorganic chloride, i.e. 100%, after 3 h at 70 degrees C, and 87%, after 27 h at 25 degrees C. As the recorded trends of CMP removal and chloride formation were basically the same, hydroxy substitution (ipso-substitution) was hypothesised as one likely mechanism of CMP degradation. The higher level of mineralization recorded at 70 degrees C was ascribed to: (i) a greater *OH concentration; (ii) a consequently greater extent of CMP oxidation to organic acids; (iii) a higher decarboxylation rate of such acids. An interesting consequence of such extended organic acids decarboxylation was a pH increase up to 8 that, in turn, caused, in the treated mixture, the decomposition of excess H2O2 as well as the precipitation of iron ions. These two latter outcomes are technologically important considering that usually, before discharging Fenton treated wastewater, specific polishing steps are required just to remove iron ions, decompose excess hydrogen peroxide and neutralise the pH.
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PMID:Temperature activated degradation (mineralization) of 4-chloro-3-methyl phenol by Fenton's reagent. 1576 92