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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the fall of 2000, 34 groundwater samples were collected from beneath an active pesticide reformulating and packaging facility in coastal northeastern Florida to measure the enantiomer fractions (EFs) of alpha-hexachlorocyclohexane (alpha-HCH) as an indicator of biodegradation of this chlorinated pesticide in groundwater. Concentrations of alpha-HCH as high as 500 microg/L were observed beneath the historical source area and decreased with distance downgradient. Seventy-eight percent of the EF values were greater than 0.504 and ranged up to 0.890, indicating that the (-)-alpha-HCH enantiomer is preferentially degraded relative to the (+)-alpha-HCH enantiomer at this site. Samples taken from the groundwater that flows north from the historical disposal facility to a local discharge point at a creek did not indicate enantioselective degradation (EF values ranged from 0.495 to 0.512). The acidity (pH 3.7-4.6) and short flow path to the creek for this lobe of the groundwater plume likely preclude biodegradation of alpha-HCH. In contrast, the neutral lobe of the groundwater plume, which flows eastward from the historical source area, demonstrated enantioselective degradation (EF values ranged from 0.500 to 0.890 and increased with distance from the source area). Groundwater conditions beneath this portion of the site are conducive to biodegradation of HCH owing to anaerobic reducing conditions and lengthy travel times, and the chiral signatures for alpha-HCH provide evidence that biological degradation is occurring beneath this portion of the site.
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PMID:Evidence of enantioselective degradation of alpha-hexachlorocyclohexane in groundwater. 1507 68

Heterogeneous photocatalytic degradation of gamma-HCH on soil surfaces was carried out to evaluate the photocatalytic effectiveness of alpha-Fe2O3 and TiO2 toward degrading gamma-HCH on soil surfaces. After being spiked with gamma-HCH, soil samples were loaded with alpha-Fe2O3 or TiO2 and exposed to UV-light irradiation. Different catalyst loads, 0%, 2%, 5%, 7%, and 10% (wt.) alpha-Fe2O3; 0%, 0.5%, 1%, 2: (wt.)TiO2, were tested for up to 7 d irradiation. The effects of soil thickness, acidity, and humic substances were also investigated. The obtained results indicated that the gamma-HCH photodegradation follows the pseudo-first-order kinetics. The addition of alpha-Fe2O3 or TiO2 accelerates the photodegradation of gamma-HCH, while the photodegradation rate decreases when the content of alpha-Fe2O3 exceeds 7% (wt.). The degradation rate increases with the soil pH value. Humic substances inhibit the photocatalytic degradation of gamma-HCH. Pentachlorocyclohexene, tetrachlorocyclohexene, and trichlorobenzene are detected as photodegradation intermediates, which are gradually degraded with the photodegradation evolution.
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PMID:Photocatalytic remediation of gamma-HCH contaminated soil induced by alpha-Fe2O3 and TiO2. 1590 Jul 24

The acids under study differed from one another in length of the carbon chain [N + H(3)(CH(2))(n)PO(3)H(-) for n = 1, 2, 3], substitution on the nitrogen atom [R(1)R(2)N + HCH(2)PO(3)H(-) for R(1) = H; R(2) = Me, Et and R(1) = R(2)= Me, Et] or extent of branching on the carbon atom adjacent to functional groups [N + H(3)CR(3)R(4)PO(3)H(-) for R(3) = H; R(4) = Me, Et, nPr, iPr, nBu and R(3) = R(4) = Me]. Acidity constants and overall stability constants of complexes formed with Ca(II), Mg(II), Co(II), Ni(II), Cu(II), Zn(II) were obtained with the multiparametric refinement programs MUPROT and MUCOMP, applied to potentiometric data, obtained at 25 degrees , in a 0.1M potassium nitrate medium. In the most general case, the existing species are MHA(+), MA, M(OH)A(-), MH(2)A(2), MHA(-)(2) and MA(2-)(2), where A(2-) stands for the fully ionized ligand; preliminary examination of results points out some predominant microscopic forms.
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PMID:[Acidites et complexes des acides (alkyl-et aminoalkyl-) phosphoniques-IV: acides aminoalkylphosphoniques R(1)R(2)N(CH(2))(n)CR(3)R(4)PO(3)H(2)]. 1896 90