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ASCORBIC ACID REDUCTION OF RESIDUAL ACTIVE CHLORINE IN POTABLE WATER PRIOR TO HALOCARBOXYLATE DETERMINATION
JOURNAL OF ENVIRONMENTAL MONITORING 2 (3): 253-256 2000
Urbansky ET, Freeman DM, Rubio FJ
US EPA, Off Res & Dev, Natl Rick Management Res Lab, Water Supply & Water
Resources Div, Cincinnati, OH 45268 USA
Abstract:
In studies on the formation of disinfection byproducts (DBPs), it is necessary
to scavenge residual active (oxidizing) chlorine in order to rx the
chlorination byproducts (such as haloethanoates) at a point in time. Such research
projects often have distinct needs from requirements for regulatory compliance
monitoring. Thus, methods designed for compliance monitoring are not always
directly applicable, but must be adapted. This research describes an adaptation
of EPA Method 552 in which ascorbic acid treatment is shown to be a
satisfactory means for reducing residual oxidizing chlorine, i.e., HOCl, ClO-,
and Cl-2, prior to determining concentrations of halocarboxylates. Ascorbic
acid rapidly reduces oxidizing chlorine compounds, and it has the advantage of
producing inorganic halides and dehydroascorbic acid as opposed to halogenated
organic molecules as byproducts. In deionized water and a sample of chlorinated
tap water, systematic biases relative to strict adherence to Method 552 were
precise and could be corrected for using similarly treated standards and
analyte-fortified (spiked) samples. This was demonstrated for the quantitation
of chloroethanoate, bromoethanoate, 2,2-dichloropropanoate (dalapon),
trichloroethanoate, bromochloroethanoate, and bromodichloroethanoate when
extracted, as the acids, into tert-butyl methyl ether (MTBE) and esterified
with diazomethane prior to gas chromatography with electron capture detection
(GC-ECD). Recoveries for chloroethanoate, bromoethanoate, dalapon,
dichloroethanoate, trichloroethanoate, bromochloroethanoate,
bromodichloroethanoate, dibromoethanoate, and 2-bromopropanoate at
concentrations near the lower limit of detection were acceptable. Ascorbic acid
reduction appears to be the best option presently available when there is a
need to quench residual oxidants fast in a DBP formation study without
generating other halospecies but must be implemented cautiously to ensure no
untoward interactions in the matrix.
ASCORBIC ACID REDUCTION OF ACTIVE CHLORINE PRIOR TO DETERMINE AMES MUTAGENICITY OF CHLORINATED NATURAL ORGANIC MATTER (NOM)
JOURNAL OF ENVIRONMENTAL MONITORING 2 (3): 253-256 2000
Urbansky ET, Schenck KM
US EPA, Off Res & Dev, Natl Rick Management Res Lab, Water Supply & Water
Resources Div, Cincinnati, OH 45268 USA
Abstract:
Many potable water disinfection byproducts (DBPs) that result from the reaction
of natural organic matter (NOM) with
oxidizing chlorine are known or suspected to be carcinogenic and mutagenic. The
Ames assay is routinely used to assess an overall level of mutagenicity for all
compounds in samples from potable water supplies or laboratory studies of DBP
formation. Reduction of oxidizing disinfectants is required since these compounds
can kill the bacteria or react with
the agar, producing chlorinated byproducts. When mutagens are collected by
passing potable water through adsorbing resins, active chlorine compounds react
with the resin, producing undesirable mutagenic artifacts. The bioanalytical
and chemoanalytical needs of drinking water DBP studies required a suitable
reductant. Many of the candidate compounds failed to meet those needs,
including 2,4-hexadienoic (sorbic) acid, 2,4-pentanedione (acetylacetone),
2-butenoic (crotonic) acid, 2-butenedioic (maleic and fumaric) acids and
buten-2-ol (crotyl alcohol). Candidates were rejected if they (1) reacted too
slowly with active chlorine, (2) formed mutagenic byproducts, or (3) interfered
in the quantitation of known chlorination DBPs. L-Ascorbic acid reacts rapidly
and stoichiometrically with active chlorine and has limited interactions with
halogenated DBPs. In this work, we found no interference from L-ascorbic acid
or its oxidation product (dehydroascorbic acid) in mutagenicity assays of
chlorinated NOM using Salmonella typhimurium TA100, with or without metabolic
activation (S9). This was demonstrated for both aqueous solutions of
chlorinated NOM and concentrates derived from the involatile, ether-extractable
chlorinated byproducts of those solutions.
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