Lindane, photoreactions

The photoreaction of lindane was markedly enhanced in solutions of s commercial soil fulvic acid (Contech) and in natural water samples with higj DOM concentrations (DOC 10-27 mg of C/L) with estimated half-lives a 1-10 days versus a half-life in excess of 100 days in air-saturated distilled watei (Table III). Moreover, Mudambi and Hassett (31) reported that the high chlorinated pollutant, mirex, is reductively dehalogenated to photomirex wit a half-life of 6-8 days under sunlight in Lake Ontario water (eq 15). 

Table III. Photoreaction Kinetics (313 nm) of Lindane in Various Natural Water Samples and Humic Substance Solutions...

In addition to the chloroacetates, as shown by comparisons with the estimates in Table V, the half-lives for both lindane and mirex in the natural water samples would have been considerably longer than those observed, had reaction with solvated electrons in bulk solution been the dominant mechanism for photoreaction. The higher efficiency of these halocarbon reactions may be attributable to sorption of the chloroacetates on the NOM, which permits more facile electron capture. Other possible pathways for reactions of sorbed halocarbons include direct photoreduction by excited states of the NOM, which, like solvated electrons, also are quenched by oxygen. Alternatively, the enhancement may involve other direct electron-transfer mechanisms such as amine-halomethane reactions. These alternative possibilities are examined in the following section. 

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