DECHLORINATION KINETICS AT ALKALINE PH OF N-CHLOROPIPERIDINE, A GENOTOXIN IN CHLORINATED MUNICIPAL WASTE-WATER

N-chloropiperidine in chlorinated municipal wastewaters is worthy of a ttention both because of its genotoxicity and because of the acute gen eral toxicity displayed by all chloramines. Here, the rate at which it is reduced and thus detoxified by sulfite is determined in alkaline s olutions. Three parallel reaction paths, with rate constants at 25 deg rees C are: SO32- + ClNC5H10 + H3BO3 (buffer) --> products, k(1) = 565 M-2 s(-1); SO32- + ClNC5H10 + H3O+ --> products, k(2) = 1.13 x 10(11) M-2 S-1 and SO32- + ClNC5H10 + H2O --> products, k(3) = 4.1 M-1 S-1. The activation energy associated with the last (uncatalyzed) pathway i s 30 +/- 2 kJ mol(-1). Exploratory experiments suggest that N-chlorodi ethylamine reacts at a rate similar to N-chloropiperidine whereas N-ch loropyrrolidine reacts about 5 times faster. These are the first syste matic measurements of the rate of dechlorination of secondary N-chlora mines. At the slightly acidic pH of ordinary municipal wastewaters, su ch compounds will be reduced quickly by standard dechlorination practi ces and they cannot contribute significantly to the slowly reduced res idual chlorine that has been discovered in dechlorinated effluents fro m wastewater treatment plants. On the other hand, above pH 8 their lif etime in dechlorinated effluents could become long enough to affect aq uatic wildlife. (C) 1998 Elsevier Science Ltd. All rights reserved.