Organic chloramines in disinfected wastewaters: Rates of reduction by sulfite and toxicity

Peptides and protein fragments that have been monochlorinated at terminal a mino-N sites are known to react sluggishly with S(IV) dechlorinating agents in wastewater treatment plants. Persistence of these chloramines may imper il downstream aquatic organisms. Reactivity of sidechain amino-N is explore d in this paper, and previous kinetic information on chloramine reduction b y S(IV) is summarized. Much like other chloramines, side-chain chlorinated N-chloroacetyllysine reacts with SO32- in berate buffer at 25 degrees C acc ording to the law rate = [SO32-][chloramine] (520[H3BO3] + 5.7 x 10(10)[H3O +] + 4.1) (time in s, concentration in M). Apparently because of their grea ter basicity, aliphatic monochloramines such as N-chloroacetyllysine are re duced rapidly at near-neutral pH, in contrast to terminally chlorinated pep tides. At pH >10, all monochloramines will be reduced at nearly the same, q uite slow rate (t(1/2) approximate to 0.1/[SO32-]; time in s, SO32- in M). Microtox(TM) (Azur Environmental, Carlsbad, CA, USA) bioassays indicate tha t two terminally chlorinated N-chloropeptides as well as side-chain chlorin ated N-chloroacetyllysine are much less toxic to Vibrio fisheri than NH2Cl N-chloroglycine, and N-chloropiperidine. An astonishingly simple relationsh ip describes the bioassay results at 5 min exposure as In(EC50) = -3.684 0.0221(MW) (EC50 in mg/L as Cl-2; molecular weight [MW] in Daltons). These exploratory data offer a basis for optimism that S(IV)-surviving N-chlorope ptides will prove less toxic in natural ecosystems than rapidly reduced chl oramines, but further investigations are needed.