Rh. Jameel et Gr. Helz, Organic chloramines in disinfected wastewaters: Rates of reduction by sulfite and toxicity, ENV TOX CH, 18(9), 1999, pp. 1899-1904
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.