TOXICOLOGY OF DRINKING-WATER DISINFECTION BY-PRODUCTS FROM NUTRIENTS - RATE STUDIES OF DESTRUCTION OF POLYUNSATURATED FATTY-ACIDS INVITRO BY CHLORINE-BASED DISINFECTANTS

As model reactions between unsaturated fats and water disinfectants in the GI tract, relative rates of destruction of seven polyunsaturated fatty acids (L, alpha-Ln, gamma-Ln, Ara, EPA, DH, and DT) by OCl- and NH2Cl were investigated in vitro. Using millimolar solutions of seven PUFAs combined with various OCl- mole ratios, disappearance of PUFAs was followed by UV spectrophotometry at pH = 9.5 and at 35-degrees-C via conjugated hydroperoxydienes at 234 nm. While OCl- rapidly destroyed all PUFAs, NH2Cl was inert. Overall second-order rate constants computed for L at increasing times disclosed that the attack on the cis-CH=CHCH2CH=CH moiety by OCl- does not follow simple second-order kinetics. Using a logit-log transform and second-order polynomial regression analysis of L's disappearance in a stoichiometric ([L] = 1.2 mM; [ClO-] = 2.4 mM) mix, data were analyzed by the time ratio method of Schwemer and Frost. These agreed with a sequential system of at least two irreversible second-order reactions having k1 = 15.6 L.mol-1.s-1 and k2 = 2.6 L.mol-1.s-1. Preliminary GC/MS analysis indicated that the initial product is a mix of chlorohydrin isomers. These undergo second addition of HOCl and/or lose halogens and polymerize. Additional minor products were also C5-C9 mono- and bifunctional carboxylates and mixed acid aldehydes. Studies with mol equiv of Cl- - free (ClO-)-Cl-36 allowed estimation of covalent binding of Cl by L at various times, supporting the kinetic findings. For other PUFAs of higher degree unsaturation, the complexity of feasible reactions precluded an analogous approach. As a substitute, reactions of each PUFA at identical molarities and conditions were followed. Using logit-log transforms again, relative apparent rates were computed at tl/2, showing that increasing unsaturation and chain length decreases reactivity with OCl-. Binding of Cl-36 showed that PUFAs of increasing unsaturation are principally destroyed via oxidation.