DEGRADATION OF HERBICIDES (AMETRYN AND ISOPROTURON) DURING WATER DISINFECTION BY MEANS OF 2 OXIDANTS (HYPOCHLORITE AND CHLORINE DIOXIDE)

The paper reports the results of an investigation aimed to find out th e number and the chemical structures of byproducts which form during t he reactions occurring in aqueous solution between two very common dis infectants, sodium hypochlorite (NaClO) and chlorine dioxide (ClO2), a nd two herbicides widely used in agriculture and frequently found in g roundwaters: ametryn and isoproturon. Under controlled experimental co nditions [T=20 degrees C, pH=7, reaction-time = 48h, herbicide/disinfe ctant molar ratios: 0.05 and 0.05x10(-2)], ametryn reactions with chlo rine dioxide much slower than with sodium hypochlorite, whereas the op posite trend has been observed for isoproturon. In any case, however, the higher the reagents concentration the faster the reactions. As for reaction byproducts, they have been detected by HPLC and identified b y HPLC-MS. In particular, ametryn (R-S-CH3) reaction with NaClO gives rise to the consecutive formation of four derivatives: the sulphoxide (R-SO-CH3), the sulphone (R-SO2-CH3), the sulphonate ester (R-O-SO2-CH 3) and its hydrolysis product (R-OH). Within the fixed reaction time ( 48h), ametryn reaction with ClO2 forms only the sulphoxide derivative (R-SO-CH3). As for isoproturon, it reacts with both oxidants forming a romatic-ring substituted derivatives. In particular, during the reacti ons with NaClO and ClO2, four and two (chlorinated and/or hydroxylated ) derivatives are respectively formed. (C) 1997 IAWQ. Published by Els evier Science Ltd.