FORMATION OF HERBICIDE DEGRADATION BY-PRODUCTS DURING GROUNDWATER DISINFECTION - AN LC-MS INVESTIGATION

The number and the chemical structure of by-products forming in the re actions occurring after the addition of two common disinfectants, sodi um hypochlorite and chlorine dioxide, to aqueous solutions containing two herbicides widely used in agriculture and frequently found in grou ndwaters, i.e., Terbutryn and Isoproturon were found. All the reaction s were carried out under the following controlled experimental conditi ons: T= 25 degrees C; pH 7; t(c) (contact time) = 48 h; and herbicide- disinfectant concentration ratio, (0.05 x 10(-3) M)/(I x 10-3 M). Unde r such experimental conditions, Terbutryn reacted with chlorine dioxid e much slower than with sodium hypochlorite, while the reverse trend w as found out for Isoproturon. Reaction by-products were detected by HP LC and identified by HPLC-MS; however, for Isoproturon, the identifica tion is still under way. Isoproturon reacts forming six different by-p roducts: four with NaClO and two with ClO2. Experimental evidence supp orts the hypothesis that Isoproturon reacts with the selected disinfec tants in two different ways. This herbicide, in fact, presumably under goes oxidation by ClO2 and substitution by NaClO. Terbutryn (T-S-CH3), instead, is oxidized by both disinfectants. In particular this herbic ide forms four identified derivatives with NaClO: the sulphoxide (T-SO -CH3), the sulphone (T-SO2-CH3), the sulphonate ester (T-O-SO2-CH3), a nd the hydrolysis product (T-OH), while it forms only the sulphoxide d erivative (T-SO-CH3) with ClO2.