A spectrofluorimetric study of the binding of carbofuran, carbaryl, and aldicarb with dissolved organic matter

Abstract

This study examined the binding of carbamate pesticides with dissolved organic matter (DOM) using fluorescence quenching and synchronous scan fluorescence spectroscopy (SSFS). Fluorescence spectra of the three pesticides were characterized as follows: carbofuran and carbaryl fluoresce at 305 and 330 nm, respectively, upon excitation at 276–279 nm, whereas, aldicarb shows broad emission at 350–380 nm upon excitation at 326 nm. A fluorescence quenching technique was used to obtain conditional binding constants for the carbamate pesticides with Aldrich humic acid under fixed conditions of 22°C and pH 6. The binding constant of carbofuran with humic acid is greater than the binding constants of both carbaryl and aldicarb. Estimates were also obtained for the binding of carbofuran with DOM samples from a coniferous forest soil O horizon, a deciduous forest soil O horizon, a sedge marsh wetland, and a stream in the drainage sequence and their molecular weight (MW) fractions. Those conditional binding constants were used to predict the potential transport of carbofuran in the drainage sequence. When binding constants and DOM concentrations were both taken into account, it was found that DOM from the coniferous forest O horizon had the largest capacity to bind and to transport carbofuran in the drainage sequence. SSFS was used to probe the binding mechanisms of DOM with carbofuran. Overall, the potential mobility of carbofuran in the upland–wetland–stream drainage sequence was significantly enhanced via binding with DOM.