A SPECTROFLUOROMETRIC STUDY OF THE BINDING OF CARBOFURAN, CARBARYL, AND ALDICARB WITH DISSOLVED ORGANIC-MATTER

This study examined the binding of carbamate pesticides with dissolved organic matter (DOM) using fluorescence quenching and synchronous sca n fluorescence spectroscopy (SSFS). Fluorescence spectra of the three pesticides were characterized as follows: carbofuran and carbaryl fluo resce at 305 and 330 nm, respectively, upon excitation at 276-279 nn, whereas, aldicarb shows broad emission at 350-380 nm upon excitation a t 326 nm. A fluorescence quenching technique was used to obtain condit ional binding constants for the carbamate pesticides with Aldrich humi c acid under fixed conditions of 22 degrees C and pH 6. The binding co nstant of carbofuran with humic acid is greater than the binding const ants of both carbaryl and aldicarb. Estimates were also obtained for t he binding of carbofuran with DOM samples from a coniferous forest soi l 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 t he potential transport of carbofuran in the drainage sequence. When bi nding constants and DOM concentrations were both taken into account, i t was found that DOM from the coniferous forest O horizon had the larg est capacity to bind and to transport carbofuran in the drainage seque nce. SSFS was used to probe the binding mechanisms of DOM with carbofu ran. Overall, the potential mobility of carbofuran in the upland-wetla nd-stream drainage sequence was significantly enhanced via binding wit h DOM. (C) 1998 Published by Elsevier Science B.V. All rights reserved .