| Description |
Approximately 242 million kg of herbicides is applied in the United States of America (USA) annually. Chloroacetamides are one of the commonly used herbicide classes in the USA. While herbicides prevent the growth of weeds, they can damage crops, resulting in so-called "herbicide injury." Recognition of herbicide injury resulted in research and development of synthetic compounds called "herbicide safeners." Dichloroacetamides are a commonly used class of safeners. The use of these compounds as an inert ingredient is increasing as the co-formulant in herbicides, yet little is known about the distribution and fate and transport of safeners. Two dichloroacetamide safeners, benoxacor and furilazole, were chosen for this study. Identification of safeners in surface water samples is a first indication of the potential persistence of these compounds. Therefore, a total of 237 surface water samples from 37 US states were measured at the University of Utah for the presence of safeners. Benoxacor and furilazole were detected in water samples from 29 and 30 US states, respectively. The aqueous solubility of benoxacor and furilazole was 22 and 235 mg/L, respectively. The log octanol-water partition coefficient of benoxacor and furilazole was 2.23 and 1.96, respectively. Both benoxacor and furilazole oxidation were found to be second order with respect to initial KMnO4 concentrations. A batch equilibrium experiment was followed to study the adsorption-desorption of the safeners onto Granulated Activate Carbon (GAC) and three different soils. The results of these studies show that the safeners under study, benoxacor and furilazole, are present in the surface water as shown by their detection in surface water samples. Photo-oxidation is unlikely for the safeners from agricultural fields and surface water. The benoxacor may adsorb to soil in agricultural fields and probably river sediment. Furilazole does not have high adsorption capacity on soil so it might leach from the field of application. Further, these studies suggest drinking water treatment plants using GAC might remove these safeners through sorption of these compounds. Also, pre-dosing potassium permanganate may oxidize these compounds at levels commonly used in treatment plants. Ultraviolet oxidation for disinfection may further degrade the compounds. Biodegradation of benoxacor and furilazole is likely to happen in the environment. |
