Experimental techniques for the investigation of aerobic biodegradation of hexazinone

Abstract

Hexazinone, sold under the trade names Velpar and Pronone, is a triazine herbicide widely used in the commercial production of wild blueberries. The University of New Brunswick Groundwater Studies Group, the New Brunswick Department of Agriculture, the New Brunswick Department of the Environment and Agriculture and Agri-Food Canada initiated a hexazinone-groundwater quality project in Southwestern New Brunswick in 1995 to provide scientific information to the wild blueberry industry. The objectives of this project were to 1) to evaluate the extraction methods for removing hexazinone from residually-saturated sandy material, and 2) to assess hexazinone degradation and chemical oxygen demand (COD) removal in several aerobic bacterial reactors. Two different sample extraction methods were evaluated for the efficiency of hexazinone mass recovery from residually-saturated sand. The second extraction method proved to be the better approach for recovering hexazinone mass, recovering 95% to 100% of hexazinone mass, while the first method recovered 89% to 98% of the hexazinone mass. No appreciable degradation was found in any of the aerobic bacterial reactors. Hexazinone may have been toxic to the bacteria at the high concentration of 750 mg/L; at lower concentrations of approximately 100 mg/L, a viable bacterial population was established however diauxie was occurring. All aerobic bacterial reactors, excluding 4B and 5B, were nutrient limited in the early stages. Therefore, it took an extended period of time to establish a bacterial population capable of removing COD, thus increasing the required acclimation period.