Date of Award

8-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Laurie Osher

Second Committee Member

Andrew S. Reeve

Third Committee Member

David E. Yarborough

Abstract

For the past twenty years hexazinone has been the most widely used broadspectrum herbicide available to eliminate competition by weeds in blueberry fields. Hexazinone is highly toxic to periphyton communities (EC50 3 μg/L) and phytoplankton (EC50 10 μg/L); is highly soluble in water (33,000 mg/L at 25° C); has low organic carbon partition (Koc 40 m3/kg); and a long half-life in the groundwater persisting for over eight years in the groundwater of sand and gravel soils. As a result, it moves to groundwater when applied to fields in the region's glacial outwash soils and flushes out to surface waters where it has a potential to impact aquatic flora. Hexazinone has been detected in the groundwater and surface waters in Hancock and Washington Counties for more than a decade. In both counties, hexazinone was found in the groundwater from the blueberry fields to the streams, rivers, and estuaries of Down East, Maine. Despite a four-fold decrease in the application rate of hexazinone since 1983, concentrations in groundwater have changed very little. This research measured concentrations of hexazinone in two Down East, Maine watersheds. The first was a long term study of hexazinone concentrations in the groundwater and surface waters of Washington County. These concentrations were compared to precipitation data to determine if there was a correlation. Concentrations of hexazinone ranged from below detection to 145 μg L-1. At one study site in Washington County, a hexazinone treatment of 1.5 kg/ha was applied in 1993. After ten years without subsequent treatment, the herbicide was still measurable in the groundwater beneath the field. In a second study in Hancock County, a 1994 town well capable of pumping 64,000 gallons a day was installed in the center of the aquifer between several blueberry barrens and the estuary. When in operation, a pump alters the rate and direction of the groundwater flow. Concentrations of hexazinone were still measurable in all the sample locations along the sand and gravel deposit between the barrens and the estuary, but the large drawdown area may have affected the magnitude of concentrations at the time of measurement.

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