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Atrazine and Simazine Movement to Wye River Estuary¹

ABSTRACT

The Wye River, a tributary of Chesapeake Bay, is a shallow, well-mixed estuary surrounded by an agricultural watershed, a large portion of which is planted in corn (Zea mays L.). A 3-y study of the movement of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) showed that the total amount of herbicide reaching the estuary depended upon the quantity applied in the watershed and the timing of runoff with respect to application dates. In a year in which significant runoff occurred within 2 weeks of application, 2 to 3% of the atrazine moved to the estuary. In other years with less runoff, or runoff delayed longer after application, much smaller quantities reached the estuary. Simazine loading was one-tenth that of atrazine. Once in the estuary, atrazine and simazine remained in solution, diluted in a conservative manner with estuarine water, and dissipated with a 10- to 30-d half-life. The maximum measured concentration of atrazine was near 15 µg L^–1 but average concentration at peak loading was < 3 µg L^–1. Thus, although the Wye River has a high percentage of watershed land planted to corn, herbicide concentrations rarely approached those producing minor effects on submerged aquatic vegetation.

Key Words: herbicide • agricultural chemicals • triazine herbicides • runoff • estuarine

¹ Contribution of USDA-ARS, Agric. Environ. Qual. Inst., Beltsville, MD 20705, in cooperation with the Dep. of Agron., Univ. of Maryland, College Park, MD 20742.

² Research Chemist and Supervisory Research Chemist, Soil Nitrogen and Environ. Chemistry Lab., USDA-ARS; Plant Physiologist, Pesticide Degradation Lab., USDA-ARS; and Graduate Research Assistant and Assistant Professor of Agron., Univ. of Maryland; respectively.

Received for publication May 2, 1983.