Atrazine and Simazine Movement to Wye River Estuary

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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.