Atrazine and Simazine Movement to Wye River Estuary

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.

Transport of herbicides and nutrients in surface runoff from corn cropland in southern Ontario

“…5) were greatest in set I (about 1.0 mg L-'). Glotfelty et al (1984) found that rhe concentration of atrazine in runoff peaked at 0.3 mg L -r in the first significant runoff volume after application. …”

“…a). Glotfelty et al (1984) found thar in years in which significant runoff occurred within 2 wk of herbicide application, 2-3% of the atrazine was transported via streams to the estuary.…”

Soil erosion, runoff and nutrient losses in an avocado (Persea americana Mill) hillside orchard under different groundcover management systems

“…Off-site movement of nutrients and pesticide residues in runoff is a well-documented source for pollution of surface and groundwater (Sims et al 1998;Glotfelty et al 1984;Leonard 1990;Braun and Hawkins 1991;Simmons and Leyva 1994). Nonetheless, there are few reports on the effects that groundcover management systems have on the load of nutrient and herbicide residues exiting high input perennial cropping systems established on steep hillsides.…”

Estuarine phytoplankton group-specific responses to sublethal concentrations of the agricultural herbicide, atrazine

“…Widespread use of atrazine promotes this herbicide as a common contaminant in streams, rivers, and lakes (Solomon et al, 1996;Clark et al, 1999). In microcosm studies, the reported environmental half-lives of atrazine range from 30 to 120 days in aqueous solutions exposed to natural conditions (Cunningham et al, 1984;Glotfelty et al, 1984;Kemp et al, 1985). Biodegradation is negligible due to the s-triazine ring, which is resistant to microbial attack (Howard, 1991).…”

“…Biodegradation is negligible due to the s-triazine ring, which is resistant to microbial attack (Howard, 1991). Estuaries can accumulate atrazine from both acute and chronic loading events (Jones et al, 1982;Glotfelty et al, 1984;Isensee, 1987;Kemp et al, 1985). The long water residence time in estuaries coupled with high atrazine loading rates may result in prolonged exposure of phytoplankton communities to atrazine.…”