The vertical fluxes of alachlor, atrazine, simazine, and toxaphene were measured by air-sampling and aerodynamic measurements over a 24-day period after surface application to a fallow soil in eastern Maryland. The triazines were applied at 1.68 kg/ha as a wettable powder formulation and alachlor and toxaphene at 2.24 and 2.52 kg/ha, respectively, as emulsifiable concentrates. Calculated volatilization losses in the first 21 days were 780 g/ha toxaphene, 420 g/ha alachlor, 40 g/ha atrazine, and 21 g/ha simazine. Daily losses varied with soil moisture content, alachlor and toxaphene volatilization being reduced as the surface soil layers became dry. Daily volatilization patterns of atrazine and simazine indicated that some wind erosion of wettable powder formulation occurred as the surface soil dried, but the amounts transported were small. Volatilization losses of triazines were much smaller than disappearance by chemical degradation. A simple empirical equation was shown to yield estimated volatilization rates that were within about a factor of 10 of field-measured rates for six of eight compounds whose vapor pressures spanned a range of 104.

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.