Herbicide Runoff From Experimental Watersheds

Abstract

Two commonly used herbicides in corn fields of the Rhode River Watershed were atrazine (2‐chloro‐4‐ethylamino‐6‐iso‐propylamino‐1,3,5‐triazine) and alachlor (2‐chloro‐2′,6′‐diethyl‐N‐methoxymethyl acetanilide). Although alachlor was applied in larger quantities, atrazine was detected more frequently in runoff waters and had greater concentrations than alachlor (0–40 µg/L vs. 0–6 µg/L). Atrazine was more persistent and more mobile in watershed soils. Linear regression analysis of herbicide loading rates and percentage agricultural land‐use did not give a direct relationship. Runoff waters from forest watersheds where herbicides were not directly applied, were contaminated with herbicides. During the 3‐y study period (1976–1978), a maximum of 10 µg/L of atrazine, and up to 0.5 µg/L alachlor were discharged in winter runoff waters from the eight experimental watersheds. In addition to quantity of herbicides directly applied to land surface, residual levels in runoff waters must be influenced by other important factors such as topography, location of croplands in relationship to drainage channel, etc. A major portion of atrazine was found in dissolved aqueous form in runoff‐water samples collected during storm events. Percolation in subsurface flow and dissolution in overland flow were believed to be important transport mechanisms.

Pesticides report 34. Pesticide runoff: Methods and interpretation of field studies (Technical Report)

“…For all but the most hydrophobic pesticides, the majority of transport is in the water phase (ref. 4,19,20,23,41).…”

The role of storm flows in concentration of pesticides associated with particulate and dissolved fractions as a threat to aquatic ecosystems - Case study: the agricultural watershed of Save river (Southwest of France)

“…For instance, the "Directive" concerning the quality of water intended for human consumption of the European Union foresees standards for pesticide residue in drinking water at 0.1 µg·L −1 for each active substance and 0.5 µg·L −1 for the sum of all pesticides (EEC, 1991). Higher rates of water contamination during storm events have been demonstrated by several investigators (Wu et al, 1983;Roth et al, 1992;Bach et al, 2001;Taghavi et al, 2010). However, little is known about the mechanisms of pesticide transfers from soils to stream waters, and about the parameters which control these transfers.…”

Response of aquatic communities from a vermont stream to environmentally realistic atrazine exposure in laboratory microcosms

“…In 1989, an estimated 29 million kilograms of atrazine active ingredient were applied to crops in the United States [1], and atrazine has been detected in both surface water [2][3][4][5] and groundwater [6]. Studies of the occurrence and behavior of atrazine in streams and rivers draining agricultural lands have shown that the highest atrazine concentrations usually occur in relatively brief pulses following rain events, especially those that occur soonest after herbicide application [3,[7][8][9][10]. Dilution and degradation usually reduce atrazine concentrations in streams within a few weeks of the rain event [5,7,11].…”