Herbicides and Herbicide Degradation Products in Upper Midwest Agricultural Streams during August Base‐Flow Conditions

Abstract

Herbicide concentrations in streams of the U.S. Midwest have been shown to decrease through the growing season due to a variety of chemical and physical factors. The occurrence of herbicide degradation products at the end of the growing season is not well known. This study was conducted to document the occurrence of commonly used herbicides and their degradation products in Illinois, Iowa, and Minnesota streams during base-flow conditions in August 1997. Atrazine, the most frequently detected herbicide (94%), was present at relatively low concentrations (median 0.17 microg L(-1)). Metolachlor was detected in 59% and cyanazine in 37% of the samples. Seven of nine compounds detected in more than 50% of the samples were degradation products. The total concentration of the degradation products (median of 4.4 microg L(-1)) was significantly greater than the total concentration of parent compounds (median of 0.26 microg L(-1)). Atrazine compounds were present less frequently and in significantly smaller concentrations in streams draining watersheds with soils developed on less permeable tills than in watersheds with soils developed on more permeable loess. The detection and concentration of triazine compounds was negatively correlated with antecedent rainfall (April-July). In contrast, acetanalide compounds were positively correlated with antecedant rainfall in late spring and early summer that may transport the acetanalide degradates into ground water and subsequently into nearby streams. The distribution of atrazine degradation products suggests regional differences in atrazine degradation processes.

The quality of our Nation's waters: water quality in the glacial aquifer system, northern United States, 1993-2009

“…(72,73) Groundwater can be an important source of pesticides to streams, particularly during dry periods when the proportion of streamflow composed of groundwater discharge is at its maximum; this can lead to the exposure of aquatic organisms to potentially harmful levels of pesticides. (24,74) Although pesticides are detected frequently in the glacial aquifer system, they are nearly always measured at concentrations well below human-health benchmarks. The pesticides atrazine (and its degradate deethylatrazine), metolachlor, simazine, prometon, and bentazon were among the pesticides detected most frequently in groundwater, but fewer than 5 percent of samples contained one of these compounds at a concentration above the common assessment level of 0.2 µg/L -a level that is many times lower than any human-health benchmark.…”

“…The amount and timing of the pesticide applications and of long-term changes in rainfall and runoff patterns can enhance or reduce this effect. (74,83) The types and concentrations of pesticides in groundwater under the influence of surface water will change in response to introduction of new pesticides, changing land-use practices, and climate changes. degradation The breakdown of a compound to a chemically simpler compound by abiotic or biotic processes.…”

Evaluation of the risk of mixtures of paddy insecticides and their transformation products to aquatic organisms in the Sakura River, Japan

“…Public concern about the adverse effects of pesticides and their TPs on water quality and aquatic organisms is increasing. Monitoring surveys of pesticides [1][2][3] have detected some of their TPs at much higher concentrations than their parent compounds [4].…”

Peer Reviewed: When Synthetic Chemicals Degrade in the Environment

“…Specifically, research on pesticides has found degradates in surface water (5)(6)(7)(8)(9)(10), groundwater (11)(12)(13), precipitation (14)(15)(16), air (17,18), and sediment (19,20).…”