John Wiley & Sons, Ltd.

Recovery of Terrestrial Plants in Vegetative Vigor and Seedling Emergence Tests from Exposure to Atrazine

Ten species of terrestrial plants, including six dicotyledonous and four monocotyledonous species, were exposed to a direct overspray of atrazine according to U.S. EPA seedling emergence and vegetative vigor study guidelines and subsequently evaluated for potential recovery. For each species, NOER, ER10, ER25, and ER50 values were calculated (where possible) for a variety of guideline required endpoints (but focusing on growth rate) for both the standard experimental phase and a recovery phase and subsequently compared. For the seedling emergence study, the standard experimental (designated Test 1) and recovery (designated Test 2) phases encompassed day 0‐14 and day 14‐28, respectively. Similarly, for the vegetative vigor study, Test 1 and Test 2 encompassed day 0‐21 and day 21‐42, respectively. Plants were exposed to atrazine at nominal application rates ranging from 1.1 (0.0010 lb a.i./A) to 28,000 g a.i./ha (25 lb a.i./A), depending on the species, where the 28,000 g a.i./ha rate is greater than twelve times the maximum application rate of 2250 g a.i./ha (2 lb a.i./A) registered on corn. For seedling emergence, only two of ten species tested, cabbage and tomato provided clear rate‐responses in the initial 14 days of exposure (Test 1). Based on a comparison of ERX and NOER values for growth rates of shoot length and shoot dry weight for day 0‐14 relative to day 14‐28, recovery was apparent for cabbage shoot length growth rate and tomato shoot length and shoot dry weight growth rates. Test application rates selected for the remaining eight species either showed a weak response that did not allow a clear assessment of recovery or no response at all. For the vegetative vigor study, nine of the ten species tested, provided clear rate‐responses in Test 1 (day 0‐21); corn did not demonstrate any herbicidal response up to the highest rate tested, 28,000 g a.i./ha. Based on comparison of day 0‐21 (Test 1) relative to day 21‐42 (Test 2), ERX and NOER values for shoot length, average growth rates indicated that eight of nine species clearly demonstrated an increase in two or more metrics (cabbage did not demonstrate a response based on shoot length). Clear recovery was also indicated by an increase in ERX and/or NOER values from Test 1 to Test 2 for shoot dry weight average growth rates for seven of the nine species (corn did not show a response and oat and soybean showed variable responses). Thus, in most species, where initial herbicidal effects were observed, the effects are largely ameliorated over time. This article is protected by copyright. All rights reserved

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