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Outdoor pools (2.3 x 2.3 m) were used to simulate typical rice agricultural practices in Louisiana, USA, to evaluate the toxicity of ICON (active ingredient [a.i.] fipronil) and its degradates to crayfish (Procambarus clarkii). Six paddies were planted with seed treated with ICON 6.2 FS at an exaggerated application rate of 0.05 kg a.i./ha (recommended rate, 0.042 kg a.i./ha), simulating three rice-planting scenarios. Two reference paddies were planted with untreated seed. Crayfish were exposed to tail water within 24 to 48 h after seeding, simulating standard Louisiana agricultural and water management practices. At 50 d after planting, a separate group of crayfish was caged in situ for 14 d to evaluate toxicity. An additional 50 crayfish were added to two paddies approximately 100 d after rice planting and held for 29 weeks to evaluate bioaccumulation. Residues of fipronil and its degradates in water and soil were similar to residue concentrations measured from rice fields in Louisiana. Tail water from the treated paddies was not toxic to crayfish. The fipronil 96-h median lethal concentration (LC50) for adult crayfish was 180 microg/L, which would provide at least a sixfold safety factor between the maximum fipronil concentration in tail water and the crayfish LC50. In situ exposures of crayfish also were not toxic. Concentrations of fipronil and its degradates after 29 weeks of exposure were less than 5 microg/kg in crayfish tail muscle tissue. These results demonstrate that label instructions adequately protect crayfish in a rice-crayfish cropping scenario when ICON is applied at maximum application rates as a seed treatment.

No abstract

Ten species of terrestrial plants, including 6 dicotyledonous and 4 monocotyledonous species, were exposed to a direct overspray of atrazine according to US Environmental Protection Agency seedling emergence and vegetative vigor study guidelines and subsequently evaluated for potential recovery. For each species, no-observed-effect rate (NOER), 10% effect rate, 25% effect rate, and 50% effect rate 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 the rates subsequently were compared. For the seedling emergence study, the standard experimental (designated test 1) and recovery (designated test 2) phases encompassed days 0 to 14 and days 14 to 28, respectively. Similarly, for the vegetative vigor study, test 1 and test 2 encompassed days 0 to 21 and days 21 to 42, respectively. Plants were exposed to atrazine at nominal application rates ranging from 1.1 g active ingredient (a.i.)/ha (0.0010 lb a.i./A) to 28,000 g a.i./ha (25 lb a.i./A), depending on the species; the 28,000 g a.i./ha rate is greater than 12 times the maximum application rate of 2250 g a.i./ha (2 lb a.i./A) registered on corn. For seedling emergence, only 2 of 10 species tested, cabbage and tomato, provided clear rate responses in the initial 14 d of exposure (test 1). Based on a comparison of x% effect rate (ERx) and NOER values for growth rates of shoot length and shoot dry weight for days 0 to 14 relative to days 14 to 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 8 species showed either a weak response that did not allow a clear assessment of recovery or no response at all. For the vegetative vigor study, 9 of the 10 species tested provided clear rate responses in test 1 (days 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 to 21 (test 1) relative to day 21 to 42 (test 2) ERx and NOER values for shoot length, average growth rates indicated that 8 of 9 species clearly demonstrated an increase in 2 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 7 of the 9 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.

No abstract