2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridine carboxylate; imazapyr (ISO)

Toxicity to terrestrial plants

Description of key information

The most sensitive species in a terrestrial phytotoxicity study was lettuce. The NOEC for dry weight was 408 g/ha. The calculated EC25 and EC50 values were 681 (95 % confidence interval; 378 to 983) and > 1670 g/ha, respectively.

Assuming a mixing depth of 0.12 m (depth of the pots used in the study) and a soil density of 1700 kg/m³ an application rate of 408 g/ha would result in a concentration of 0.0002 g/kg.

Additional information

Key study (BASF SE, 84495, 2002)

In a non-target terrestrial phytotoxicity study the effect of the test substance on seedling emergence and growth of selected non-target terrestrial plants was assessed according to EPA OPPTS 850.4100 and EPA OPPTS 850.4225 (Tier I and Tier II). The effect of the test material on seeding emergence and growth of monocot (corn - Zea mays, oat - Avena sativa, onion - Allium cepa, ryegrass - Lolium perenne) and dicot (cabbage - Brassica o/eracea, carrot - Daucus carota, cucumber - Cucumis sativus, lettuce - Lactuca sativa, soybean - Glycine max, tomato - Lycopersicon esculentum) crops was studied at nominal treatments rates of 1690 and 1720 grams per hectare (g/ha) for tier I testing. The nominal application rates for the lettuce and ryegrass tier II testing were 0.0 (control), 0.0 (vehicle control), 104, 208, 417, 834, and 1670 g per hectare. The nominal application rates for the carrot tier II testing were 0.0 (control), 0.0 (vehicle control), 107, 213, 427, 854, and 1710 g per hectare. The negative control and vehicle control plants were sprayed with an equivalent amount of deionized water or a 50 % methanol and water mixture.

Cabbage, carrot, corn, cucumber, oat, onion, soybean, and tomato did not display detrimental effects ≥ 25% for any of the test parameters (i.e., % emergence, mean shoot length, or mean dry weight) when exposed to calculated application rates of 1650 to 1690 gram per hectare. In the tier I testing, ryegrass seedlings treated with 1690 g/ha displayed a -44 % difference in dry weight versus the vehicle control value, however, during the tier II testing ryegrass did not display detrimental effects ≥ 25 % for any of test parameters. The most sensitive species was lettuce. In the tier I lettuce test, there was a 30 % decrease in treatment dry weight as compared to the vehicle control. Dry weight was also the most sensitive parameter during the tier II lettuce testing. The NOEC for this parameter was 408 g/ha. The calculated EC25 and EC50 values were 681 (95 % confidence interval; 378 to 983) and > 1670 g/ha, respectively.

 

Supporting study (American Cyanamid Company, 0450, IZ-549-001, 1988)

In a seedling emergence and vegetative vigor test comparable to OPPTS 850.4100, the effect of the test item was tested upon following plants: corn, wheat, sugarbeets, sunflower, tomato, cucumber, oats, onions, soybeans and green peas. The test item has a detrimental effect on all species tested. Seedling emergence was least affected of all parameters. The test item usually inhibited the growth in a rate responsive manner, as herbicide rates increased crop injury also increased. The test item was more injurious to oats and wheat than to any of the other crops tested.

Supporting study (American Cyanamid Company, 0450b, IZ-549-002, 1988)

In a vegetative vigor study comparable to OPPTS 850.4150, the effect of the test item was test upon following plants: corn, wheat, sugarbeets, sunflower, tomato, cucumber, oats, onions, soybeans and green peas. The test item is a broad spectrum non-selective herbicide that has the potential to kill seedlings of many species when applied post-emergence to the foliage. Green peas were by far the most tolerant crop species to post-emergence applications of the test item. All other crop species tested showed higher sensitivity to the test item. Sugarbeets were by far the most sensitive crop species (affected at rates of 0.548 g/ha). Larger seedlings were able to tolerate higher levels of the test item than smaller seedlings. In general, the monocot species could withstand up to 8.75 g/ha of the test item without noticeable crop injury. Dicot species were more variable in the amount of the material they could tolerate.  Larger seeded species were able to tolerate higher levels of the test item.

The exposure of the plants was via foliar application and due to the fact that this exposure pathway is not relevant under REACH, this study was not considered for the further assessment.