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

Endpoint summary

Description of key information

Hydrolysis:

The test substance is stable to hydrolysis at environmental relevant pH values and temperatures.

Phototransformation in water:

Half-life (t1/2) values for carbon-14 labeled test substance in distilled water and pH 5 and pH 9 solutions under simulated sunlight:

Aqueous Media	Half-life (t1/2) (days)
	Based on 24 h light/day	Based on 12 h light/day
A.     Carboxl Carbon-14 Label
Distilled Water	1.9	3.7
pH 5 Buffer	2.7	5.3
pH 9 Buffer	1.3	2.5
B.     Carbonyl Carbon-14 Label
Distilled Water	2.3	4.5

Phototransformation in soil:

The test substance degraded slowly on irradiated sandy loam soil, with an extrapolated half-life of 149 days.

Additional information

Hydrolysis:

Key study (American Cyanamid Company, PD-M 19-8, 1982)

A hydrolysis study was conducted to determine the rate of hydrolysis and degradation products of the test substance at a concentration of 50 ppm in pH 5.0, 7.0 and 9.0 buffer solutions and in distilled water at 25 °C. The test substance was stable in aqueous buffer solutions (pH 5 and 7) and distilled water (pH 5.2) for up to 30 days at 25 °C. Only 1.0% of the test substance had degraded in each of the pH 5.0 and pH 7.0 buffer solutions, and 1.4% in the distilled water solution. The test item degraded slowly in an aqueous pH 9 buffer solution. At this pH 7.3% of the test item had degraded at the end of 30 days and the half-life at pH 9.0 was calculated to be 325 days. The only identified degradation product was Nicotinic acid, 2-[(1-carbamoyl-1,2-dimethylpropyl)-carbamoyl]-. Minor degradates were not identified.

Phototransformation in water:

Key study (American Cyanamid Company, PD-M Volume 20-20, 1983)

The photodegradation in water of the test substance was investigated in a laboratory study equivalent to OPPTS 835.2240. The photolysis of the carboxyl carbon-14 and carbonyl carbon-14 labeled test substance was studied in distilled water, potassium acid phthalate buffer (pH 5.0), and boric acid buffer (pH 9.0). The test substance was dissolved in each media at a concentration of 25 ppm and exposed continuously at 25 °C in an environmental chamber to simulated sunlight (borosilicate-filtered Xenon arc lamp) for a period of 10 days.

The test substance photodegrades rapidly in various aqueous media under simulated sunlight and follows first order kinetics. The half-life of the carboxyl carbon-14 labeled test substance in distilled water, pH 5 and pH 9 buffer solutions under the tested conditions were calculated as 1.9 days (3.7 days on 12 hour exposure), 2.7 days (5.3 days on 12 hour exposure), and 1.3 days (2.5 days on 12 hour exposure), respectively. The half-life of the carbonyl carbon-14 labeled test substance in distilled water was calculated as 2.3 days (4.5 days on 12 hour exposure). The photodegradation rate of the test substance was slightly higher at higher pH.

The amount of nonvolatile carbon-14 radioactivity from carboxyl carbon-14 and carbonyl carbon-14 labeled test substance remaining in distilled water at the end of 10-day continual exposure were 92.5% and 23.4% of the total applied radioactivity, respectively. The nature of the lost carbon-14 radioactivity from distilled water was determined to be carbon-14 carbon dioxide in separate trapping experiments.

The carboxyl carbon-14 labeled test substance found in distilled water at the end of 10-day continual exposure was 2.7% of the total carbon-14 radioactivity. Carboxyl carbon-14 labeled test substance in distilled water photodegraded into Furo[3,4 -b]pyridin-5(7H)-one-7-hydroxy-, 2 (29.7%), 2,3 -Pyridinedicarboxylic acid (22.7%), Quinolinimide (trace) and Furo[3,4 -b]pyridine-5(7H)-one (trace). There were about 25 other unknowns comprising 37.7% with none exceeding 10 % of the total carbon-14 radioactivity.

The carbonyl carbon-14 labeled test substance found in distilled water at the end of 10-day continual exposure was 4.4% of total carbon-14 radioactivity. The only major degradation product derived from carbonyl carbon-14 labeled test substance in distilled water was carbon dioxide. There were about 24 other unknowns comprising 19.0% with none exceeding 10% of the total carbon-14 radioactivity. The test substance was stable in the dark during 10-day incubation period.

In another study the residues of the test substance and the two degradation products, 7-hydroxyfuro[3,4-b]pyridine-5(7H)-one and 2,3-pyridinecarboxylic acid, in aquatic field dissipation for Arsenal 2AS herbicide applied to freshwater ponds in Florida, were determined during summer months (American Cyanamid Company, RES 99-059, 1999). Arsenal 2AS herbicide was applied to the ponds at a rate of 1.6 Ib ae/A.
The residues of the test substance, in pond water from treated pond 11 averaged 25 ppb at 1 hour after treatment and declined to <1.00 ppb at the 42 days after treatment (DAT). The residues of the test substance, in pond water from treated pond 21 averaged 92.9 ppb at 1 hour after treatment and declined to <1.00 ppb at the 42 DAT. The test substance in pond water for pond 21, resulted in a half-life of 3.9 days in this study. The residues of the test substance, in pond sediment from treated pond 11 averaged 4.3 ppb at 1 DAT and declined to <1.00 ppb at the 14 DAT. The residues of the test substance, in pond sediment from treated pond 21 averaged 11.3 ppb at 6 hour after treatment and declined to <1.00 ppb at the 90 DAT. Residues of 7-hydroxyfuro[3,4-b]pyridine-5(7H)-one and 2,3-pyridinecarboxylic acid were also identified in all ponds (< 2.00 ppb after 14 DAT).
Because this study was performed during the summer months, the rapid dissipation observed in this study may not be representative of dissipation rates at other aquatic environments. 

 

Phototransformation in soil:

Key study (American Cyanamid Company, PD-M Volume 23-39, 1986)

The photostability of the test substance on thin-layer soil surfaces was investigated in a study equivalent to OPPTS Guideline 835.2210 to determine the photolysis rate and the chemical nature of the major photoproducts formed. The photolysis of the carbon-14 labeled test substance was studied on sandy loam soil. The compound was applied to the soil surface at a rate equivalent to 1.5 lb ae/acre, then exposed continuously for 28 days to light from borosilicate filtered Xenon-arc lamp in a custom-made environmental chamber. The soils were irradiated approximately 80 cm from the light, which was operated continuously at 6,000 watt. The light produced by the lamp is comparable to summer sunlight in Chicago, Illinois. The test substance degraded slowly on irradiated soil. There was 11% degradation of the test substance over the 28 days of continuous irradiation. None of the at least five degradation products accounted for >10% of the applied dose. The half-life under the conditions of this test was calculated to be 149 days.