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

Biodegradation in water:

An OECD 301B test showed that the test substance is not readily degradable and does not inhibit mircoorganisms at a conceentration of 10 mg/L.

Biodegradation in water and sediment: Simulation tests

Aerobic Aquatic Degradation (American Cyanamid Company, PD-M Volume 25-51, 1988): Stable

Anaerobic Aquatic Degradation (American Cyanamid Company, PD-M Volume 23-36, 1986): Stable

Biodegradation in soil

Aerobic Soil Metabolism: Stable; half-life of 5.9 years (American Cyanamid Company, 34927, 1988)

Anaerobic Soil Metabolism: Stable (American Cyanamid Company, 1990)

Additional information

Biodegradation in water and sediment: Simulation tests

Aerobic Aquatic Degradation (American Cyanamid Company, PD-M Volume 25-51, 1988)

The degradation of the test substance in an aerobic sediment/water system was evaluated in a study equivalent to OPPTS 835.4300. A sediment/water mixture was collected from a lake in central New Jersey. Samples containing 100 mL of a lake water and approximately 5 g of sediment solids were spiked with approximately 0.34 mg of 14C-labeled test substance (corresponding to an application rate of 1.5 Ib/acre). The samples were incubated in the dark under aerobic conditions at 25±1 °C.

Recoveries of the test substance at all time points were quantitative. Less than 1% of the applied radioactivity remained in the soil marc after extraction. No volatile organic compounds were detected, and only a small amount of 14CO2 was trapped. Almost all (>95%) of the test substance remained in the aqueous phase of the samples. No measurable degradation of the test substance occurred during the one month experiment. Thus, the test substance appeared to be stable under aerobic aquatic conditions.

Anaerobic Aquatic Degradation (American Cyanamid Company, PD-M Volume 23-36, 1986)

The degradation of the test substance in an anaerobic sediment/water system was studied equivalent to OPPTS 835.4400. The sediment/water mixture was collected from a lake in a forested region in central New Jersey. Measurement of the initial sediment voltage indicated that the sediment was anaerobic (0 to -50 mV relative to the standard hydrogen electrode). 14C-labeled test substance, applied at 1.5 Ib/acre, was incubated in an anaerobic sand sediment:water system in the dark at 19-22 °C for up to 3 months. The test substance comprised 96-98% of the recovered radioactivity at all sampling intervals. No measurable degradation of the test substance occurred during the experiment with approximately 70% of the test substance remaining in the aqueous phase. Thus, the test substance appeared to be stable under anaerobic aquatic conditions.

Additionally, an aerobic degradation study with two degradation products of the test substance, which were studied in each of two pond water/sediment systems, is available (American Cyanamid Company, E-98 -018, 1999). The study was performed with the two degradation products: Furo[3,4 -b]pyridine-5(7H), one-7-hydroxy and pyridine 2,3-dicarboxylic acid. A pond water/sediment system (water pH 8.2, sand sediment pH 7.7, organic matter 0.8%) from Florida, and a pond water/system (water pH 7.9, silt loam sediment 6.6, organic matter 1.1%) from Missouri were studied at 25±1 °C in darkness for a 14-day period. The 14C-labelled degradation products of the test substance were applied onto the water surface separately at a nominal rate of 0.083 ppm.
As a result, furo[3,4 -b]pyridine-5(7H), one-7-hydroxy was rapidly converted into pyridine 2,3-dicarboxylic acid in the water layer of both the Florida and Missouri pond systems with half-life values of 2 to 3 days. Pyridine 2,3-dicarboxylic acid also degraded rapidly with half-life value of 2 days in the water phase of both the Florida and Missouri pond system.
The study showed that both test substance photoproducts are rapidly degraded in aquatic systems. Both compounds are converted to nicotinic acid which is further degraded, via ring opening, to naturally-occurring volatile and small organic compounds, such as acetic acid and pyruvic acid, and CO2. Thus, furo[3,4 -b]pyridine-5(7H), one-7-hydroxy and pyridine 2,3-dicarboxylic acid are not expected to persist when formed in the environment..

Biodegradation in soil

Key study: Aerobic Soil Metabolism (American Cyanamid Company, 34927, 1988)

The aerobic soil metabolism of the test substance was evaluated in a laboratory test equivalent to OPPTS 835.4100. 14C/13C-labeled test substance was added to Princeton sandy loam soil (soil moisture 75% of filed capacity) at a concentration of 1.5 ppm. Samples were maintained at 25 °C in the dark for up to 365 days.

Volatiles and/or CO2 were collected in traps. At 365 days, 88% of the applied radioactivity remained as parent test substance. An apparent half-life of 5.9 years was calculated for the test substance under aerobic test conditions in sandy loam soil. Five unknown degradates were observed intermittently during the study. None accounted for greater than 1.3% of the initial applied dose (IDA). Unextractable residues averaged 4% of the applied radioactivity during the study and accounted for 5% at 365 days. Cumulative 14CO2 accounted for up to 7% of the applied radioactivity after 365 days. 14C-labeled test substance accountability at day 365 was 91.5% of IDA while the average for the study to date was 101% of IDA.

In conclusion, the test substance is essentially stable to degradation in soil maintained under aerobic conditions.

 

Supporting study: Aerobic Soil Metabolism (American Cyanamid Company, ENV 98 -029, 1999)

A supporting aerobic soil metabolism study, conducted over a period of 121 days in sandy loam soil from New Jersey, is available. The study was performed using 14C-labeled test substance with the radiolabel in the 6-carbon of the pyridine ring. The test compound was applied to the soil at an initial application rate of 0.22 ppm. The soil was maintained aerobically in the dark at 25±1 °C for up to 4 months at 75% of 1/3 bar moisture. Because the 121-day study period was short compared to the persistence of 14C-labeled test substance, there was insufficient time for the full pattern of formation and decline of products to develop.

Material balance ranged from approximately 100% to 97%. Approximately 0.1-0.2% of the radioactivity was accounted as unextracted residues at 0-time and this value increased to approximately 6-6.1% after 4 months of incubation. After 4 months of incubation, there was approximately 5.6% of the total applied radioactivity has been evolved as 14CO2 indicating that the test substance is mineralized in soil. There were no detectable levels of organic volatiles in the ethylene glycol traps. Approximately 26% of the test substance was degraded after 121 days of aerobic incubation. The first-order degradation half-life was calculated to be 313 days. The rate of degradation of the test substance decreased after 1 month of incubation and appeared to be a biphasic pattern with transition point at approximately 28 days. Using the first month degradation data only, the half-life of the test substance in soil was calculated to be 117 days. The half-life in the second phase was 438 days.

A structurally similar transformation product, 2 -(4 -isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-3-hydroxy pyridine, was present at approximately 6.4% of parent radioactivity recovered at the beginning of the study. Two additional minor transformation products, 2-[(1-carbamoyl-1,2-dimethylpropyl)carbamoyl] nicotinic acid and 2 -(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-3-carboxymethyl pyridine, were each detected at 2.1 and 2.3% of the applied dose.

 

Supporting study: Anaerobic Soil Metabolism (American Cyanamid Company, PD-M Volume 20-15, 1983)

The anaerobic soil metabolism was evaluated in a laboratory test equivalent to OPPTS 835.4200. Sandy loam was treated with a 50:50 mixture of 14C and 13C-carboxy-labeled test substance at 1 Ib ae/acre (1 ppm) and maintained under anaerobic conditions, after aging aerobically for one month. The test substance was stable in sandy loam soil and thus no half-life was calculated. The total radioactivity recovered at one and two months was 109.4% and 107.6%, respectively. The radioactivity in the water extract was three-fold that in the soil after 2 months.

In conclusion, C14-labeled test substance in Princeton sandy loam was not metabolised under the anaerobic conditions studied.