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

Biodegradation in water and sediment: simulation tests

Description of key information

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

Additional information

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.

The mean recovery of the test substance at all time points were 99.5 % of applied radioactivity. Less than 1% of the applied radioactivity remained in the soil after extraction. Almost all (>95%) of the test substance remained in the aqueous phase of the samples. and thus, no volatile organic compounds were detected, and only a small amount of 14CO2 was trapped.

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.