Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Hydrolysis was the only endpoint assessed for stability for the submission substance.

This study determined the rate of hydrolysis of [14C]NBPT in sterile aqueous buffer systems at pH 3, 7 and 11 in the dark at 25°C. Phase 1 Tests were conducted at ~160 ppm. Phase 2 Tests were conducted at ~160 ppm for pH 3 samples and ~32 ppm for pH 11 samples. No change in the pH occurred during the Phase 2 Tests. No losses of radiocarbon occurred during the study.

[14C]NBPT was moderately stable in pH 7 solution with 18.6% of the initial concentration of [14C]NBPT hydrolyzed after 28 days. From the results of the Phase 1 Test, the first-order rate constant kh was determined to be 0.0075 day-1. The half-life of NBPT at pH 7 was calculated to be 92 days.

The rate of NBPT hydrolysis was rapid in pH 3 buffer solution. In the Phase 2 Test, all of the applied [14C]NBPT was hydrolyzed after 360 minutes of incubation at 25°C. The pseudo first-order rate constant (khvalue) for hydrolysis was determined to be 17.136 day-1. The half-life of NBPT was 58 minutes (0.040 days) in pH 3 buffer solution.

At the conclusion of the Phase 2 Test at pH 11 (28 days), 69.0% of the initial concentration of [14C]NBPT was hydrolyzed. The pseudo first-order rate constant kh was determined to be 0.0424 dail at pH 11. The half-life of hydrolysis was 16 days for NBPT in pH 11 buffer solution.

The rate constants kA, kB, and kNwere determined to be 17,130 dai1, 36.58 day-1, and 0.00581 day-1, respectively. The major products of hydrolysis were Degradates 1 and 2, which were separated and quantitated by HPLC analysis. Confirmation of [14C]NBPT was done by TLC analysis of selected samples.

The spectra indicate that Degradate 1 is N-(n-butyl)thiophosphoric diamide, formed by hydrolysis of NBPT at one of the amide substituents. The proton and 31P NMR spectra of Degradate 2 identify it as butylamine and these spectra indicate that this product is butylamine results from hydrolysis of NBPT and/or Degradate 1.

The results of this study suggest that the hydrolysis of is a substantial mode of dissipation under acidic and basic conditions and of moderate importance at neutral pH.

At 25°C,  pH=3, first order rate constant (kh) = 17.136/day, half-life = 58 minutes

At 25°C,  pH=7, first order rate constant (kh) = 0.0075/day, half-life = 92 days

At 25°C,  pH=11, first order rate constant (kh) = 0.0424/day, half-life = 16 days