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Environmental fate & pathways

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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