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Environmental fate & pathways

Biodegradation in soil

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There is no literature available for the degradation of NPPT in soil. NBPT was considered to be a suitable analog to NPPT because NBPT has similar modes of action, differ structurally only in one methylene group and are subject to similar degradation and metabolism processes.

Therefore, a publication by Hendrickson and Douglass (1993) has been consulted, which investigated the disappearance of NBPT from different silt loam soils and its transformation to the active but more unstable analog BNPO (N-(n-butyl)phosphoric triamide). After normalization of the DT50 values to 20°C, a half-life time in soil of 3.1 days could be determined for NBPT. This half-life time was obtained calculating the geometric mean of all DT50 values derived from the three soil types and different application rates of NBPT (soil 1: 10 mg/kg, soil 2: 1, 10 and 100 mg/kg, soil 3: 10 mg/kg). The retrieved DT50 value of 3.1 days can be seen as a worst case degradation scenario since common application rates of the product are situated even below the lowest NBPT application rate of 1 mg/kg soil of the study.