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Environmental fate & pathways

Biodegradation in soil

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Description of key information

1) Key: Biodegradation in soil with one of the constituents of DAPD (R-898; CAS 15017-02-4), K1, GLP, according to USEPA guideline, indicative of strong binding behaviour to soil

Key value for chemical safety assessment

Half-life in soil:
66.5 d

Additional information

There is one test available that describes the environmental fate in soil of one of the main constituents of 1,4 -benzenediamine, N,N’-mixed Ph and tolyl derivs (R-898; CAS 15017 -02 -4)(McLaughlin, 1997). It regards a terrestrial field soil dissipation test in which 14-C labelled N,N’-bis(2-methylphenyl)benzene-1,4-diamine (CAS 15017 -02 -4) is added onto the top surface of soil cylinders of 8 inches in diameter.

The use of the N,N'-di-o-tolyl-p-phenylenediamine component as surrogate for the submission substance is based upon its structural similarities to other components of the submission substance 1,4-benzenediamine, N,N'-mixed Ph and tolyl derivs. This component was selected based upon its availability as radioactive material plus modelling results indicate it to be least susceptible to biodegradation, providing worst-case outcome for the submission substance. Soil samples were collected over a period of 362 days post application. Four measurements were made on each soil sample: total 14-C, solvent extractable 14-C, unextractable 14-C, and the extract fraction was checked on its test substance content. The extractable levels of test substance and total extractable radioactivity both showed a strong decrease on day 362.

More specifically, the test results demonstrated that most (~98%) of the 14-C labelled material remained in the top 3 inches of the soil. In total, 46% of the applied radioactivity was present in the top soil layer after 362 days, suggesting that 54% is lost due to volatilization or degradation. Migration below the 3 inch level was shown to be minimal. The amounts of recovered test substance as % of the total radioactivity present in the top 3 inches level at the study’s initiation and termination where 49 and 0.7%, respectively. Unextractable 14-C increased from 43% on day 0 to 91% on day 362. The DT50 appear to be 10.8 days (calculated over exposure duration day 0 to day 32) and 66.5 days (calculated over exposure duration from day 0 to day 362)The results indicate that the test compound or its degradate(s) strongly binds to soil, thus attenuating its potential bioavailability as well as its migration from soil to ground water.