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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Data are available from a similar substance 7PPD.
Aerobic conditions: The metabolism of 14C-7PPD in aerobic soils is proposed to proceed via formation of minor transient metabolites and mineralization. The main portion of the residue is binding to the soil matrix and appears to become unavailable for further degradation/mineralization. DT50 values of the parent, derived from FOMC (First-Order Multi Compartment kinetics), were 1.4 – 1.9 days for Soils II-IV and < 1 day for soil I.
Anaerob conditions: The rapid decline of 7PPD in the initial aerobic phase was likely to extend into the anaerobic phase of the test system given, that the transition to anaerobic conditions by soil flooding is progressive. Therefore, the short DT50 of 7PPD (1.5 days) in the flooded test system was attributed to aerobic degradation. Following that rapid initial decline, the parent dissipated slowly, from 23.2% AR on day 1 to 17.0 AR on day 120.

Key value for chemical safety assessment

Half-life in soil:
1.9 d
at the temperature of:
12 °C

Additional information

Aerobic conditions:

DT50 values derived from First Order Multi Compartment kinetics (FOMC) kinetics were 1.4 – 1.9 days for Soils II-IV and < 1 day for soil I. The faster decline in acid soil I (pH 3.8) was explained by the instability of 7PPD under acidic conditions.

The metabolism of 14C-7PPD in aerobic soils is proposed to proceed via formation of minor transient metabolites and mineralization.The main portion of the residue is binding to the soil matrix and appears to become unavailable for further degradation/mineralization.

Anaerobic conditions:

The short DT50 of the parent (1.5 days) in the flooded test system was attributed to aerobic degradation. Following that rapid initial decline, 7PPD dissipated slowly. A DT90 of >1000 days was calculated. The metabolite 1-N-(5-methyl-hexan-2-yl)-4-N-phenylcyclohexa-2,5-dione-4,4-diimine also known as 7QDI, (cis/trans isomers) was observed.

7QDI Isomer 1: DT50 = 57.9 d; DT90 = 192 d

7QDI Isomer 2: DT50 = 79.7 d; DT90 = 265 d

7QDI Isomer 1+2: DT50 = 66.9 d; DT90 = 222 d

Degradation was described by SFO (Single First Order) model.

Justification for the read-across:

1,4-Benzenediamine, N-(1,4 -dimethylpentyl)-N'-phenyl- ("7PPD") has a similar structure as 6PPD. It is a member of the paraphenylene diamine family. The difference is that 7PPD has an C7 branched aliphatic chain, whereas 6PPD has C6 branched aliphatic chain. Additional information on the read-across is given in the read-across-justification document attached to IUCLID chapter 13.