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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

TNPP has not found to be readily biodegradable in two separate OECD 301 studies. In one study 4% of TNPP was found to  degrade after 28 days and in another study 1% of TNPP degraded after 29 days.

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable

Additional information

The ready biodegradability of TNPP was studied in both a closed bottle test (OECD 301D) test (Guterson, 2001) and a CO2

301B (CIBA-Geigy, 1994).

In the OECD 301D study, TNPP solutions were inoculated with a commercial bacterial preparation (Polyseed) and incubated at 20 ± 1°C.

The biological oxygen demand (BOD) of the test substance was measured at 0, 7, 14, 21 and 28 days and compared to the theoretical oxygen demand (ThODNO3) of the nominal concentration of TNPP. TNPP concentration was 15.4 mg.L-1which was theoretically corresponding to a Chemical Oxygen Demand of 13.2 mg. Beside the TNPP solution, there were 3 controls: a test control (inoculated mineral medium), a procedure control (degradation of a reference substance) and a toxicity control (degradation of the reference substance in the simultaneous presence of TNPP). All controls passed the acceptability criteria of the test: oxygen depletion in the test control did not exceed 1.5 mg per litre after 28 days incubation, biodegradation of the sodium acetate reference substance met the criterion of > 60% of the ThODNO3within 14 days. TNPP did not inhibit the degradation of the reference substance by more than 25% after 14 days. Finally, the variance amongst duplicate test bottles was less than 20%. Less than 4% of TNPP was biodegraded after 28 days experiment.

In the OECD 301B study, TNPP was tested at a concentration of 18.1 mg/L which corresponds to 15.3 mg ThOC/L. The inoculum was constituted with activated sludge collected from the sewage treatment plant of Reinach (Switzerland). The pH after collection was 7.0. Before application, the inoculum was pre acclimated to the test medium overnight. The test was performed at a temperature of 22 +/- 2°C with a carbon dioxide free air supply. To take into account the very low solubility of the test substance, its preparation was as follow: a stock solution was prepared dissolving 1.36 g. of test substance in 10 mL dichloromethane. From this stock solution, for each replicate, 27.2 mg (200 µL) were applied onto a filter paper as small drops. After the filter paper was completely dry (no remaining of dichloromethane was present), it was cut to small pieces (10-15) and added to the test medium. Thereafter, the medium volume was completed to 1.5L with 300 mL water and the flasks were immediately connected to the CO2scrubber. Within a few hours the filter paper was homogeneously distributed in the test medium (so that it could not be seen anymore). Only 1% of TNPP was biodegraded after 29 days experiment.