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Environmental fate & pathways

Biodegradation in water: screening tests

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Administrative data

biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP study following current guideline.

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
1 minor deviation; the omission of ammonium chloride from the medium to prevent oxygen consumption due to nitrification
GLP compliance:

Test material

Constituent 1
Chemical structure
Reference substance name:
Triphenyl phosphite
EC Number:
EC Name:
Triphenyl phosphite
Cas Number:
Molecular formula:
triphenyl phosphite
Test material form:
other: liquid
Details on test material:
Test material supplied by Addivant USA LLC
Batch: MW4K25B801
>99% purity
<1% phenol impurity

Study design

Oxygen conditions:
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Obtained from wastewater treatment plant Nieuwgraaf in Duiven, Netherlands The plant treats predominantly domestic wastewater. The activated sludge was preconditioned to reduce the endogenous respiration rates by aeration for one week.
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
2 mg/L
Based on:
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The Closed Bottle test was performed according to the study plan. The study plan was developed from ISO Test Guidelines (1994). Use was made of 10 bottles containing only inoculum, 10 bottles containing inoculum, silica gel and test substance, 10 bottles containing inoculum, and silica gel, and 6 bottles containing sodium acetate, and inoculum. The concentrations of the test substance, and sodium acetate in the bottles were 2.0, and 6.7 mg/L, respectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles were closed and incubated in the dark. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.
Reference substance
Reference substance:
acetic acid, sodium salt

Results and discussion

Preliminary study:
Results of a preliminary study lead to the use of activated sludge with silica carrier agent.
Test performance:
Triphenyl phosphite is biodegraded by 84% at day 28 in the Closed Bottle tes). Over 60% biodegradation was achieved after approximately 6 days immediately
following the attainment of 10% biodegradation. The test substance therefore fulfilled the time window criterion for ready biodegradable substances. Hence, the test substance is classified as readily biodegradable.
% Degradationopen allclose all
% degradation (O2 consumption)
Sampling time:
7 d
% degradation (O2 consumption)
Sampling time:
14 d
% degradation (O2 consumption)
Sampling time:
21 d
% degradation (O2 consumption)
Sampling time:
28 d

Any other information on results incl. tables

Theoretical oxygen demand (ThOD)

The calculated theoretical oxygen demand (ThOD) of triphenyl phosphite is 2.2 mg/mg. The ThOD of sodium acetate is 0.8 mg/mg


Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of triphenyl phosphite to microorganisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the inoculum by the test substance at day 7 was not detected . Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.

Test conditions

The pH of the media was 7.3 at the start of the test. The pH of the medium at day 28 was 7.3 (both controls), and 7.1 (test). Temperatures were within the prescribed temperature range of 22 to 24°C.

Validity of the test

The validity of the test is demonstrated by an endogenous respiration of 0.9 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 83%. Finally, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Applicant's summary and conclusion

Validity criteria fulfilled:
The validity of the test is demonstrated by an endogenous respiration of 0.9 mg/L at day 28 (Table I). Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference compound, sodium aceta
Interpretation of results:
readily biodegradable
The results of the study show TPP is readily biodegradable meeting both the overall and 10-window criteria.
Executive summary:

TPP was 84% biodegradable in a 28 -day ready biodegradation study using OECD 301D (closed bottle test). The results also passed the 10 -day window of 60% biodegradation during the first week of the study. TPP will be classified as readily biodegradable based on these results.