Dibutyltin oxide

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

December 6, 2002 to January 15, 2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): oxidation ditch in Hazerswoude, the Netherlands, on 3 December 2002
- Storage conditions: Transported in a plastic flask and aerated until use
- Storage length: 3 days
- Preparation of inoculum for exposure:
- Pretreatment:
- Concentration of sludge: solids in test flask = 100 mg (dw)/l
- Initial cell/biomass concentration:
- Water filtered: yes
- Type and size of filter used, if any: Whatman GF/C 0 47 mm

Duration of test (contact time):

28 d

Initial conc.:

34.3 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Remarks:

oxygen consumption due to the test or control substance at each time was calculated by subtracting the mean cumulative oxygen consumption in the blanks from that in the flask under consideration

Details on study design:

One mean concentration of 34.3 mg/l was tested, corresponding to a Theoretical Oxygen Demand (NH3) of 52.8 mg 02/l. An inoculum was prepared from activated sludge taken from an oxidation ditch used to treat domestic sewage (100 mg dw/l). There were 3 replicate flasks and oxygen concentration was determined every 5 hours. The inoculum activity control had a reference substance of 0 and 100 mg/L, 3 blank flasks and 2 replicates for the 100 mg/L control. The toxicity control reference substance was 100 mg/L in 2 replicate flasks. Oxygen concentration for the controls were determined every 5 hours.

Reference substance:

other: sodium acetate, anhydrous

Preliminary study:

Dibutyloxostannane was not biodegraded after 31 days. In this study, the 60% degradation criterion after 28 days was not met, and therefore the test substance was considered not readily biodegradable.

Test performance:

The test met the conditions of validity set forth by the OECD Guideline 301F and the EU Test Guideline C.4-D (similar to EPA Guideline OPPTS 835.3110).

Parameter:

% degradation (O2 consumption)

Remarks:

manometric respiration

Value:

0

Sampling time:

28 d

Details on results:

Table 2 shows the relevant mean Biochemical Oxygen Demand values and the percentage biodegradation of dibutyloxostannane at a concentration of 34.3 ± 3.9 mg/l, calculated from the ThOD NH3 (1.54 mg O2/mg) of the test substance.

The percentage of degradation of dibutyloxostannane after 28 days of incubation did not exceed 0% in a manometric respiration test at a concentration of 34.3 ± 3.9 mg/l, calculated from the ThOD NH3 (1.54 mg O2/mg) of the test substance. The biodegradation of dibutyloxostannane did not exceed the pass level of 60% THoD NH3 within 28 days, and therefore is classifed as "not readily biodegradeable".

Results with reference substance:

The conditions of validity have been met as follows:
- The amount of oxygen consumed in the biodegradation test is so low, that this criteria has little relevance. However, the extreme replicate cumulative oxygen consumption values for the inoculum toxicity and activity control varied less than 20% at the end of the test.
- The reference substance was degraded 99% (ThOD) within 14 days.
- The degradation in the toxicity control was above 25% during the test.
- The oxygen consumption in the blanks with filter was 1.21-2.96 mg per flask after 28 days of incubation, which is equal to 4.0-9.9 mg/L, which is within the limits of validity.
- The pH remained within the valid range during the test in the blank and control tests.

Table 2. Biodegradation of dibutyloxostannane (34.3 ± 3.9 mg/L)
expressed as the BOD (mg O2/mg) and as percentage of its ThOD NH3 (mean values, n=3)
Time (days)	BOD (mg O2/mg)	% Biodegradation (ThODNH3)
14 (336 hours)	0	-2
28 (680 hours)	0	-2
31 (755 hours)	0	-2

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

The percentage degradation of dibutyloxostannane after 28 days of incubation did not exceed 0% in a manometric respiration test at a mean test substance concentrations of 34 ± 3.9 mg/l calculated from the ThOD NH3 (1.54 mg O2/mg) of test substance. The biodegradation of dibutyloxostannane did not exceed the pass level of 60% ThOD NH3 within 28 days and, therefore, is classified as not readily biodegradeable. Dibutyloxostannane is not toxic to the inoculum, but a slight inhibitation of the degradation of the reference substance was observed.

Executive summary:

The test medium was added directly to a glass fibre filter and the filter was placed in the mineral test medium. The concentration tested was 34.3 ± 3.9 mg/L, corresponding to a ThOD NH3 of 52.8 ± 6 mg O2/L. An inoculum was prepared from activated sludge taken from an oxidation ditch used to treat domestic sewage. The test met the conditions of validty given by the guidelines. The test material was not biodegraded after 31 days. The 60% degradation criterion after 28 days was not met and therefore the test substance was considered to be not readily biodegradable. Dibutyloxostannane is not toxic to the inoculum, but a slight inhibition of the degradation of the reference substance was observed.

Description of key information

The following study is available to address the biodegradation in water endpoint:

Hanstveit, R. (2003). Dibutyloxostannane (Dibutyltin oxide, CAS No. 818-08-6): Determination of the ready biodegradability in a Manometric Respiration Test. Testing laboratory: TNO, Department of Biomolecular Sciences, Utrechtseweg 48, P. O. Box 360, 3700 AJ Zeist, The Netherlands. Report no.: V4016/01. Owner company: Organotin Environmental Programme (ORTEP) Association represented by Paramtrix Inc., 5808 Lake Washington Blvd. NE, Suite 200, Kirkland, WA 98033-7350. Study number: project no: 010.46080.01.08. Report date: 2003-09-24.

The study has been allocated a Klimisch score of 1 and is the key study for this endpoint.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

The study Hanstveit R (2003) was included as the key study for this data requirement as it was performed to the OECD guideline 301 F and in compliance with GLP. The study was therefore assigned a reliability score of 1 and considered suitable for assessment. In a ready biodegradability study (OECD 301F) 0% biodegradation was observed after 28 days. DBTO is therefore defined as not readily biodegradable.