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Toxicity to microorganisms

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activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study, but study details not readily available.
Justification for type of information:
Read Across to an analogue based on structural similarity. An analogue justification is attached to section 13 of the dataset.
Reason / purpose for cross-reference:
read-across: supporting information
according to guideline
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
Analytical monitoring:
not specified
Details on test solutions:
2000 mg in 500 ml Ethanol.
Test organisms (species):
activated sludge
Test type:
not specified
Total exposure duration:
30 min
Nominal and measured concentrations:
Highest tested concentration amounted to 1003 mg/l
Reference substance (positive control):
not specified
30 min
Dose descriptor:
other: EC20
Effect conc.:
650 mg/L
Validity criteria fulfilled:
not specified
The EC20 was determined to be 650 mg/L after 30 minutes.

activated sludge respiration inhibition testing
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is found to be readily biodegradable and the applied test concentrations are in the range of concentrations that can be expected in the influent of a sewage treatment plant

Description of key information

There are no toxicity to microorganism studies with the test substance tin bis(2-ethylhexanoate). Data from OECD 209 study with
tin(II)methanesulfonate was used.

Read-across, OECD 209, static, 3h: EC50 113.62 mg/L and EC10 39.9 mg/L calculated for the target substance


Key value for chemical safety assessment

EC50 for microorganisms:
113.62 mg/L
EC10 or NOEC for microorganisms:
39.9 mg/L

Additional information

There are no toxicity to microorganism studies with the test substance tin bis(2-ethylhexanoate). This endpoint is waived in accordance with column 2 of REACH Annex VIII, which states that the activated sludge respiration inhibition testing (Required in section 9.1.4) does not need to be conducted if the substance is found to be readily biodegradable. Tin bis(2-ethylhexanoate) is readily biodegradable and the concentrations which were tested in the biodegradation screening tests are orders of magnitude higher than could be realistically expected in a STP influent, based on known use scenarios. As no apparent inhibition of the inocula was observed in the biodegradation screening tests, it can be assured that concentrations equal to or lower than those tested in the biodegradation screening tests would have no adverse impact on respiration or viability of the STP microorganisms.


In order to calculate a PNECSTP, a sludge respiration inhibition test on tin(II)methanesulfonate was considered:

The effect of tin(II)methanesulfonate on the respiration rate of an activated sludge according to the OECD Guideline 209 and EC Method C.11 under GLP was investgated. The test item was given to the synthetic sewage with a concentration of 43, 94, 207, 455 and 1000 mg test item per liter. The content was aerated for 3h at 20 +/- 2 °C. Twi replicates were prepared for controls (synthetic sewage and inoculum only), solitaire vessels were used for treated assays. The results show, that at a concentration of 43 mg test item per liter, no respiration inhibition occurred (assessed as NOEC). At a concentration of 94 mg/L, the test item inhibited the respiration of the inoculum (respiration rate of 26.2 mg O2/(L*h)). Due to a respiration rate below the range of the control assays (29.3 - 30.1 mg O2/(L*h)), the concentration of 94 mg/L is assessed as LOEC. At a concentration of 1000 mg/L the inhibition was about 96%.

There is a significant inhibition of bacteria respiration starting at a concentration of 94 mg/L. For the respiration rate the EC50 is 299 mg/L, the EC10 was reported with 105 mg/L for the source substance. Referred to the Sn amount in the Target substance and the molecular weight the EC50 is calculated to be 113,6 mg/L and the EC10 39,9 mg/L, respectively.