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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

NOEC = 1000 mg/L

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

An experimental study for the determination of the toxicity of B-TTEGME to microorganisms is not available. QSAR analysis was not performed since "the use of QSARs for predicting STP toxicity is still limited. Although there are some QSARs for toxicity to microorganisms published...., this is not a very well developed science domain today." (Guidance on information requirements and chemical safety assessment, Chapter R.7B: Endpoint specific guidance, section R., page 136). However, there is sufficient information from read across and a study with a B-TTEGME containing Brake Fluid to perform the risk assessment as outlined below.

B-TTEGME is mixture of different borated glycol esters. The length of the glycol ester moiety ranges from 3 to 5 glycols per glycol ester moiety. About 50 % of B-TTEGME have a chain length of 3 glycols per glycol ester moiety. The molecule with the chain length of 3 glycol esters is registered under the name B-TEGME (cas# 30989 -05 -0). Therefore, B-TEGME is relevant for the risk assessment of B-TTEGME.

Following information is available for B-TEGME.

In the GLP compliant study from BASF (1999) the effect of B-TEGME on the oxygen consumption of activated sludge was determined in a limit test with 1000 mg B-TEGME/L. The study is considered compliant with OECD 209, ISO 8192 and C.11. The inoculum was obtained from laboratory wastewater plants treating municipal waste water. The inoculum was washed, adjusted to 5g dry mass/L and subsequently aerated for 24 hours. Three controls and one replicate for the treated test solution was set up. Non-replicated positive controls were set up with 1, 10 and 100 mg 3,5 -dichlorophenol/L The respiration measurements were performed 30 minutes after start of the exposure.

The test with 3,5 -dichlorophenol resulted in an EC50 of 8.8 mg 3,5 -dichlorophenol/L. The variation between 3 controls was < 15%. The findings from the positive controls render the test as valid. At 1000 mg B-TEGME/L, the respiration was increased by 6% relative to the average respiration in the control. Therefore, the EC0 is 1000 mg B-TEGME/L and the EC20, EC50 and EC80 are > 1000 mg B-TEGME/L and consequently B-TEGME is considered to have no effect on microorganisms.

In the GLP compliant study from Shell (1986), the microbial inhibition of a brake fluid (which contains 35% B-TTEGME) to Pseudomonas fluorescens was determined in a microbial inhibition test. The test design was based on the method described in "Degradability, Ecotoxicity, and Bioaccumulation, TNO, Delft, The Netherlands, 1977". The nominal test concentrations were 0 (Control), 10, 32, 100, 320, and 1000 mg brake fluid/L (nominal concentrations), corresponding to 0 (control), 35, 11.2, 35, 112, and 350 mg B-TTEGME/L, respectively. Sodium pentachlorophenate was used as positive control. Growth curves were constructed of the optical density of the inoculated media versus time and the rate determined as the slope of the exponential growth phase. The reference substance, sodium pentachlorophenate inhibited with an EC50 =18 mg/L while the brake fluid caused a maximum of 19% inhibition at 1000 mg brake fluid/L, corresponding to 350 mg B-TTEGME/L, the highest concentration tested. Therefore, the EC50 is > 350 mg B-TTEGME/L. The exposure duration, environmental conditions like temperature and details on the measurements of the optical density and the origin of the cultures were not reported. Due to the limited information provided the results of this study are considered to have only limited relevance and the study was considered to be supporting.

The GLP study with B-TEGME (BASF, 1999) provided an EC10 and EC50 of > 1000 mg B-TEGME/L. The advantage of this study is that it was performed with B-TEGME itself and not with a B-TTEGME containing brake fluid as in the study from Shell (1986) where other additives may affect microbial growth. The (supporting) study from Shell (1986) provided an EC50 of > 395 mg B-TTEGME/L, the highest tested concentration. Due to the above restrictions the test results from Shell (1986) were not considered as relevant for the risk assessment. In conclusion, the EC10 and EC50 values of >1000 mg B-TEGME /L are considered reliable and sufficiently conservative to assess the toxicity of B-TEGME on microorganisms.

For following reasons the study from BASF (1999) on B-TEGME is considered to give sufficient indication for the assessment of the toxicity of B-TTEGME to microorganisms:

  • B-TEGME is with about 50% the major constituent of B-TTEGME, i.e., B-TEGME as part of B-TTEGME is already investigated
  • B-TEGME is not toxic to microorganisms at 1000 mg B-TEGME/L
  • B-TEGME and B-TTEGME are both not toxic to aquatic organisms, both substances are readily biodegradable and furthermore, biodegradation studies gave no indication that one of the substances is toxic to microorganisms. Hence there is no evidence that B-TTEGME is more toxic than B-TEGME
  • B-TTEGME constituents other than B-TEGME are characterised by the longer chain length (additional 1 or 2 glycol esters per chain) when compared to B-TEGME
  • from glycol esters it is known that the toxicity of glycol esters decreases with increasing chain length

Based on the above considerations, there is no indication that B-TTEGME may be more toxic to microorganisms than B-TEGME. Consequently, a NOEC of 1000 mg B-TTEGME/L is used for the risk assessment of B-TTEGME.