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Toxicity to aquatic algae and cyanobacteria

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Description of key information

ErC50 > 224.4 mg/L
NOEC = 224.4 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
224.4 mg/L
EC10 or NOEC for freshwater algae:
224.4 mg/L

Additional information

For the assessment of the EC50 for freshwater algae, three studies are available, one key study conducted with methyl borate esters containing 22% B-TEGME (Shell 1999a), one supporting study with B-TEGME (BASF 1989) and one supporting study with a brake fluid which contains 17% B-TEGME (Shell 1987b).

In the GLP compliant (key) study from Shell (1999) the growth inhibition of methyl borate esters (containing 22% B-TEGME) to Pseudokirchneriella subcapitata was determined in a 72 h static algae growth inhibition limit test according to EU Method C.3 and OECD 201. No relevant restrictions appeared and the only disadvantage of this study is the fact that the study was performed with a B-TEGME containing mixture and not with B-TEGME as pure substance itself. The nominal test concentrations were 0 (control) and 1000 mg methyl borate esters/L (= 220 mg B-TEGME/L). The mean measured concentration was 1020 mg methyl borate esters/L corresponding to 224.4 mg B-TEGME/L. During the study, the pH increased by more than 1 unit at the end of exposure, which is a deviation to the C.3 and OECD 201 guidelines. Since the control cultures showed exponential growth through the 72 hour exposure period and the growth rates of the control cultures fulfilled the validity criteria from OECD 201 (2006), this deviation is considered to have no effect on the general outcome of the study. After 72 hours of exposure, the AUC of the treated test group (224.4 mg B-TEGME/L) was 16 % higher than the control. After 72 hours of exposure, the average specific growth rate of the treated test group was 9.4% higher than the control. Based on these results, the NOEC for AUC and growth rate was =224.4 mg B-TEGME/L. The 72 -hour EbC50 and ErC50 were both > 224.4 mg B-TEGME/L.

In the non-GLP (supporting) study from BASF (1989), the growth inhibition of B-TEGME to Desmodesmus subspicatus was determined in a 72 h static algae growth inhibition test. The test design was similar to OECD 201. Restrictions of the study are: (1) the study was conducted non-GLP, (2) the purity of the test item was not stated, (3) the test design was not based on a specific test guideline, (4) many relevant details of test material and test design were not provided. (5) the pH increased by more than 1 unit at the end of the exposure (6) dose verification analysis was not performed. The nominal test concentrations were 0 (control), 7.812, 15.625, 32.25, 65, 125, 250, and 500 mg B-TEGME/L. In order to determine the growth of the cultures, fluorimeter measurements were made at 0, 24, 48 and 72 hours. No correlation between fluorimeter readings and cell concentrations was given. Since the control cultures showed exponential growth (based on fluorimeter readings) through the 72 hour exposure period and the growth rates of the control cultures fulfilled the validity criteria from OECD 201 (2006), the pH deviation is considered to have no effect on the general outcome of the study. The effect parameters were based on fluorimeter readings and nominal concentrations. After 72 hours of exposure, the EC20 and EC50 were 211.8 and > 500 mg B-TEGME/L, respectively.

In the GLP compliant (supporting) study from Shell (1987b) the growth inhibition of a brake fluid (which contains 17% B-TEGME) to Pseudokirchneriella subcapitata was determined in a 96 h static algae growth inhibition test. The test design was not based on a specific test guideline, but the provided details were similar to the OECD 201. Restrictions of the study are: (1) The treated test solutions were not replicated, (2) in combination with the lack of replication, the spacing of 2 to 2.5 is deemed to be too high to result in reliable results, (3) dose verification was not performed, (4) counting of algal cells in 48 instead of 24 hour intervals, (5) the test design deviates in many aspects from a more modern test design. The nominal test concentrations were 0 (control), 1, 2, 5, 10, 20, 50, 100, 200, 500 and 1000 mg brake fluid/L, corresponding to 0 (control),0.17, 0.34, 0.85, 1.7, 3.4, 8.5, 17, 34, 85, and 170 mg B-TEGME/L. In order to determine the growth of the cultures, cell counts were performed at 0, 48 and 96 hours. Beside the fact that the cell counts were not performed in 24 h intervals and the validity criteria from OECD 201 cannot be strictly applied, control cultures basically fulfilled the validity criteria from OECD 201 (2006). The 96 -hour EC50 was 73.1 mg B-TEGME/L corresponding to 430 mg brake fluid/L . Due to the deviation from the modern test design of algae growth inhibition tests, this study is considered to have only limited relevance. Major criticism points are the counting of algal cells in 48 instead of 24 hour intervals and the lack of replication of the treated test solutions. The guideline allows to perform the test with less than 3 replicates/test group if the aim of the study is the determination of the ECx-values. However, for this approach the spacing of 2 to 2.5 is deemed to be too high to result in reliable results.This is reflected by the very wide 95% C.I. of the effect concentrations.

The GLP (key) study from Shell (1999) was a guideline compliant study and was therefore selected as key study. The EC50 from this study was >224.4 mg B-TEGME/L.

The non-GLP (supporting) study with B-TEGME (BASF, 1989) provided an EC50 of > 500 mg B-TEGME/L, The advantage of this study is that it was performed with B-TEGME itself and not with a B-TEGME containing mixture. However, due to the above restrictions, the EC50 of BASF (1989) is considered less reliable than the EC50 of Shell (1999). Furthermore, the EC50 reported by Shell (1999) is more conservative.

The study from Shell (1987b) provided an EC50 of 73.1 mg B-TEGME/L. Due to the above restrictions the test results from Shell (1987b) were not considered as relevant for the risk assessment.

In conclusion, the NOEC of 224.4 mg B-TEGME/L and the EC50 value of >224.4 mg B-TEGME /L are considered reliable and sufficiently conservative to assess the toxicity of B-TEGME on algae.

The EC50 for freshwater algae used for the further risk assessment is 224.4 mg B-TEGME/L.

This value is higher than the limit for classification and labeling, i. e., higher than 100 mg B-TEGME/L.