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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The basis for the adoption of a category approach for the three grades of processed Cashew Nutshell Extract is the commonality of the constituents and functional groups in the three grades and the common modes of action for specific localised endpoints that are manifest in physico-chemical, environmental fate and toxicological properties that are similar or follow a regular pattern as a result of structural similarity. The ECHA Final Decisions on the Annex IX and X (mammalian toxicology, ecotoxicology and environmental fate) Testing Proposals for three grades confirmed the applicability of a category approach which involves reading data across from the source substances Cashew Nutshell Extract, Decarboxylated, Distilled (Distilled Grade) and Cashew Nutshell Extract, Decarboxylated, Distillation Residue (Distillation Residue Grade) to the target substance Cashew Nutshell Extract, Decarboxylated (Technical Grade) by interpolation. In this context interpolation is “the estimation of a value for a member of the group using measured values from other members on both sides of that member within the defined group spectrum”. Further details on the justification for using the interpolation based read-across approach are given in the attached document “Report on the grouping and read-across rationale for the three grades of processed Cashew Nutshell Extract”. The interpolation approach has been applied to the Annex IX and X OECD TG211 and TG218 testing on Distilled and Distillation Residue Grades. For the Annex VII and VIII endpoints a programme of testing has been carried out to provide comparative information for the three grades and develop a data matrix to support the category and read-across approaches. This has involved generating reliable data for all Annex VII and VIII physico-chemical and environmental fate endpoints and certain mammalian toxicity properties. However, based on the discussions surrounding the Final Decisions it was not considered necessary to apply this approach retrospectively to address all identified data gaps at Annexes VII and VIII. The original data used for the registration of a single substance (Cashew Nutshell Liquid, CAS Number 8007-24-7) was largely based on data for Distilled Grade since this was considered to be the most (eco) toxicologically active form, given the higher content of low molecular weight constituents (such as cardanol) and the low content of polymeric species. Therefore, based on the use of the category approach it is considered appropriate to read-across from the existing microorganisms toxicity data for Distilled Grade to the other two grades.
2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL)
For the toxicity to sewage treatment works microorganisms endpoint no test data is available for the registered substance, Technical Grade. However data is available for the compositionally similar substance Distilled Grade which is part of the category of the three grades of CNSL. In a 3-hour toxicity study, activated sludge was inoculated with Distilled Grade at nominal concentrations of 0, 10, 32, 100, 320 and 1000 mg/l. No signs of toxicity were noted at any concentration. The available data for the three grades indicates that they all show low measured water solubility in the range 0.2 to 0.3 mg/l. All three substances also show high measured octanol-water partition coefficients (log Kow >6.2 in all cases). This data indicates that the measured data for the key physico-chemical properties that underpin the likely short term aquatic toxicity of the three grades are consistent. On this basis it would be expected that the three grades would show similar responses in the short-term aquatic toxicity tests. This hypothesis is currently supported by the results of the results of the long-term OECD TG218 ecotoxicity test that was conducted on both Distilled Grade and Distillation Residue grade following the interpolation approach. Therefore, it is considered appropriate to read-across from the data for Distilled Grade to Technical Grade with the result that it has been estimated that there will also be no adverse toxicological effects of Technical Grade on sewage treatment works microorganisms.
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: EC20
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: EC80
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: Evidence of undissolved test material was observed at all concentrations (refer to Table 1). On some occassions, initial and final dissolved concentrations were below the recommended test guidelines (6.5 and 2.5 mg O2/l, respectively). However, this was considered to have no adverse effect on the results, given that in all cases the oxygen consumption was determined over the linear portion of the oxygen consumption trace. Relatively low initial oxygen readings were observed in the test vessels, which was possibly due to insoluble material coating the membrane of the oxygen probe. It was not possible to calculate oxygen consumption rates for concentrations of 10 and 320 mg/l due to extremely low initial and final oxygen readings. This was not considered to have any significant effect on the results, as no inhibition was observed at 32, 100 and 1000 mg/l.
Results with reference substance (positive control):
- Results with reference substance valid?: Yes
- Relevant effect levels:
- 3-hour NOEC: 2.1 mg/l
- 3-hour EC20: 2.6 mg/l
- 3-hour EC50: 8.1 mg/l (95% CL 6.3-10 mg/l)
- 3-hour EC80: 26 mg/l
Reported statistics and error estimates:
The 95% confidence limits for the reference substance EC50 were calculated using the Litchfield and Wilcoxon method.

Table 3. Oxygen consumption rates and percentage inhibition

Test material

Nominal concentration (mg/l)

Initial O2reading (mg O2/l)

Final O2reading (mg O2/l)

O2 consumption rates (mg O2/l/min)

% inhibition

Control 1

0

6.2

2.3

0.49

-

Control 2

0

3.1

1.5

0.53

-

Test item

10*

-

-

-

-

32

3.3

2.2

0.55

[8]

100

5.3

2.0

0.47

8

320*

-

-

-

-

1000

4.7

2.0

0.45

12

3,5-dichlorophenol

3.2

6.1

2.6

0.39

24

10

6.3

4.2

0.21

59

3.2

8.1

7.3

0.08

84

* It was not possible to calculate oxygen consumption rates due to very low initial and final oxygen readings

[Increase in respiration rate compared to the control]

Executive summary:

In a 3 -hour toxicity study, activated sludge was inocculated with Cashew Nutshell Extract, Decarboxylated, Distilled (Distilled Grade) at nominal concentrations of 0, 10, 32, 100, 320 and 1000 mg/l. No signs of toxicity were noted at any concentration. This toxicity study is classified as acceptable and satisfies the guideline requirement for a microorganism toxicity study. A similar conclusion is predicted for Cashew (Anacardium occidentale) Nutshell Extract, Decarboxylated (Technical Grade).

Description of key information

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

For the toxicity to sewage treatment works microorganisms endpoint no test data is available for the registered substance, Technical Grade. However data is available for the compositionally similar substance Distilled Grade which is part of the category of the three grades of CNSL. In a 3-hour toxicity study, activated sludge was inoculated with Distilled Grade at nominal concentrations of 0, 10, 32, 100, 320 and 1000 mg/l. No signs of toxicity were noted at any concentration. The available data for the three grades indicates that they all show low measured water solubility in the range 0.2 to 0.3 mg/l. All three substances also show high measured octanol-water partition coefficients (log Kow >6.2 in all cases). This data indicates that the measured data for the key physico-chemical properties that underpin the likely short term aquatic toxicity of the three grades are consistent. On this basis it would be expected that the three grades would show similar responses in the short-term aquatic toxicity tests. This hypothesis is currently supported by the results of the results of the long-term OECD TG218 ecotoxicity test that was conducted on both Distilled Grade and Distillation Residue grades following the interpolation approach. Therefore, it is considered appropriate to read-across from the data for Distilled Grade to Technical Grade with the result that it has been estimated that there will also be no adverse toxicological effects of Technical Grade on sewage treatment works microorganisms.

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