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Long-term toxicity to aquatic invertebrates

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Reference
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Justification for type of information:
Cresols are isomers and, thus ideally fulfill the recommended criteria of structural similarity. In its chemical structure, a cresol molecule has a methyl group substituted onto the benzene ring of a phenol molecule, by different arrangement of the -CH3 groups are three structural isomers possible. (ortho-cresol, meta-cresol and para-cresol). Of particular importance to environmental effects are the values for partition coefficient (log Kow), vapour pressure, water solubility and dissociation constant. The values of the isomers are very close together, resulting in the same environmental fate and behaviour. Further, with regard to the bioderadation behavior, all 3 cresols are readily biodegradable. Concerning aquatic toxicity of the cresols on aquatic species, a large number of experimental results from tests with fish, invertebrates and algae are available, indicating a similar toxicity of all isomers, with p-cresol being slightly more toxic in acute tests: Based on the similarities in the results mentioned above the read-across approach is therefore scientifically justified.

Reason / purpose for cross-reference:
read-across source
Qualifier:
according to guideline
Guideline:
other: Preliminary guideline proposal of the German Umweltbundesamt, state 1984-01-01
Deviations:
no
GLP compliance:
not specified
Analytical monitoring:
yes
Vehicle:
no
Test organisms (species):
Daphnia magna
Details on test organisms:
IRCHA strain - Age: 24 h
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
21 d
Hardness:
16° dH (2.5 mmol/l Ca + Mg)
synthetic fresh water
Test temperature:
25 +/- 1 °C
pH:
8.0 +/- 0.2
pH values were measured during the test in two tests-vessels per concentration level. The detected variation of the parameter had
no negative influence on the organisms.
Dissolved oxygen:
oxygen-concentrations were measured during the test in two tests-vessels per concentration level. The detected variation of the parameter had
no negative influence on the organisms.
Salinity:
Na/K ratio: 10:1
Nominal and measured concentrations:
- Tested concentration range: 0.003-10 mg/L (nominal)
Details on test conditions:
Determination of NOEC for reproduction rate, parent mortality, and
the time of the first appearance of offspring - Number of replicates: 4 - individuals per replicate: 20
Reference substance (positive control):
yes
Remarks:
chromate
Key result
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
1 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
the most sensitve parameter (of parent animal mortality, reporduction rate, and appearance of first offspring) was used for NOEC determination

- Only the nominal value for the most sensitive parameter is given. However, no losses were reported to be greater than 20%.
- Tested concentration range: 0.003-10 mg/L

Validity criteria fulfilled:
not specified
Conclusions:
The long-term toxicity of p-cresol to aquatic invertebrates was determined in a semi-static test according to the preliminary guideline proposal of the German Umweltbundesamt from 1984. After 21 days of exposure a NOEC of 1 mg/l was determined. This toxicity study is classified as acceptable and satisfies the guideline requirements for the chronic invertebrate study.
Executive summary:

The long-term toxicity of p-cresol to aquatic invertebrates was determined by a test according to the preliminary guideline proposal of the German Umweltbundesamt from1984. In a semi-static test with Daphnia magna, each 20 individuals (24 h old) in 4 replicates were exposed to p-cresol in a concentration range of 0.003 - 10 mg/l. The test solutions were renewed 3 times per week, their stability was controlled by analytical monitoring. After 21 days of exposure a NOEC of 1 mg/l was determined.

Description of key information

No data on chronic toxicity towards aquatic invertebrates are available for o-cresol and therefore, a read-across from p-cresol is applied. The long-term toxicity of p-cresol to aquatic invertebrates was determined in a semi-static test according to the preliminary guideline proposal of the German Umweltbundesamt from1984. After 21 days of exposure a NOEC of 1 mg/l was determined.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
1 mg/L

Additional information

There is no study on chronic toxicity towards aquatic invertebrates available using o-cresol as test substance.

In order to get a comprehensive data set for o-cresol a read-across from p-cresol is applied, in accordance with the following justification:

Justification for the read-across approach:

Data from substances who’s physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be used in a read-across approach in order to avoid unnecessary animal testing. It can be stated that the 3 cresols act as a prime example of substances that are suitable for read-across. Cresols are isomers and, thus ideally fulfill the recommended criteria of structural similarity. In its chemical structure, a cresol molecule has a methyl group substituted onto the benzene ring of a phenol molecule, by different arrangement of the -CH3 groups are three structural isomers possible. (ortho-cresol, meta-cresol and para-cresol). Of particular importance to environmental effects are the values for partition coefficient (log Kow), vapour pressure, water solubility and dissociation constant. The values of the isomers are very close together, resulting in the same environmental fate and behaviour. Further, with regard to the bioderadation behavior, all 3 cresols are readily biodegradable. Concerning aquatic toxicity of the cresols on aquatic species, a large number of experimental results from tests with fish, invertebrates and algae are available, indicating a similar toxicity of all isomers, with p-cresol being slightly more toxic in acute tests: Based on the similarities in the results mentioned above the read-across approach is therefore scientifically justified.

The study resulting in the most sensitive NOEC ist used for read-across.

The OECD SIDS document for o-cresol had presented QSAR data for a 21 -day chronic daphnia test with: 21d-NOEC=1 - 1.5 mg/L. Although QSARs for long-term tests should be used for orientation only, it is validated by the outcome of this test (Kuehn 1988, 21d-NOEC=1 mg/L) which is in agreement with the QSAR prediction of 1 - 1.5 mg/L.

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