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Short-term toxicity to aquatic invertebrates

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Description of key information

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
28 mg/L

Additional information

One study is available for Methyl Salicylate for this endpoint. This study (DION M., 1983) is a screening AFNOR Test on daphnids with a test duration of 24h. Toxicity has been observed and result is reported as nominal concentration as no analytical monitoring as been performed during the test. Based on the uncertainties of the stability of the test item during the test and the duration of exposure of 24hours instead of 48hours as required by OECD Testing Guideline, this study is considered as not reliable.

Therefore, similarly to the assessment of acute toxicity to fish, a weight of evidence approach with results obtained on analog substances is applied for the assessment of the toxicity to aquatic invertebrates of methyl salicylate. Ethyl salicylate (CAS RN 118-61-6) and salicylic acid (CAS RN 69-72-7) are used as analog substances.

 

One reliable key study is available for Ethyl salicylate for this endpoint. In this acute toxicity study (NOACK M., 2001), the acute immobilization (EC50) of the test item Ethyl salicylate to daphnia (STRAUS) was determined according to the method C.2 of the European Directive 92/69/EC and the OECD Guideline 202. The study was conducted under static conditions over a duration of 48 hours. 20 test organisms were exposed to each test concentration and control. The test item dilutions were clearly dissolved after filtration of the saturated solution in all tested concentration levels throughout exposure. The real test concentrations were calculated based on DOC-analysis: 9.2, 19, 40, 84 and 165 mg/L. The 48h-EC50 values were calculated by probit analysis in the tested concentration range. Exposure of daphnids to Ethyl salicylate resulted in a 48h-EC50 value of 28 mg/L (95% confidence interval = 27 to 29 mg/L). Based on the results of this study, Ethyl salicylate is considered asharmful to theaquatic organisms tested in accordance with the Directive 67/548/EC.

It is proposed to use this data for the assessment of the toxicity to aquatic invertebrates of methyl salicylate as a read-across approach. The main assumption to justify the read-across approach is that both substances have a similar chemical structure. Both substances are 2-hydroxybenzoate, one being a methyl ester (i.e. methyl salicylate) and the second one being an ethyl ester (i.e. ethyl salicylate). Therefore, both substances have the same functional groups in their chemical structure, and the addition of an alkyl "CH2" in the ester function for ethyl salicylate compared to methyl salicylate is not expected to have a significant impact on the biological and physico-chemical properties of the substance.

 

This assumption is supported by the physico-chemical information which shows that both substances have very similar physicochemical properties (including water solubility and vapour pressure). The logKow value of ethyl salicylate is slightly higher than the one of methyl salicylate (i.e. 3.09 and 2.55 respectively). It can therefore be expected that ethyl salicylate has higher effect on the biological cells than methyl salicylate, and therefore applying the read-across approach would be a worst case and protective strategy. Even if not completely comparable due to different test conditions, the toxicity data to fish of both substances show that Ethyl Salicylate is more toxic than Methyl Salicylate (i.e. 96hLC50 = 19.7 mg/L for Ethyl Salicylate and 96hLC50 > 100 mg/L for Methyl Salicylate).

 

To support the fact that methyl salicylate is expected to be less toxic than ethyl salicylate, data on salicylic acid is used to show that the 2–hydroxybenzoic acid is less toxic than the methyl ester, and therefore that the lower the 2-hydroxubenzoic form is substituted, the lower is the toxicity. The read-across approach is supported by the physico-chemical information which shows that both substances have very similar physicochemical properties (including logKow). But it should be noted that salicylic acid is more soluble in water than methyl salicylate (i.e. 1.5 - 2.6 g/L at 20°C - 25°C and 625 mg/L and 30°C respectively) and less volatile (i.e. 0.0208 Pa at 25°C and 13 Pa at 20°C respectively), but these differences are not expected to impact the results of the aquatic toxicity test at the concentrations tested.

 

A 48 hours acute toxicity study of salicylic acid toDaphnia magnais available. This study was conducted under static conditions with nominal concentrations from 276 to 2210 mg/L (pH adjusted to 7.45 +/- 0.05). The 48 hours EC50was determined to be 870 mg/L. Based on the results of this study, 2-hydroxybenzoic acid was not classified as harmful toDaphnia magnain accordance with the EC classification criteria.  

 

In conclusion, the result obtained with ethyl salicylate is used in a worst case read-across approach to assess the toxicity to aquatic invertebrates of methyl salicylate.