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Long-term toxicity to aquatic invertebrates

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Description of key information

The key study evaluated the effect of the water-accommodated fraction (WAF) of the test substance on reproduction and growth of the daphnid, Daphnia magna Straus, in a 21-day semi-static renewal limit test (OECD 211 test guidelines).

The test substance mean WAF loading rate was 146 mg/L. A Control treatment consisting of dilution water with no test substance was also prepared. The WAF was prepared by adding the appropriate amount of test substance to dilution water in a glass aspirator bottle and stirring on a magnetic stirplate for approximately 24 hours. The mixtures were allowed to settle for 1 hour (± 15 minutes) before removing the aqueous portion (WAF) for testing. The WAF was removed through an outlet at the bottom of the mixing vessel. The WAF and Control treatments were renewed at 48-hour intervals using a WAF that was prepared 24 hours prior to renewal.

Based on this limit test following OECD 211 test guidelines, the test substance did not cause any chronic adverse effects to Daphnia magna reproduction or survival at its water solubility limit. Therefore the 21-day chronic No Observed Effect Loading Rate (NOELR) for the test substance was determined to be >146 mg/L for both organism length and reproduction. This endpoint is based on the mean actual loading rate of test substance to the dilution medium. To verify concentration stability of the WAF solution, analytical monitoring was conducted (TOC measurements). However, it was not possible to verify the concentration stability of the test substance in the WAF solution, due to the extremely low aqueous solubility of the test substance. The aqueous solubility of the test substance is approximately 2.4E-5 mg/L based on a QSAR estimates, further confirmed by aqueous solubility measurement data which indicate that the aqueous solubility is below an analytical limit of determination of <0.001 mg/L. Therefore, concentration stability in the WAF solution was ensured by way of a high loading rate (146 mg/L), long WAF equilibration times (24 hr), and the regular WAF renewals (every 48 hr) throughout the duration of the test. The findings indicate that the test substance did not cause any chronic adverse effects to Daphnia magna reproduction and survival at its water solubility limit under the conditions of the OECD 211 test.

Key value for chemical safety assessment

Additional information

The findings of the key study are further supported by long-term toxicity data for a structurally related alkylnaphthalene, MCP 2395 (eicosanylnaphthalene analog) for read-across assessment.  The chronic toxicity of MCP 2395 as measured by the reproductive capacity of Daphnia magna was evaluated in freshwater for MCP 2395. Relative to controls, the test material did not cause adverse effects to survival/mobilization nor to reproduction of Daphnia magna under the WAF conditions of the 21-day limit test, which was conducted at the water solubility limit of MCP 2395. The 21-day No Observed Effect Loading Rate (NOELR) of MCP 2395 was >103 mg/L WAF for both reproduction and growth.

Hence, based on the read-across data for the structurally related alkylated naphthalene surrogate, the submission substance (naphthalene, reaction products with tetradecene) is not expected to cause chronic toxicity to invertebrates at its water solubility limit as evaluated with WAF conditions.