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Short-term toxicity to fish

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Description of key information

For seven category members reliable studies (reliability category 1 or 2) are available with LC50 (96 h) values between 1.13 mg/L (C10 DMA; RL 1) and 0.18 mg/L (C18 DMA; RL 2). With the exception of C16-18 DMA (96h-LC50: 0.82 mg/L; RL1), with increasing chain length decreasing LC50 values are observed

Key value for chemical safety assessment

LC50 for freshwater fish:
0.26 mg/L

Additional information

Dimethyl Alkyl Amines (DMA), which are cationic surfactants at pH relevant in the environment, exhibit strongsorption to test organisms and walls of test vessels due to a combination of ionic and hydrophobic interaction. The sorption coefficient was found to be concentration dependent. Due to these properties the test items are difficult to test in synthetic water and results from such tests depend on the test settings applied.In river water,which contains particulate as well as dissolved organic carbon,Dimethyl Alkyl Amines (DMA) are either dissolved in water or adsorbed to dissolved and particulate matter. Thisreduces the difficulties encountered in tests with synthetic water caused by the high adsorption potential (adsorption losses due to settling on surfaces). In general, the adsorbed fraction of DMA is difficult to extract from the test system, which normally leads to low analytical recoveries especially in the old media, while initially measured concentrations (fresh media) are generally within +/- 20% as recommended by the guidelines. Due to the short exposure periods applied in these tests (semi-static design) these low recoveries cannot be explained by biodegradation.No or negligible sorption to glass ware occurs under these conditions which was confirmed by measurements. This ensures reliable as well as reproducible results andmeans that the test substance is present in the test system and therefore available for exposure (dissolved in water and adsorbed, also called bulk). This so called Bulk Approach is described by ECETOC (2003).Consequently, nominal concentrations were used for these tests instead of measured ones.

Therefore, reliable (reliability category 1) tests with river water as dilution water were newly performed (NOACK, 2012) for four category members with different chain lengths (C10 DMA, C12-14 DMA, C16 DMA and C16-18 DMA). These tests were of semi-static test design (renewal after 48 hours) and involved analytical determination of test item adsorbed to glass walls as well as initial and final test item concentration in test water and are regarded to be of higher reliability and relevance than the tests performed with synthetic dilution water.Natural river water from river “Innerste” (Lower Saxony) was used as dilution water in these tests. This river has been chosen due to its properties representing typical conditions of a German medium sized river. The concentration of suspended matter measured in the river water was in a range of 14.0 to 15.6 mg/L, the non-purgable organic carbon concentration was between 3.2 and 3.3 mg/L.

Sometimes mitigating effects are observed for river water tests compared to tests involving synthetic water. This was not the case for results on acute fish toxicity of DMA. Where reliable studies for both test types are available for comparison (C10, C12-14, C16) results are very close to one another and the LC50 (96 h) value for C10 DMA observed in the river water test was even lower than the one observed with synthetic water (1.13 mg/L and 1.8 mg/L, respectively).

Tested fish species were Zebra fish (Danio rerio, all river water tests and some of the tests performed with synthetic dilution water) and Rainbow trout (Oncorhynchus mykiss).

Determined LC50 (96 h) values are between 1.13 mg/L (C10 DMA; river water test) and 0.18 mg/L (C18 DMA; synthetic test water). The lowest LC50 (96 h) determined using natural river water was 0.26 mg/L for C16 DMA. In comparison, the river water test performed with C16-18 DMA resulted in a 96h-LC50 of 0.82 mg/L (RL 1), pointing to a reduced toxicity of DMA with chain lengths above C16. This result is however in disagreement with the LC50 (96 h) of 0.18 mg/L determined for C18 DMA using synthetic dilution water (RL 2). Further non-reliable studies (RL 3) are available for C12, C16 and C18 DMA with similar LC50 values.

Concluding from this broad data base of reliable acute toxicity tests on fresh water fish, DMA are to be regarded as acutely toxic to freshwater fish. Toxicity seems to increase with increasing chain length up to C16 DMA. For higher chain lengths results are less clear.