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Short-term toxicity to aquatic invertebrates

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Description of key information

For four category members six reliable studies (reliability category 1 or 2) are available with EC50 (48 h) values between 930 µg/L (C10 DMA; RL 1) and 56 µg/L (C12-14 DMA; RL 1). No obvious relationship between chain length and toxicity exists. 

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
56 µg/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 24 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 invertebrate toxicity of DMA. Where reliable studies for both test types are available for comparison (C10, C12-14) results are very close to one another and EC50 (48 h) observed in the river water test was even lower than the one involving synthetic water for C12-14 DMA (56 µg/L and 83 µg/L, respectively).

Determined EC50 (48 h, immobility) is highest for C10 DMA (930 µg/L; river water; RL 1), intermediate for C16-18 DMA (190 µg/L; river water; RL 1) and lowest for C12-14 and C16 DMA (56 µg/L and 67 µg/L, respectively; river water; RL 1). Thus judging from reliable experimental test results, while there is no evident relationship between chain length and toxicity, members of the DMA category are to be regarded as acutely toxic to aquatic invertebrates