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Long-term toxicity to aquatic invertebrates

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Description of key information

For two category members reliable studies (reliability category 1) are available resulting in NOEC values (21 d, reproduction) between 36 µg/L (C12-14 DMA) and 100 µg/L (C16-18 DMA).  

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
36 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 (without restrictions, reliability category 1) tests with river water as dilution water were performed for two category members with different chain length (C12-14 DMA and C16-18 DMA). These tests were of semi-static test design (daily renewal for C16-18 DMA and 3 times/week for C12-14 DMA) and involved analytical determination of test item in the stock solution, adsorbed to glass walls (C16-18 DMA only) as well as initial and final test item concentration in test water and are regarded to be of higher reliability and relevance than tests performed with synthetic dilution water would be.Natural river water from river “Innerste” (Lower Saxony; C16-18 DMA) and “Boehme” (Lower Saxony; C12-14 DMA) was used as dilution water in these tests. These rivers had been chosen due to their properties representing typical conditions of German medium sized rivers. The concentrations of suspended matter measured in the river waters was 14.0 and 19 mg/L, respectively and the organic carbon concentration was 3.2 mg/L (NPOC, Innerste) and 6.6 mg/L (DOC, Boehme). Both tests were performed according to OECD 211, compliant to GLP and fulfilling validity criteria of the guideline.

ForC16-18 DMAtheNOEC (21 d) for reproduction and adult mortality was 100 µg/LEC10- or EC50 values for the reduction of the reproductive output could not be estimated, because no reduction of the reproductive output > 10 % was observed within the tested concentration levels with surviving daphnids of 12.5 to 100 µg/L. At the next higher concentration (200 µg/L) there were no surviving adults, i.e. the endpoint reproduction wasn´t any more sensitive than the endpoint adult mortality. Comparing the calculated chronic EC50 (21 d) for adult mortality of 141 µg/L with the determined acute toxicity of C16-18 DMA (48-h EC50: 190 µg/L; river water test) shows no significant higher sensitivity upon chronic exposure. This may point to toxicity due to adsorption of the test item to the surface of daphnids, i.e. physicochemical mechanism of toxicity.

Due to 13 stillborn juveniles found at 108 µg/LC12-14 DMAbut n≤1 for all other tested concentrations of the test item, this effect was determined to be statistically significant in spite of a reproductive output of 760 living juveniles (n= 10 parental daphnids) at this concentration, corresponding to a statistically not significant reduction of the reproductive output by 4% compared to the control. At the next higher concentration (320 µg/L) only 3 parental daphnids survived (21-d EC50 immobilization: 280 µg/L) and the EC50 (21 d) for reproductive output was determined as 310 µg/L. In comparison, the 48-hour EC50 for immobilisation is lower than the chronic one. This uncommon finding is probably due to the higher concentrations of DOC (6.6 mg/L) and suspended matter (19 mg/L) of “Boehme” water compared to water from “Innerste” used in the acute daphnia test. Thus, in principal the same may hold true for C12-14 like what was stated above for C16-18 DMA, i.e. reproduction being not any more sensitive than survival and toxicity being probably due to physicochemical interaction (adsorption). However, due to the statistically significant number of stillborn juveniles found at 108 µg/L theNOEC (21 d, reproduction) was set at 36 µg/L.

In conclusion, members of the DMA category are to be regarded as chronically toxic to aquatic invertebrates. However, chronic toxicity seems not to be pronouncedly higher than acute toxicity exerted by DMA and compared to immobilization the reproductive endpoint is of similar sensitivity.