Decyldimethylamine

Short-term toxicity to fish

Description of key information

For seven category members reliable studies (reliability category 1 or 2) are available with LC50 (96 h) values between 6.09 µM (C10-DMA; RL 1) and 0.605 µM (C18-DMA; RL 2). With the exception of C16-18-DMA (96h-LC50: 2.85 µM; RL1), with increasing chain length decreasing LC50 values are observed.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

LC50

Effect concentration:

0.26 mg/L

Additional information

Dimethyl Alkyl Amines (DMA), which are cationic surfactants at environmentally relevant pH, exhibit strong sorption 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. This reduces 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 glassware occurs under these conditions which was confirmed by measurements. This ensures reliable as well as reproducible results and means 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-DMA) 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 (6.09 µM and 9.71 µM, 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). The following table gives a summary on the available key studies on acute fish toxicity.

 

Table: Summary of available key studies (river water tests given in bold face)

	C10-DMA	C12-DMA	C12-14-DMA	C14-DMA	C16-DMA	C16-18-DMA	C18-DMA
Water type	river water	laboratory water	river water	laboratory water	river water	river water	laboratory water
Vehicle	no	ethanol	no	no	no	no	HCO-40
Species	Danio rerio	Danio rerio	Danio rerio	Danio rerio	Danio rerio	Danio rerio	Oncorhynchus mykiss
LC50 (96 h) [µM]	6.09	3.31	2.81	1.45	0.95	2.85	0.605

Determined LC50 (96 h) values are between 6.09 µM (C10 DMA; river water test) and 0.605 µM (C18-DMA; synthetic test water). The lowest LC50 (96 h) determined using natural river water was 0.950 µM (0.26 mg/L) for C16-DMA. In comparison, the river water test performed with C16-18 DMA resulted in a 96h-LC50 of 2.85 µM (RL 1), pointing to a reduced toxicity of DMA with chain lengths above C16. While this result is in disagreement with the LC50 (96 h) of 0.605 µM determined for C18-DMA using synthetic dilution water (RL 2), generally river water studies are deemed more reliable (higher reproducibility) for DMAs (see explanations above), and the study on C18-DMA used HCO-40 as dispersant, which may have affected the toxicity of C18-DMA. Based on a fraction of ca. 67% of C18-DMA in C16-18-DMA, even if toxicity is solely ascribed to the fraction of C18-DMA (reduction of LC50 by ca. a factor of 1.49), the LC50 derived from the river water study on C16-18-DMA would still result in a LC50 of 1.91 µM. This is considerably above the result on C18-DMA with laboratory water and HCO-40 as dispersant. On the other hand, performing the analogous considerations under the assumption that full toxicity would be attributable to C16-DMA (ca. 32% in C16-18-DMA), this resulted in a reduction of the LC50 by a factor of ca. 3.13, giving an LC50 of 0.912 µM, which is very close to the value actually obtained in the river water study on C16-DMA. This corroborates that C16-DMA may actually be more toxic compared to C18-DMA. Further non-reliable studies (RL 3) are available for C12, C16 and C18 DMA with similar LC50 values.

Concluding, from this broad database of reliable acute toxicity tests on fresh water fish, DMAs 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, but indicate no further increase or even a decrease of toxicity. Based on the highest toxicity observed for C16-DMA in the reliable river water test, this LC50 (96 h; nominal; analytical verification) of 0.950 µM is used as the key value for the category. However, the original value obtained with C16-DMA of 0.26 mg/L C16-DMA is used as key value. This is justified because a) molar concentration cannot be used for environmental hazard and risk assessment and b) correction for MW would theoretically result in somewhat lower values for shorter chain DMAs, but available reliable river water studies demonstrate a much lower toxicity for C12-14- and C10-DMA (see table above).