1,1'-dithiobis[hexahydro-2H-azepin-2-one]

Short-term toxicity to fish

Description of key information

LC50(96h): 7.5 mg/L 
NOEC(96h): 5.6 mg/L 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

7.5 mg/L

Additional information

The acute toxicity to fish of the test substance was investigated according to OECD Guideline 203 and EU Method C.1 in two different experiments (key and supporting information, Klimisch 1 and 2, respectively).

In the key study, a semi-static freshwater test, rainbow trout (Oncorhynchus mykiss) was used as test organisms (Wetton and Mullee, 2001). This species are freshwater fish representatives of a wide variety of natural habitats, and can therefore be considered as an important non-target organism in freshwater ecosystems. The study was conducted under certificated GLP compliance. The test concentration to be used in the definitive test was determined by a preliminary range-finding test. Based on this range-finding study, the substance was tested in concentrations of 1.0, 1.8, 3.2, 5.6 and 10.0 mg/L, whereby the test material was dissolved directly in dechlorinated tap water. The acclimatisation period of the juvenile fish was conducted for 13 days. The stock fish were fed commercial trout pellets which was discontinued 24 h prior to the start of the definitive test. There was no mortality in the 7 days prior to the start of the test and the fish had a mean standard length of 4.5 cm (sd = 0.3) and a mean weight of 1.12 g (sd = 0.22) at the end of the definitive test. At the start of the test 10 fish were placed in each test vessel at random, giving a loading rate of 0.51 g bodyweight/L. The experiment was performed at 14.0 °C in a temperature controlled room with a photoperiod of 16 h light and 8 h darkness with 20 min dawn and dusk transition periods for a period of 96 h. The test vessel lids were completely sealed and received no auxiliary aeration. A semi-static test regime was employed involving a daily renewal of the test preparations to ensure that the concentrations of the test material remained near nominal and to prevent the build up of nitrogenous waste products. The water temperature, pH and dissolved oxygen concentrations were recorded daily throughout the test. All sample preparations were observed to be clear, colourless solutions throughout the test. The control group was maintained under identical test conditions but not exposed to the test material. No abnormalities as well as no dead fish were detected in this group. The same results were reported for the test concentrations of 1.0, 1.8, 3.2 and 5.6 mg/L. The only sub-lethal effect of exposure (swimming at the bottom of the test vessels) was observed at the test concentration of 10 mg/L after 48 h exposure period. At the time point of 72 h all fish were dead. The LC50 was determined as 7.5 mg/L with 95 % confidence limits of 5.6 - 10.0 mg/L. The No Observed Effect Concentration (NOEC) was 5.6 mg/L.

In a supporting study, zebrafish (Danio rerio) were chosen as test organisms (Rudolf, 2004). The experiment was conducted for 96 h at a temperature of 23 +/- 1°C. Two main studies were conducted after a pre-test. The pre-test was conducted after a 14 d acclimatisation period with test material concentrations of 0, 10, 100 and 1000 mg/L, whereby 100 % mortality was recorded at concentrations of 100 and 1000 mg/L. A fish is considered as dead when no own movement can be observed after touching the caudal peduncle of the animal. For reasons of animal welfare, the pre-test was performed with three fish per treatment. Based on this range-finding study, the substance was tested in concentrations of 0, 10, 32, 56 and 100 mg/L, whereby the test material was dissolved directly in dechlorinated tap water. 100 % mortality was again recorded at concentrations of 56 and 100 mg/L. After 96 h 71 % mortality was observed at a concentration of 32 mg/L. Due to this observation a second main study was conducted with 0 and 18 mg/L test substance concentration, whereby no mortality was recorded in this case. Seven fish per treatment were used in the main studies. The 96 h results were as followed: LC50: 31 mg/L, LC100: 56 mg/L and the No Observed Effect Loading rate (NOEL) is 18 mg/L.