Dichloroacetic acid

Short-term toxicity to fish

Description of key information

fish LC50 > 2000 mg/L

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

2 000 mg/L

Marine water fish

Marine water fish

Effect concentration:

321.6 mg/L

Additional information

There are two studies available for this endpoint: one Klimisch 2 study and a disregarded Klimisch 4 study.

In the publication from McHugh Law et al (1998) the effect of DCA on medaka was investigated for a 21 day exposure period using concentrations of 0 (control), 0.5 and 2.0 g/L. The focus of this study was on histopathology. The test design was similar to the design laid out in OECD 204. The test was performed as semi-static test with 20 - 30 % water renewal twice a week. At start of the exposure, the fish had a total length of 7 to 13 mm.

Each test group received 20 fish. The fish were exposed in 40 L aquaria. The test was performed at 27 +/- 1°C. Prior to use, the pH of the stock solution was adjusted to pH 7.0 +/- 0.5. DCA concentrations were verified by measuring absorbance at 250 nm. The fish were fed twice a day.

No mortality was reported for any of the test groups. Based on the table provided, no mortality occurred during the exposure. No remarkable macroscopic abnormalities were found in any of the specimens. Histopathological examination of fish exposed for 21 days to DCA showed that cytoplasmicvacuolation, cell swelling and sinusoidal compression was apparently caused by DCA exposure. This effect was observed at 0.5 and 2.0 g/L. The fish exposed to the lower concentration of DCA had slightly less severe hepatocellular vacuolation and necrosis after 3 weeks of DCA exposure. Fish exposed to DCA for 3 weeks at a concentration of 0.5 g/L had moderate hepatocytomegaly, sinusoidal compression and marked cytoplasmic vacuolation. Vacuoles were demonstrated to contain glycogen by the PAS reaction.

It can be concluded that DCA does not cause mortality of macroscopic changes in juvenile medaka when exposed for 21 days with up to 2 g/L. Histopathological changes in the liver were already observed at the lowest concentration of 0.5 mg/L and effects were seen already after 72 hours of exposure. At 2.0 g/L, the effects were more pronounced than at 0.5 g/L.

Since histopathological investigation is beyond the scope of the test guideline, the evaluation for regular purposes was focused on mortality and macroscopic findings. The LC0 and EC0, i.e., the concentration at which no mortality or macroscopic findings were observed was the highest test concentration investigated, i.e. 2.0 g/L.

Even if the test has not followed the test guideline 204 in all aspects and was not performed under GLP, it is considered that the results of this study can be used for the risk assessment of DCA. The use of smaller size of the fish is expected to be more conservative than using the recommended longer fish. The temperature deviation is considered to have a relevant impact on the outcome of the test.

The LC0 is 2.0 g/L (=2000 mg/L). No adverse macroscopic effects were observed at any concentration until day 21, the end of the exposure.

Since this test was not performed according to OECD 210, 212 or 215 an no growth parameters were measured or reported. Therefore, this test will not be used for the derivation of the long-term EC10. Nevertheless, this test provides evidence that a concentration of 2000 mg/L will cause no mortality in medaka when exposed for 21 days. Based on this study it can be concluded that the EC50 in short term-fish tests is also > 2000 mg/L This concentration will be used for the risk assessment for freshwater fish. 

In the publication from Fisher et al (2014) the toxicity of DCA on sheepshead minnow (Cyprinodon variegatus ) was investigated in brackish water. The test was performed according to USEPA manual for determining the acute toxicity of effluents and receiving waters to freshwater and marine organisms (USEPA, 2002). The pH was not adjusted. In total 5 concentrations were tested in this semistatic test (renewal at 48 hours). The test was performed for 96 hours. Chemical stability tests indicate that dichloroacetic acid is stable. There is a strong relationship between dichloroacetic acid, pH, and C. variegatus acute test mortality. Measured test concentrations of 754.0 and 377.0 mg/l dichloroacetic acid had pH values below 3.00 and caused complete mortality within 24 h. The 96-h LC50 value was 321.6 mg/l. Mortality at the highest dichloroacetic acid concentrations was extremely rapid, resulting in 24-h, 48-h, and 72-h LC50 values of 321.6 mg/l, the same as the 96-h LC50.

In this test very young fish were used. Typically, smaller fish are more sensitive than older fish as they are recommended in the OECD guideline. Furthermore, the pH was not adjusted and it was speculated that the decreased pH caused the mortality. Therefore, the LC50 of 321.6 mg/L is considered to be very conservative.

The LC50 is considered relevant and reliable for the risk assessment for marine fish.

The Klimisch 4 study confirms that the LC0 is > 100 mg/L. However, due to technical shortcommings, that study can not be used for teh risk assessment.