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Toxicity to aquatic algae and cyanobacteria

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Description of key information

A number of studies investigated the toxicity of chloroform to freshwater algae. Valid studies are available for freshwater green and blue-green algae only (Bringmann and Kühn 1975-1980, Kühn and Pattard 1990, Brack and Rottler 1994). Only the latter study applied analytical methods to monitor the concentrations of chloroform in the test solutions. Information about the toxicity of chloroform to marine species is available from studies which are considered as not reliable. The most reliable study established a NOEC value of 3.61 mg/L for inhibition of growth in green algae. This value is considered in the risk assessment.

Key value for chemical safety assessment

EC50 for freshwater algae:
13.3 mg/L
EC10 or NOEC for freshwater algae:
3.61 mg/L

Additional information

The various tests carried out by Bringmann and Kühn between 1975 and 1980 on freshwater green algae (Scenedesmus quadricauda) and blue-green algae (Microcystis aeruginosa) and by Kühn and Pattard (1990) on Scenedesmus subspicatus did not apply analytical methods to verify the chloroform concentrations of the test solutions. However, the test vessels were closed so that loss of the test substance over the period of the tests (7 to 8 days) was likely to be reduced. The NOEC values or EC10 values of these tests are in the range of 185 to 1100 mg/L.

The only test on algae with analytical monitoring of the chloroform concentrations in the test solutions by GC/ECD analysis was the study by Brack and Rottler (1994) on the freshwater green algae Chlamydomonas reinhardii. They used a closed system of bipartite culture flasks which avoided significant losses of chloroform during the test. CO2 was supplied by a KHCO3/K2CO3 buffer. Inhibition was only measured related to biomass for each concentration and not related to algal growth rate, which is usually the preferred observational endpoint. The EC10 value (72 hours) determined in the test was 3.61 mg/L. This value is considered to be reliable because the validity criteria of the test were fulfilled, the study was the only one with analytical monitoring and the NOEC was the lowest of all experimental values.

The tests on marine diatoms (Skeletonema costatum and Thalassiosira pseudonana) provided results that are considered to be not reliable (Cowgill et al. 1989, Erickson and Freeman 1977). The NOEC values (5 to 7 days) of these studies tend to be considerably higher than the one of Brack and Rottler (1994).

Thus, the EC10 value of 3.61 mg/L for the toxicity of chloroform to algae and cyanobacteria is used in the risk assessment and is considered to represent both, freshwater and marine species.