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Short-term toxicity to aquatic invertebrates

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Description of key information

All valid freshwater tests with Daphnia magna were carried out without analytical verification of the test solution concentrations. LC50 values in these tests were 29 mg/L, 79 mg/L and 79 mg/L respectively. The NOEC values were < 7.8 mg/L and 48 mg/L in two of the tests. The most reliable test was carried out with marine oyster larvae (Crassostrea gigas) (Johnson and Harman 2002). The EC50 value established in the study for abnormal development of the giant Pacific oyster embryos was 152.5 mg/L and the NOEC value established in the most reliable study with oyster exposed to chloroform for 48 hours was 50.4 mg/L. The effect levels of the most reliable study will be considered in the risk assessment.

Key value for chemical safety assessment

Marine water invertebrates

Marine water invertebrates
Effect concentration:
152.5 mg/L

Additional information

Three tests on the short-term toxicity of chloroform to the freshwater species Daphnia magna have been found that used closed, static test systems thus avoiding excessive volatilisation of chloroform during the test period (LeBlanc 1980, Albernethy et al. 1986, Kühn et al. 1989). However, all of these tests were carried out without analytical verification of the test solution concentrations. The tests found LC50 values of 29 mg/L, 79 mg/L and 79 mg/L, respectively.

A test carried out with the marine brine shrimp (Artemia salina) found similar sensitivity of this marine species with 24-hour EC50 values between 31 and 37 mg/L (Foster and Tullis 1985).

A test on the marine giant Pacific oyster (Crassostrea gigas) was chosen as the key study for the characterisation of the short-term toxicity of chloroform to aquatic invertebrates (Johnson and Harman 2002). The study was carried out with oyster embryos according to ASTM Method E724-94. Fertilised ovae were exposed during 48 hours to chloroform. During this period, the embryos were supposed to develop to D-shaped larvae. Under a subsequent microscopic examination, larvae with incompletely developed shells were counted as dead because a retarded development would likely reduce survival. Concentrations were measured at the beginning and at the end of the exposure period. Losses of chloroform during the preparation of the test vessels were < 30 % and losses of chloroform during the 48 hours test period were < 12 %. A clear dose-response relationship could be established and the following endpoints were calculated based on the measured concentrations: 48-h EC50 value = 152.5 mg/L; 48-h LOEC value = 80.4 mg/L, 48-h NOEC value = 50.4 mg/L. The performance of the test system was evaluated by running a simultaneous test using zinc as a reference substance. The 24-h EC50 found in this reference test was 0.4 mg Zn/L which was consistent with historical control data.

These results of the Johnson and Harman (2002) study found much higher effect levels than a previous study on the acute toxicity to larvae of the Eastcoast oyster (Crassostrea virginica) carried out by Stewart et al. (1979). They exposed freshly spawned and fertilised oyster eggs to chloroform in 1.1 L-beakers. In the 100 microgram chloroform/L test system, the initial concentration fell to 14 microgram chloroform/L at the end of the test period of 48 hours. Five tests resulted in a 48-h LC50 value of approximately 1 mg/L deduced from a graph, which is based on initial concentrations. Assuming that the loss of chloroform is the same at the 100 and 1000 microgram/L test series and using the concentrations measured at the 5 and 48 hours timepoints in the 100 microgram/L solution, a time-weighted mean concentration of 385 microgram/L is calculated for the LC50 value, which is by a factor of 400 lower than the value found in the other oyster study (Johnson and Harman 2002).

These differences can be explained to a large extent by methodological short-comings of the Stewart et al. (1979) study, which make their results not reliable. Thus, the results of the study by Johnson and Harman (2002) obtained from a guideline-compliant study will be considered to be most reliable.

The NOEC value for the short-term toxicity to aquatic invertebrates considered in the risk assessment is 50.4 mg/L. This value is considered to be representative of marine and freshwater systems.