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Short-term toxicity to aquatic invertebrates

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Description of key information

Freshwater compartment: 
EC50(48h): 12.5 mg/L (Daphnia magna, OECD 202)
Marine compartment:
EC50(48h): 18.3 mg/L (Americamysis bahia, OECD 202)
Significant mortality: 0 - < 508.3 mg/L (Palaemonetes pugio, EPA-660/3-75-009)
Brackish water:
LC50(96h): 11.8 mg/L (Nitocra spinipes)

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
12.5 mg/L
EC50/LC50 for marine water invertebrates:
18.3 mg/L

Additional information

Taken into account the read-across possibility of m-tolyidene to 2,4,6-triisopropyl-m-phenylene diisocyanate, which is scientifically justified (please refer to the read-across statement), experimental data are available for freshwater, marine and brackish water invertebrates.

For the freshwater compartment, Daphnia magna was used as test organisms to investigate the acute toxicity of m-tolylidene diisocyanate according to OECD Guideline 202 (Tadokoro et al., 1997). The main test was conducted with an initial pH of 7.5 and dissolved oxygen of 8.4 - 8.6 mg/L. The test duration was 48 hours, resulting in an EC50 value of 12.5 mg/L. A final total TDA concentration of 5 mg/L was measured, which was expected before, due to the hydrolytic behaviour of TDI. Furthermore, the test was carried out at initial pH values of 6 and 9, resulting in EC50 values of 1.6 mg/L and 17.7 mg/L, respectively.

In the second experiment using Daphnia magna according to OECD Guideline 202, three series of tests were performed, 2 of them by dispersing TDI into test medium (reconstituted dilution water) by high speed shearing (20 seconds) and one by magnetic stirrer (30 minutes) prior to use (Caspers et al., 1986). The temperature was adjusted to 20 +/- 1 °C and the test duration was 24 h. Utilizing a magnetic stirrer, it was not possible to determine the EC50 value, due to the fact that the EC100 was higher than 1000 mg/L, but was estimated to be 750 mg/L. From the tests by high speed sharing, an EC50 in the order of 1 - 2 mg/L can be estimated. The high speed shearing condition is not relevant to environmental conditions. Precipitation of insoluble solid test material was observed, resulting from the hydrolytic potential of the test substance. It is predicted, that a significant proportion of the test substance (ca. 35 %) would have been degraded at the start of the toxicity test and degradation would be virtually complete within several hours.

The acute toxicity of m-tolylidene diisocyanate to the marine invertebrate Americamysis bahia was investigated according to OECD Guideline 202 (Tadokoro et al., 1997). The test duration was 48 hours, with a photoperiod of 14 hours. The organisms were fed daily and the pH was adjusted to 7.07 - 7.93. Test material was stirred into a mixture of sea water and well water for 24 hours prior to the experiment. Due to the hydrolytic behaviour of TDI, the substance would have been predominantly hydrolysed during this experiment. The medium contained about 6 mg/L TDA (mixture 2,4- and 2,6-isomers) at the concentration measured of the EC50 value. The EC50 value was determined as 18.3 mg/L.

Curtis et al. (1979) investigated the acute toxicity to the saltwater invertebrate Palaemonetes pugio under static test conditions. The test was performed in accordance to the Committee on Methods for Toxicity Tests with Aquatic Organisms (1975) Methods for Acute Toxicity Tests with Fish, Macroinvertebrates, and Amphibians. U.S. EPA. Ecological Research Series EPA-660/3-75-009. The test duration was 96 h at a temperature of 22 +/- 1 °C without aeration and feeding during the test period. A series of substances were tested, whereby the substances were administered either directly or in the form of stock solutions in deionized water or acetone. The solutions were briefly stirred with a glass rod, then a water sample was withdrawn from one tank at each concentration for quantitative toxicant analysis. The test concentrations were arranged in geometric series with at least a 60 % dilution factor. No significant mortality was observed until a test concentration of 508.3 mg/L ( = LC0). Other effects on test animals were not reported.

Bengtsson (1983) investigated the toxicity of 43 chemicals against the brackish water harpacticoid Nitocra spinipes under static conditions. At least six concentrations per substance and with one control were used and 2 x 10 N. spinipes were exposed to each concentration. The test animals were not fed during the test period. No control analyses for the actual substance(s) were made of the test solutions and no attempt was made to adjust pH. Substances with low solubility in water were first dissolved in acetone (p.a. quality) and then added to the test vessels. The concentration of acetone never exceeded 500 µL/L. The read-across substance was found to have a LC50(96h) of 11.8 mg/L with a 95 % confidence limit of 10.5 - 13.2 mg/L.