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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Freshwater
120 h EC50 0.27 mg/L, NOAEC 0.20 mg/L EPA OPPTS 850.5400, EPA OPP 123-2, Desjardins et al (2006)
120 h IC50 266 µg/L, NOEC 64.1 µg/L, EPA OPP 122-2 and 123-2, Kranzfelder 2000a
120 h IC50 6.5 µg/L, NOEC 1.13 µg/L, EPA OPP 122-2 and 123-2, Kranzfelder 2000b
120 h IC50 > 150 mg/L, NOEC 150 mg/L, EPA OPP 122-2 and 123-3, Kranzfelder & Malorin (1999a)
Marine water
120 h IC50 80 mg/L, NOEC 37.0 mg/L, EPA OPP 122-2 and 123-3, Kranzfelder & Malorin (1999a)

Key value for chemical safety assessment

EC50 for freshwater algae:
6.5 µg/L
EC50 for marine water algae:
80 mg/L
EC10 or NOEC for freshwater algae:
1.13 µg/L
EC10 or NOEC for marine water algae:
37 mg/L

Additional information

Toxicity to aquatic algal and cyanobacteria has been addressed on a weight of evidence basis, where four studies have been provided to address toxicity in freshwater and one in marine water.

All five studies were performed under static conditions where various test organisms were exposed to the test material over a range of concentrations for 120 hours. Effects on cell density were used to quantify toxicity. HPLC was used to analyse and verify exposure solution concentrations in all studies. Control cultures were shown to grow exponentially with a low coefficient of variation between the replicates, thus confirming the viability of the test system.

Desjardins et al (2006) was performed in freshwater with Anabaena flos-aqua. The test organisms were exposed the test material at measured concentrations of 0.041, 0.087, 0.20, 0.43, 0.97 and 2.2 mg/L. Significant inhibition was observed at concentrations ≥ 0.43 mg/L (p<0.05) and had a clear dose response pattern. No other abnormal effects were noted during observations of the cells. A 5 day post exposure recovery period showed the effects to be algistatic. The 120 hour EC₅₀ was determined to be 0.27 mg/L, with 95 % confidence limits of 0.18 and 0.41 mg/L, and the 120 hour NOAEC was 0.20 mg/L.

Kranzfelder (2000a) was performed in freshwater with Anabaena flos-aqua. The test organisms were exposed the test material at measured concentrations of 0.113, 0.289, 1.05, 5.31, 19.8, 64.1 and 266 µg/L.Significant inhibition was observed at 266 µg/L (p<0.05). Percentage change in cell density relative to the control ranged from -2 % at 0.389 µg/L to -52 % at 266 µg/L .The IC₅₀ was calculated to be 280 µg/L. The cell density data confirmed the IC₅₀ value was approximately 266 µg a.i./L, the highest test concentration. The 120 hour NOEC was determined to be 64.1 µg/L.

Kranzfelder (2000b) was performed in freshwater with Selenastrum capricornutum. The test organisms were exposed the test material at measured concentrations of 1.13, 2.64, 4.54, 8.02, 18.7 µg/L. Significant (p≤ 0.05) inhibition of growth was observed at all concentrations test concentrations, in comparison to the control. However significance at 1.13 µg/L was considered to have been a result of the low coefficient of variation in the control. The percentage inhibition in cell growth ranged from -8 % at 1.13 µg/L to -83% at 18.7 µg/L. The NOEC was determined to be 1.13 µg/L. The IC₅₀ was determined to be 6.5 µg/L with 95 % confidence limits of 5.8 and 7.2 µg/L. The results obtained from this study, being the most sensitive, have been selected to represent the effects of the test material based on the worst case scenario in freshwater.

Kranzfelder & Malorin (1999a) was performed in freshwater with Navicula pelliculosa. The test organisms were exposed the test material at measured concentrations of 8.49, 17.4, 34.7, 69.1, 139 mg/L. No significant growth inhibition was observed at any of the concentrations tested. The percent change in cell growth after exposure ranged from -7 to 5 %. Thus the NOEC was determined to be 150 mg/L and it can be said that the IC₅₀> 150 mg/L.

Kranzfelder & Malorin (1999b) was performed in marine water with Skeletonema costatum. The test organisms were exposed the test material at measured concentrations of 9.02, 18.3, 37.0, 73.5, 144 mg/L. Significant (p≤ 0.05) inhibition of growth was observed at all concentrations ≥ 73.5 mg/L, additionally percentage inhibition in cell growth ranged from 0 to 88 %. No abnormal cell morphologies were noted. The NOEC was determined to be 37.0 mg/L. and the IC₅₀ was determined to be 80 mg/L with 95 % confidence limits of 76 and 85 mg/L. As this is the only available data regarding marine toxicity, the values determined during this study have been selected to represent the effects of the test material.

All five studies were performed according to GLP, in line with standardised guidelines, with a high standard of reporting and have thus been assigned a reliability score of 1 in line with the principles for assessing data quality set out by Klimisch (1997).

The available data are considered to be complete and the following conclusions for short term toxicity have been taken forward for risk assessment: Freshwater NOEC and IC₅₀ of 1.13 and 6.5 µg/L, respectively; marine water NOEC and IC₅₀ of 37.0 and 80 mg/L, respectively.

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