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Toxicity to aquatic plants other than algae

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Description of key information

Freshwater: IC50 = 11 µg a.i./L, NOAEC = 1.6 µg a.i./L, Lemna gibba, EPA 540/9-82-020, Thompson & Swigert 1997b

Key value for chemical safety assessment

Additional information

The toxic effects of the test material to aquatic plant species was determined in a 14-day toxicity study performed on Lemna gibba. The study was conducted according to GLP and in line with the standardised guideline EPA 540/9-82-020. L. gibba were exposed to the test material at initial measured concentrations of 0.40, 0.81, 1.6, 3.2, 6.1, 14 and 26 µg a.i./L under static freshwater conditions. The test solutions were analysed by HPLC, due to a decline in test material concentration over the exposure period, the results were expressed relative to Day 0 concentrations. Each concentration was tested in triplicate with negative and solvent controls run concurrently for comparison. Five plants totalling 15 fronds were used to initiate each replicate. Direct counts of frond numbers were performed on Days 3, 6, 9, 12 and 14. Cultures were also monitored for chlorosis, necrosis, break-up, root destruction, death and any other abnormalities.

 

Under the conditions of the test signs of toxicity were observed at concentrations ≥ 3.2 µg a.i./L. The most sensitive parameters were necrotic and dead fronds, frond size and root destruction, where plants were significantly (p<0.05) affected at concentrations ≥ 3.2 µg a.i./L. Significant (p<0.05) reductions in frond and plant production in comparison to the pooled controls were observed at concentrations ≥ 6.1 and ≥ 26 µg a.i./L, respectively. Break up was first observed on Day 9 of exposure in the 14 µg a.i./L treatment group and by Day 6 in the 26 µg a.i./L group. There was no statistical (p>0.05) difference in chlorotic fronds, in comparison to the pooled controls, at any of the concentrations tested.

Based on these findings the IC50 was determined to be 11 µg a.i./L with 95% confidence limits of 8.7 and 13 µg a.i./L; the NOAEC was determined to be 1.6 µg a.i./L.

The study was performed to a high standard, according to GLP and a standardised guideline. Accordingly the study has 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 deemed to be relevant, reliable and adequate for the purposes of risk assessment.

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