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Toxicity to terrestrial plants

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Description of key information

NOEC 0.0237 g/ha, EC50 0.0907 g/ha, EC25 0.0237 g/ha, EPA OPPTS 850.4225 and 850.4250, Schwab 2000.

Key value for chemical safety assessment

Additional information

Schwab (2000) is a tier 2 toxicity study performed on ten different crop species; Daucus carota, Cucumis sativus, Lactuca sativa, Raphanus sativus, Glycine max, Lycipersicon esculentum, Zea mays, Lolium perenne, Avena sativa and Allium cepa. Plants were all exposed to the test material in a single application made over a dosing range of 52, 26, 13, 6.5, 3.25, 1.63, 0.815 and 0.408 g/ha. Plants were observed for two to three weeks and assessed for visible injury, percent emergence and growth in the emergence test and visible injury and growth in the vegetative vigour test.

Under the conditions of the test effects on growth were observed in all species with the exception of the tomato in the vegetative vigour test. The species identified as being most sensitive according to the different effect parameters are the radish, lettuce and ryegrass. Overall the most sensitive endpoint appears to be visible injury where the radish was shown to be the most sensitive species according to phytotoxic ratings.

All species rated for visible injury in the emergence test exhibited a significant difference from the controls. The lettuce and radish were considered to be the most sensitive having NOEC values of 0.815 and 0.640 g/ha, respectively. EC₅₀ values for the two species were determined to be 4.66 and 8.87 g/ha. The main effects noted were stunting and chlorosis.

 The radish was also considered the most sensitive in the vigour test based on phytotoxic ratings with corresponding NOEC and EC₅₀ values of 0.0237 and 0.0907 g/ha.

Out of the 10 different plant species tested for percentage emergence five showed significant (p=0.05) difference from the control, where ryegrass was considered to be the most sensitive. The NOEC was determined to be 6.5 g a.i./ha and the EC₅₀ of 15.2 g/ha.

All species showed a significant (p=0.05) difference, in comparison to the control, for both shoot length and shoot weight in the emergence test. Lettuce was the most sensitive plant following a pre-emergence application of the test material. The NOEC and EC₅₀ values were determined to be 0.815 and 5.41 g/ha, respectively, for shoot length. The NOEC and EC₅₀ for shoot weight were determined to be 0.815 and 3.32 g g/ha.

Comparison of plant shoot length and dry weigh to controls showed that again the radish was the most sensitive species in the vegetative vigour test. All species showed significant difference (p=0.05), with the exception of the Tomato, lettuce did not show significance for shoot length alone. The radish shoot length NOEC and EC₅₀ were determined to be 0.0710 and 2.74 g/ha, respectively. The radish dry weight NOEC and EC₅₀ were determined to be 0.0237 and 0.139 g/ha, respectively.

The study was performed according to GLP, in line with standardised guidelines, with a high standard of reporting and has thus been assigned a reliability score of 1 in line with the principles for assessing data quality set out by Klimisch (1997). The study is considered to be reliable, relevant and adequate for risk assessment purposes.

The available data are considered to be complete and the following conclusions for toxicity have been taken forward for risk assessment based on the worst case scenario using the most sensitive data; NOEC 0.0237 g /ha and EC₅₀0.0907 g/ha (all concentrations are representative of the active ingredient and corrected for sample purity).

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