2-Pyridinesulfonamide, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-, sodium salt (1:1)

Toxicity to aquatic plants other than algae

Description of key information

14 day IC50 (frond number) 0.55 μg/L (95 % CL 0.45 - 0.62 μg/L), 14 Day NOAEC 0.089 μg/L , EPA OPPTS 850 4400, Palmer et al 2001
14 Day EC50 (frond number) 54 ng/L, 14 day NOAEC 28 ng/L, EPA OPPTS 850.4400, OECD 221, Desjardins et al 2006

Key value for chemical safety assessment

EC10 or NOEC for freshwater plants:

49.9 ng/L

Additional information

The toxicity to fresh water aquatic plants has been determined in two key freshwater studies; three studies were available as supporting information.

The first four studies were all performed using Lemna gibba as the test organism, in 14 day static-renewal toxicity studies. All studies were performed according to GLP and followed similar test protocols.

Sutherland et al (2000) used nominal test concentration of the test material at 0.01, 0.1, 1.0 and 10 μg/L, with a concurrently run negative control. Concentrations were verified to be within 108 and 257% of the nominal concentration. The highest recovery was considered to be caused by interference, thus results were interpreted based on nominal concentrations. Under the conditions of the test, adverse effects on frond growth were seen in test groups exposed to 1.0 and 10 μg/L throughout the study. Adverse effects seen in these two groups include reduction in frond number, plant number and plant conditions. The 7 day IC50 was determined to be 0.31μg/L with 95 % confidence limits of -0.32 and 0.74 μg/L. The 14 day IC50 was determined to be 0.52 μg/L with 95% confidence limits of 0.23 and 0.65 μg/L. The lower 7 day IC50 value and wider confidence limits were considered to be due to variability in response in the lower treatment groups and not treatment related. Based on inhibition of growth in the 1.0 and 10 μg/L treatment groups, the Day 14 NOAEC was determined to be 0.1 μg/L.

Palmer et al (2001) exposed plants to measured concentrations of the test material at 0.00092, 0.0097, 0.089, 0.99 and 9.6 μg/L. A preliminary stability study identified the need to revise the test protocol to include renewal of the test solution. Test concentrations were verified by LSC and HPLC, where mean measured concentrations represented between 89.0 and 99.0 % of the nominal concentrations. Under the conditions of the test, the test material caused significant growth inhibition and reduction in frond number at concentrations ≥0.99 µg/L. Increased incidence of chlorotic and necrotic fronds were observed in plants treated at the highest concentration 9.6 µg/L, with other effects such as root destruction, frond curl, small fronds and colony breakup seen in treatment groups 0.99 and 9.6 µg/L. Plants in the negative control appeared healthy and exhibited normal growth throughout the test. The 7 day IC50 was determined to be 0.50 μg/L with 95 % confidence limits of 0.094 and 0.70 μg/L. The 14 day IC50 was determined to be 0.55 μg ai/L with 95 % confidence limits of 0.45 and 0.62 μg/L. The Day 14 NOAEC was determined to be 0.089 μg/L based on the statistically significant (p<0.05) inhibition of growth in the 0.99 and 9.6 µg/L treatment groups.

Kranzfelder (2000) exposed the test organism to the test material at measured concentrations < 1.3, < 1.3, 1.8, 5.2, 18, 56 and 190 ng/L, where controls were run concurrently for comparison. A preliminary study was performed to assess the stability of the test solution and define the dosing range. As a result the test protocol was revised to include renewal of the test solution every second day. Test concentrations were analysed by HPLC and LSC. Under the conditions of the test, adverse effects were observed at all concentrations tested, producing statistically significant reductions in frond number with a clear dose response pattern. Frond production and normal frond number was notably decreased at concentrations ≥ 56 ng/L during exposure. During the recovery period plants previously exposed to concentrations of the test material ≤ 18 ng/L produced normal fronds at a rate equivalent to those of the control. Plants exposed to 56 ng/L recovered much slower, whereas plants exposed to 190 ng/L did not recover at all. The 14 day IC10, IC50 and IC90 values were determined to be 15, 25 and 43 ng/L, respectively. The NOEC was determined to be <0.20 ng/L. Of the available data the results obtained in this study are the most sensitive and based on the worst case scenario have been identified as those most representative of the effects of the test material.

Desjardins et al. (2006) exposed Lemna gibba to the test material at the following measured concentrations; 1.7, 4.5, 11, 28, 67 and 168 ng/L, with a negative control run concurrently for comparison. All test concentrations were analysed and confirmed by HPLC and LSC, using the measured concentrations for interpretation of the results. Under the conditions of the test, exposure to the test material produced statistically significant reductions (p<0.05) in frond number and growth rate at the 67 and 168 ng/L. Treatment related effects were apparent at these two dose levels. The 7 Day EC50 for frond number and growth rate, were 53 and 76 ng/L. The 14 Day EC50 for both frond number and growth rate, were 54 and 106 ng/L. The day 7 and 14 NOAEC and LOEC were 28 and 67 ng/L, respectively.

Knauer (2002) was performed using the freshwater aquatic plant, Glyceria maxima variegate. The plants were exposed to the test material under static conditions for 28 days at nominal concentrations of 0.0003, 0.001, 0.003, 0.01, 0.03, 0.1 and 0.3 mg/L, with a negative control run concurrently for comparison. The test solution concentrations were verified periodically throughout the study by HPLC. Percentage recoveries of the test material were observed to decrease between Day 4 and 28. Resulting in an average recovery of between 66.7 and 100% of the nominal concentration over the whole exposure duration, thus the nominal concentrations were used to interpret the results. Under the conditions of the test, both biomass and plant height were significantly reduced when plants were exposed to the test material over 28 days under static conditions. The most sensitive endpoint was biomass, as dry weight, where plants displayed significant reduction at nominal concentrations of > 0.0003 mg/L, with a coefficient of variance of 36% by the end of exposure. The NOEC and EC₅₀ were determined to be 0.003 and 0.0206 mg/L for biomass, respectively. By Day 28 there was a significant reduction in plant height at nominal concentrations > 0.001 mg/L in comparison to the control. The coefficient of variance for all plants at the end of exposure was 17%. The NOEC and EC50 were determined to be 0.001 and 0.0047 mg/L for plant height, respectively. There was no incidence of necrosis or chlorosis observed in any treatment level during the study.

With the exception of Knauer (2002) all concentrations were representative of the active ingredient and were corrected for sample purity.

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).

Palmer et al (2001) and Desjardins (2006) were selected as the key studies for this endpoint and the key value for risk assessment was calculated as the geometric mean of the results of these two studies. These studies were selected as the key studies based on the robustness of their study design. Both studies were performed to a high standard to a standard guideline with a good level of detail in the reporting of the methods and results. Both studies employed a static-renewal test system and the concentrations quoted in the study were analytically confirmed.

Knauer (2002), performed on Glyceria maxima variegate (reed sweet grass) was found to be a less sensitive compared to Lemna gibba (duckweed). This study was therefore presented as supporting information, and Lemna gibba (duckweed) was selected for risk assessment purposes representative of a worst-case effect. Kranzfelder (2000), although performed to a similar method to the two key studies, only counted normal fronds, which may have led to an overestimation of the effects when compared to the key studies. As Kranzfelder (2000) does not refute the effects noted in the key studies, it is provided as supporting information. Sutherland et al (2000), unlike the other studies performed on Lemna gibba did not perform any test media renewals during the test. As the test substance was shown to degrade in the other studies performed to evaluate the toxicity of the test material in aquatic plants, and no additional analysis of test solutions were performed during or after the study, even though the type of media used in this study was different, the assumption that the actual concentrations are sufficiently represented by the nominal test concentrations is inappropriate. The study was therefore provided as supporting information, as though the effect levels may not be used for risk assessment, the effects observed during the study still provide useful information in the assessment of the toxicity of the test substance to Lemna gibba.

The available data are considered to be complete and a geometric mean value of 49.9 ng/L from the 14 day NOEC values from Palmer et al (2001) and Desjardins (2006) has been taken forward for risk assessment.