Nitrapyrin

Toxicity to aquatic plants other than algae

Description of key information

7-day ErC50 ( growth rate - based on frond density) = 6.7 mg/L;

7-day ErC50 ( growth rate - based on frond dry weight) = 5.2 mg/L (empirical estimation);

7-day NOEC ( growth rate - based on frond density) = 2.4 mg/L;

7-day NOEC ( growth rate - based on frond dry weight) = 1.2 mg/L; freshwater duckweed (Lemna gibba), Softcheck (2014)

Key value for chemical safety assessment

EC50 for freshwater plants:

5.2 mg/L

EC10 or NOEC for freshwater plants:

1.2 mg/L

Additional information

The toxicity of the test material to the freshwater duckweed, Lemna gibba, was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guideline OCSPP 850.4400.

During the studyan inoculum of 12 fronds (plants with three to four fronds each) was aseptically introduced into each test vessel. Fronds were transferred on days 3 and 5 to newly prepared test solutions during the exposure in an attempt to maintain the solution concentrations and replenish nutrients used in plant growth. Test solutions were prepared at each renewal period and plants were placed in newly assigned random positions in the environmental chamber. On days 3, 5 and at test termination (day 7), fronds were counted and observations were made after each observation period. The test vessels were assigned new random positions on a single shelf within the environmental chamber after the 3- and 5-day observation intervals. At test termination (day 7), after frond density determinations were complete, the fronds were removed from each vessel, blotted dry and transferred to preweighed aluminum pans. Fronds were dried in an oven at a temperature of 66 to 71 ºC for nine days prior to dry weight determination.

Following a 7-day exposure of Lemna gibba to test material, the 7 day NOEC and LOEC values for yield (based on frond density) were determined to be 2.4 and 4.6 mg/L, respectively. The EyC50 value was determined to be 4.3 mg/L, with 95 % confidence limits of 3.8 to 5.2 mg/L.

The 7 day NOEC and LOEC for growth rate (based on frond density) were determined to be 2.4 and 4.6 mg/L, respectively. The ErC50 value was determined to be 6.7 mg/L, with 95 % confidence limits of 6.0 to 7.5 mg/L.

The 7 day NOEC and LOEC for yield (based on frond dry weight) were determined to be 1.2 and 2.4 mg/L, respectively. The 7-day EyC50 value was determined to be 3.5 mg/L, with 95 % confidence limits of 3.2 to 3.8 mg/L..

The 7 day NOEC and LOEC for growth rate (based on frond dry weight) were determined to be 1.2 and 2.4 mg/L, respectively. The 7-day ErC50 value was determined to be 5.2 mg/L, with 95 % confidence limits of 4.4 to 5.8 mg/L.

The validity criterion for performance of Lemna were met with the CV for 7-day control yield and growth rate 6.9 % and 2.4 %, respectively, the doubling time of frond numbers in the control being 1.7 days and the 7-day mean control frond density being 212 fronds/replicate.