Nitrapyrin

Long-term toxicity to aquatic invertebrates

Description of key information

21-day NOEC (mortality) = 0.744 mg a.i./L; 21-day NOEC (reproduction) = 0.103 mg a.i./L (Daphnia magna), OECD 211, Rebstock (2013)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

0.103 mg/L

Additional information

The long term toxicity of the test material to aquatic invertebrates was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guideline OECD 211.

During the study Daphnia magna was exposed to test material at target nominal concentrations of 0 (negative control), 0 (vehicle control), 0.063, 0.13, 0.25, 0.50, and 1.0 mg a.i./L. The definitive test was conducted for 21 days commencing when daphnids were added to the test chambers. Daphnids were transferred with a pipet from the containers to the appropriate test chamber. The controls and all treatments were replicated 10 times. Observations were made daily on the number of surviving adult daphnids, occurrence of abnormalities, and production of neonates. Immobile daphnids, defined as those organisms not able to swim within 15 seconds after gentle agitation of the test vessel or gentle disturbance of the individual, were discarded; therefore, immobility was synonymous with mortality.

Test solutions were renewed every 2 to 3 days (Monday, Wednesday, and Friday) during the exposure. On each renewal day, the parent daphnids were transferred to clean test chambers containing freshly prepared test solutions. Transfers began with the control replicates and then proceeded from the lowest test material treatment to the highest test material treatment. After the release of broods by the adult daphnids, only the adult daphnids were transferred to fresh test solutions. The neonates produced between each renewal and at termination were counted and discarded.

At test termination, the length (head to base of spine) of each surviving adult was measured with a calibrated ocular micrometer on a Leica S6E dissecting microscope. Prior to the length measurements, the ocular micrometer within the dissecting microscope was calibrated against a stage micrometer. Therefore, the ocular measurements could then be converted to millimeters.

After 21 days of exposure, survival of D. magna exposed to test material was 100, 100, 100, 100, 90, 100, and 100% in the 0 (control), 0 (vehicle control), 0.0456, 0.103, 0.217, 0.441, and 0.744 mg a.i./L treatments, respectively. There was no statistically significant (p = 0.05) reduction in survival in any test material treatment, as compared to the pooled control (Dunnett’ test; p=0.05). Based on survival and time-weighted mean measured concentrations, the 21-day NOEC and LOEC values were 0.744 and >0.744 mg a.i./L, respectively. The 21-day EC50, based on immobilisation of the first generation daphnids was >0.744 mg a.i./L, the highest concentration tested.

The total numbers of live young produced by surviving first generation daphnids after a 21-day exposure were 2,398, 2,578, 2,458, 2,517, 1,979, 1,894, and 1,656 in the 0 (control), 0 (vehicle control), 0.0456, 0.103, 0.217, 0.441, and 0.744 mg a.i./L treatments, respectively. The mean number of live young produced per surviving adult during the course of the test was 240, 258, 246, 252, 220, 189, and 166 in the 0 (control), 0 (vehicle control), 0.0456, 0.103, 0.217, 0.441, and 0.744 mg a.i./L treatments, respectively. There were statistically significant reductions in mean number of live young produced per surviving adult in the 0.441 and 0.744 mg a.i./L treatments, as compared to the pooled control (Dunnett’s test; p=0.05). The mean day of first brood was 7.2, 7.1, 7.3, 7.2, 7.1, 7.2, and 7.1 in the 0 (control), 0 (vehicle control), 0.0456, 0.103, 0.217, 0.441, and 0.744 mg a.i./L treatments, respectively. There was no statistically significant increase in mean days to first brood in any test material treatment, as compared to the control (Dunnett’s test/Williams’ test; p=0.05). Based on time-weighted mean measured concentrations and the mean number of live young produced per surviving adult, the 21-day NOEC and LOEC were 0.103 and 0.217 mg a.i./L, respectively. The MATC for mean number of live young produced per surviving adult was 0.150 mg a.i./L. Based on time-weighted mean measured concentrations and the mean days to first brood, the 21-day NOEC and LOEC were 0.744 and >0.744 mg a.i./L, respectively.

Mean lengths of surviving first generation daphnids at test termination were 4.6, 4.6, 4.6, 4.6, 4.5, 4.3, and 4.1 mm for the 0 (control), 0 (vehicle control), 0.0456, 0.103, 0.217, 0.441, and 0.744 mg a.i./L treatments, respectively. There were statistically significant reductions in mean length of surviving adults in the 0.441 and 0.744 mg a.i./L, as compared to the pooled control (Dunnett’s test; p=0.05). The NOEC and LOEC values, based on time-weighted mean measured concentrations and adult length, were 0.217 and 0.441 mg a.i./L, respectively. The MATC for adult length was 0.309 mg a.i./L.