Nitrapyrin

Toxicity to terrestrial plants

Description of key information

3-week NOER = 1000 g a.i./ha, EPA OPP 123-1, EPA OPPTS 850.4100, Bergfield (2014)

NOER of 1000 g a.s./ha was converted to a NOEC of 1.33 mg/kg dwt at 5 cm soil depth and then converted to standard organic matter content of 3.4%) to give a NOEC of 1.78 mg/kg dwt

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for terrestrial plants:

1.78 mg/kg soil dw

Additional information

The toxicity of the test material to terrestrial plants was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guidelines EPA OPP 123 -1 and EPA OPPTS 850.4100.

Seven species of dicotyledonous plants and three species of monocotyledonous plants were selected based on taxonomic criteria. The dicotyledons tested were buckwheat – Fagopyrum esculentum, cabbage – Brassica oleracea, carrot – Daucus carota, cucumber – Cucumis sativus, lettuce – Lactuca sativa, soybean – Glycine max, and sugar beet – Beta vulgaris. The monocotyledons tested were onion – Allium cepa, corn – Zea mays, and ryegrass – Lolium perenne. Plantings were made with untreated seeds, at exaggerated density to allow reduction to uniform stand prior to application. The spray solutions were applied to the surface of the soil using an overhead sprayer. The apparatus was calibrated prior to use to provide the proper spray volume per surface area. The nominal application rates were 0 (control), 65.2, 125, 250, 500, and 1000 g a.i./ha. No surfactant was used. The nominal application volume was 200 liters of application solution per hectare. The control pots were sprayed with an equivalent amount of deionised water.

Data collected included percent emergence, post-emergent plant survival, visual injury (i.e., phytotoxicity), shoot length, and replicate shoot fresh weight at termination. The data were analysed using analysis of variance with Dunnett’s test to compare treatments to the control to determine the no effect rate (NOER). Where possible, non-linear regression analysis was used to estimate the effective rate to elicit a 25 and 50% detrimental effect (IR25 and IR50) for length and weight data.

Under the conditions of the study the NOER, ER25, and ER50 values for the effects of seedling emergence exposure to the test material formulation on plant emergence, survival, shoot length, and shoot fresh weight were greater than or equal to 1000 g a.i./ha.

Supporting data are available in the form of a publication which reported on the effect of the test material following application to lettuce, celery and strawberries. On strawberry fields, the coated fertiliser Osmocote was compared with nitrogen alone.

The lettuce experiment was conducted on Watsonville loam soil with low (6 to 8 ppm) nitrate-nitrogen residue. The beds were listed on 40-inch centers. Nitrogen rates used were 0, 60, 120, 180, and 240 pounds of N per acre, with and without test material. Those without were treated in split applications: half the ammonium sulphate was applied as a preplant sidedressing, and the other half was sidedressed after thinning. Plots with test material received their total nitrogen in a pre-plant band application.

Ammonium fertiliser without test material was applied in a split application to provide comparison with grower practices and to keep the number of plots at a manageable level. Previous experiments in several areas of California and Arizona have demonstrated that split applications of N are at least equal to a single application and, in some cases, have resulted in significant yield increases.

The test material appeared effective in delaying oxidation of NH4+ to the leachable nitrate form. Apparently, the test material helped increase availability of nitrogen to plant roots by reducing the leaching of nitrates beyond the effective rooting depth. This stabilisation of ammonium in a single application lasted long enough to grow crops of lettuce, celery, and first-year strawberries.