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Toxicity to soil microorganisms

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Description of key information

Key study, guideline BBA Part VI, 1-1 (1987), Nitrification in soils, Blumenstock (1989) :

NOEC >= 100 mg/L (in loamy sand and silt, based on nominal concentrations). The influence of the herbicide on the nitrification was of short duration only : the retardation of nitrification disappeared 90 days after treatment.

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
100 mg/kg soil dw

Additional information

The aim of this study was to study the influence of 20 and 100 mg a.i. of Aminotriazol Bayer/kg dry weight of soil, on the nitrification of added ammonium, on two different soils.

Aminotriazol Bayer (50% of active ingredient Amitrole) was applied in a dosage of 30 kg/ha (equivalent to ca. 40 mg formulation or 20 mg a.i./ kg dry weight of soil.

This amount of Aminotriazol Bayer and the 5-fold overdose induced a slight reduction of nitrification in a loamy sand (0.84% org. C, pH (KCl) = 5.3) and a silt (1.23 % org. C, pH (KCl) = 4.8). This effect had disappeared within 90 days after treatment. According to the results obtained in this study, a No Observed Effect Concentration (NOEC) >= 100 mg/L was found. In the treated samples of the loamy sand a small increase in nitrate formation (which was due to a simulation of native soil nitrogen) was measured at the end of the study. When applied as recommended, Aminotriazol Bayer should have no meaningful effects on nitrification in field soils.

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