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Toxicity to soil microorganisms

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Description of key information

In a study according to OECD test guideline 216 under GLP, the toxicity of the test substance to soil microorganisms was determined to be 0.53 g/kg soil dw (EC10), 0.87 g/kg soil dw (EC20) and 2.29 g/kg soil dw (EC50), respectively.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:
2 290 mg/kg soil dw
Long-term EC10 or NOEC for soil microorganisms:
530 mg/kg soil dw

Additional information

The toxicity of the test substance to soil microorganisms was investigated in a study according OECD test guideline 216 under GLP.

A freshly collected and sieved sandy loam field soil (standard soil Lufa 2.3) was used for the test. The soil was amended with finely ground lucerne grass green meal (5.0 g kg-1soil dry mass). Five test item concentrations were tested: 0.10 g, 0.316 g, 1.00 g, 3.16 g and 10.0 g kg-1soil dry mass. Respective amounts of the test item were diluted in water and mixed into portions of the soil. Each treatment was set up withthreereplicates, each in appropriate glass vessels and incubated for a test period of 28 days at 20 ± 2°C in the dark.

Variability in the control revealed a maximum deviation from the mean nitrate concentration of 2.4%. Therefore, the validity criterion of a variability of less than 15% within the control given by the guideline was fulfilled. Nitrate extracted from soils treated with test item at 0.1 g/kg soil and 0.32 g/kg soil exceeded the nitrate concentration in extracts from the untreated controls by 20% and 61%, respectively. In view of the inherent variability of microbiological test systems, the ecological relevance of this observation remains doubtful.

At test item concentration of 1.0 g/kg, 3.2 g/kg and 10.0 g/kg soil nitrate concentration in the extracts was reduced by 18%, 73% and 76%, respectively, compared to the control. In treatment 1.0 g/kg soil one of the three replicates showed very unreliable results which were considered as outlier and therefore excluded from further calculations.Effective concentrations EC10, EC20and EC50of the test item for the endpoint nitrate concentration on day 28 determined by probit analysis were calculated to be 0.53 g/kg soil, 0.87 g/kg soil dw and 2.28 g/kg soil dw, respectively.