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Toxicity to soil microorganisms

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Description of key information

In a key study (BioChem agrar, 770828, 2015) according to OECD 2017 (2000) the NOEC of the test substance for effects on respiration in sandy loam soil is estimated to be ≥ 20 mg/kg soil dry weight. In addition in another key study (BioChem agrar, 770829, 2015) according to OECD 216 (2000) the NOEC of the test substance for effects on the soil nitrogen transformation (measured as NO3-N production) is estimated to be ≥ 20 mg/kg soil dry weight.

Key value for chemical safety assessment

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

Additional information

In a laboratory test (BioChem agrar, 770828, 2015) according to OECD 2017 (2000), soil microorganisms were exposed to the test substance for 28 days in a sandy loam soil (2 mm sieved, 8.9, 28.8 and 62.3 % particles in the <2, 2 - 50 and > 50 - 2000 µm size class, pH (H2O) 6.4, 1.44 % organic carbon, microbial biomass 49.95 mg C/100 g soil dry weight (i.e. 3.47 % of the total soil organic carbon)). The test was conducted in steel vessels covered with a lid, containing 1000 g dry soil. Nominal treatment rates were 2.0 and 20 mg/kg soil dry weight. Control soil was treated in the same way, but without the addition of test substance. A positive control (Dinoterb, 6.80, 16.00 and 27.00 mg/kg) was tested in a field soil in a separate test. Samples for determination of respiration rate were removed from the replicates on the day of dosing and after 7, 14 and 28 days. No adverse effects of the test substance on carbon transformation in soil could be observed at both test concentrations (2 mg/kg dry soil and 20 mg/kg dry soil) after 28 days. Only negligible deviations from the control of -0.4% (test concentration 2 mg/kg dry soil) and -3.6% (test concentration 20 mg/kg dry soil) were measured at the end of the 28-day incubation period. the NOEC of the test substance for effects on respiration in sandy loam soil is estimated to be ≥ 20 mg/kg soil dry weight.

In addition in a laboratory test (BioChem agrar, 770829, 2015) according to OECD 216 (2000), soil microorganisms were exposed to the test substance for 28 days in a sandy loam soil also (2 mm sieved, 8.9, 28.8 and 62.3% particles in the < 2, 2 - 50 and > 50 µm size class, according to USDA, pH (H2O) 6.4, 1.44% organic carbon, microbial biomass 49.95 mg C/kg dry soil (i.e. 3.47% of the total soil organic carbon)). The test was conducted in test vessels permitting air exchange, each containing 200 g dry soil. Nominal treatment rates were 2.0 and 20 mg/kg soil dry weight. Control soil was treated in the same way, but without the addition of test substance. A positive control (Dinoterb, 6.8, 16 and 27 mg/kg soil d.w.) was tested with soil from the same collection site in a separate test. Samples for determination of mineral nitrogen were removed from the replicates on the day of dosing and after 7, 14 and 28 days. Soil nitrogen transformation (measured as NO3-N-production) in treated soil differed from those in control soil by ≤ 4.0 % at any sampling time for the 2 mg/ kg soil dry weight and by ≤ 6.6 % at any sampling time for the 20 mg/kg soil dry weight. The NOEC of the test substance for effects on the soil nitrogen transformation (measured as NO3-N production) is estimated to be ≥ 20 mg/kg soil dry weight.