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Toxicity to soil microorganisms

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Reference
Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Study period:
19 Oct - 22 Nov 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP Guideline study
Qualifier:
according to
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.21 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Swiss Federal Office of Public Health, Bern, Switzerland
Analytical monitoring:
no
Vehicle:
no
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: lucerne meal (containing approx. 2.5% nitrogen and had a C:N ratio of 16:1).

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: Prior to test start, the application solution of the highest test concentration was prepared by mixing 7.2 g of the test substance in 300 mL of purified water. An aliquot of this application solution was further diluted in purified water to obtain the application solutions for the lower test concentrations. For treatment, 663 g soil (equivalent to 600 g dry soil) and 3.0 g Lucerne meal were mixed in a Hobart mixer and treated with 25 mL of the respective application solution. The application solutions were added slowly to the soil during mixing for about five minutes. The test item treated soil was sieved through a 4 mm sieve and aliquots of 150 g dry soil were weighed into incubation flasks. Finally, the moisture content of the soil was adjusted to 45% of the water-holding capacity by adding purified water. Control soil aliquots were handled equally to the test item treatments, except for the addition of the test item (10 mL of purified water was applied).
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
20 ± 2 °C
Moisture:
45% of the water-holding capacity
Details on test conditions:
TEST SYSTEM
- Testing facility: laboratory
- Test container (type, material, size): For each treatment and sampling time, one soil aliquot was set-up in a 1 L incubation flask
- Amount of soil: 150 g dw
- No. of replicates per concentration: 3
- No. of replicates per control: 3

SOIL INCUBATION
- Method: All samples were incubated in the dark. The temperature was monitored continuously. The moisture content of the soil aliquots was monitored on a weekly basis and moisture loss was compensated by the addition of purified water to maintain 45% of the soil MWC until the end of incubation.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site: Landwirtschaftliche Untersuchungs- und Forschungsanstalt (LUFA), Speyer, Germany
- Treatments with pesticides or fertilizers: The soil had not been subjected to any pesticide treatment in the sampling year and four former years. Furthermore, neither organic fertilizers not mineral fertilizers were applied in the sampling year and four former years.
- Other: The soil was uncultivated in the sampling year and four former years.
- Depth of sampling: 20 cm
- Soil texture (USDA)
- % sand: 63.1%
- % silt: 28.4%
- % clay: 8.5%
- Soil texture (DIN)
- % sand: 60.3%
- % silt: 31.1%
- % clay: 8.6%
- Soil taxonomic classification: sandy loam
- Soil classification system: USDA
- pH (in water): 7.5
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): 49.1 mg/kg dry soil
- Maximum water holding capacity: 37.3 g/100 g
- Cation exchange capacity: 10.9 mval/100 g soil
- Pretreatment of soil: The soil was sieved through a 2 mm sieve by LUFA after sampling. After arrival, the soil was stored at 4 ± 2 °C in the dark for three weeks before use. Before test start, the soil was homogenized with a 5 mm sieve and equilibrated in the dark at 20 ± 2 °C at about 40% of the maximum water-holding capacity (MWC) for a period of 7 d. Prior to test item application, the soil moisture content was adjusted to just below 45% of the MWC. Furthermore, the pH of the soil in water, the initial nitrate content and the microbial biomass content of the soil was determined before test start.
- Initial microbial biomass as % of total organic C: 3.0%

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Formation of nitrate at day 0 and 28.
Nominal and measured concentrations:
nominal: control, 10, 32, 100, 320, 1000 mg/kg soil dw
Reference substance (positive control):
yes
Remarks:
Nitrapyrin
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Results with reference substance (positive control):
EC50 (28 d): 6.1 mg/kg soil dw

Microbial Biomass

The maximum rate of initial CO2 evolution from untreated soil was at average 0.698 mL per hour and 100 g dry soil. The microbial biomass was calculated to be 283 mg microbial carbon/kg dry soil, corresponding to 3% of the total organic carbon in the soil.

 

Nitrification of the Lucerne meal

The initial nitrate content of the soil was determined to be 56 mg nitrate (NO3-) per kg dry soil. At day 0, the average nitrate concentrations in Lucerne meal amended soil ranged between 53 and 60 mg NO3-/kg dry soil in all treatments and the control. The calculated deviations to the control were +2.2 to +12%.

At day 28, the nitrate concentration in the control had increased to 128 mg NO3-/kg dry soil. Nitrate concentrations in the test item treatments ranged between 125 and 186 mg NO3-/kg dry soil corresponding to deviations from the control of -2.2 to +46%. None of the concentrations showed inhibition of the nitrogen transformation activity.

Description of key information

NOEC (28 d): ≥ 1000 mg/kg soil dw for soil microorganisms (OECD 216)

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
1 000 mg/kg soil dw

Additional information

One study is available investigating the effects of Atmer 163 (CAS No. 97925-95-6) on the nitrification of Lucerne meal. The study was performed according to OECD 216 (GLP; Eckenstein, 2013). Nominal concentrations up to 1000 mg/kg soil dw were tested for 28 d. At day 28, the nitrate concentration in the control had increased to 128 mg NO3-/kg dry soil. Nitrate concentrations in the test item treatments ranged between 125 and 186 mg NO3-/kg dry soil corresponding to deviations from the control of -2.2 to +46%. None of the concentrations showed inhibition of the nitrogen transformation activity. Thus, the test substance has no long-term influence on nitrogen transformation in soils and a NOEC (28 d) ≥ 1000 mg/kg soil dw and an EC50 (28 d) > 1000 mg/kg soil dw were derived.