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Toxicity to soil microorganisms

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Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP guideline study with restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Qualifier:
according to guideline
Guideline:
OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test)
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
yes
Details on preparation and application of test substrate:
APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: The test substance was not soluble in water therefore a stock solution in acetone was prepared and applied onto quartz sand. 20 mg test substance was dissolved in 20 ml acetone. Appropiate ammounts of the solution were dropped onto quartz sand and after evaporation of the acetone, the quartz sand was mixed into the soil. For the control, only acetone treated quartz sand was mixed into the soil.

VEHICLE:
- Chemical name of vehicle: acetone
- Concentration of vehicle in test medium: 1 mg/L
- Evaporation of vehicle before use: yes
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
20-22 °C
Moisture:
Carbon Transformation Test: 49.3 - 51.5% soil water content related to WHCmax
Nitrogen Transformation Test: 48.9 - 51.8% soil water content related to WHCmax
Details on test conditions:
TEST SYSTEM
- Testing facility:
- Test container: disposable plasic boxes covered by perforated lids
- carbon transformation test: 1 L boxes (0.12x0.165x0.065 m)
- nitrogen transformation test: 0.5 L boxes (0.1x0.1x0.065 m)
- Amount of soil:
- carbon transformation test: 750 - 1000 g soil dw
- nitrogen transformation test: 250 - 500 g soil dw
- No. of replicates per concentration: 3
- No. of replicates per control: 3

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): 49° 51' 53" N; 8° 45' 28"' E
- History of site: for at least two years prior test initiation, no pesticides, no organic or mineral fertilizer had been applied to the soils
- Vegetation cover: fallow grassland
- Treatments with pesticides or fertilizers: none
- Accidental contamination: none
- Depth of sampling: 0.05 -0.2 m
- Soil texture
- % sand: 59.3
- % silt: 31.7
- % clay: 9.0
- Soil taxonomic classification: loamy sand
- Soil classification system: USDA and DIN 19683
- pH (in water): 6.9
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): 9.53
- Maximum water holding capacity (in % dry weigth): 48.9
- Cation exchange capacity (mmol Ba/kg dw): 44
- Initial microbial biomass as % of total organic C: 6.7

EFFECT PARAMETERS MEASURED:
- Respiration rate and nitrogen mineralisation and nitrification after 0 (within 6 h), 7, 14, 28 days




Nominal and measured concentrations:
Nominal test conentrations: control, 0.1, 1.0 mg/kg
Reference substance (positive control):
yes
Remarks:
sodium chloride
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
respiration rate
Remarks:
and nitrate formation rate
Details on results:
- Difference in soil respiration rates between the control and the treatments were < 25 %
- Soil nitrogen content: < 25% throughout the experiment
- Soil nitrate formation rate: -3.6% - -18.8% (days 14-28)

Results with reference substance (positive control):
Results of a seperate test (April - August 2006, 98 days):
- Respiration rates: -56.83% (day 28); -54.82% (day 98) from the control
- Soil nitrate content: -75.96% (day 28); -99.73% (day 98) from the control
- Nitrate formation rate: -130.2% (day 0-28); 112.3% (day 0-98) from the control

Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Non GLP - Guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
GLP compliance:
no
Vehicle:
no
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: Soil samples were amended with 0.5% lucerne meal (related to soil dry weight) before application in the transformation test.

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: Since the water solubility was low, the test item was thoroughly mixed with quartz meal. Subsequently the obtained mixture was added and mixed with the soil by means of a hand stirrer.

Test organisms (inoculum):
soil
Total exposure duration:
100 d
Remarks:
Since differences in nitrate content between treated and untreated soil were greater than the OECD trigger value of 25, measurements were continued to a maximum of 100 days.
Test temperature:
18.9 - 21.8°C
Moisture:
Approx. 45% of the maximum soil water holding capacity.
Measured values during the test: 15.51 – 16.48 g/100 g dry soil.
Details on test conditions:
TEST SYSTEM
- Testing facility:
- Test container (type, material, size): Wide mouth glass flasks; screw caps of the flask
- Amount of soil: 200 g soil dry weight
- No. of replicates per concentration: 3
- No. of replicates per control: 3


SOIL INCUBATION
- Method: Series of individual and equally sized subsamples of each treatment group in darkness.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): latitude 51.403774567° N, longitude 12.694435960° E) in Wassergut Canitz, Germany
- History of site: Biologically active agricultural soil (loamy sand according to DIN);
- Treatments with pesticides or fertilizers: Last application of plant protection products: 1990. No application of fertilisers since 2003.
- Depth of sampling: 20 cm
- Soil texture:
Classification DIN 4220/ISO 11277: loamy sand
< 2 µm (clay) 8.1
63 to ≥ 2 µm (silt) 38.9
≥ 63 µm to 2000 µm (sand) 53.0
Classification USDA: sandy loam
< 2 µm (clay) 8.1
50 to ≥ 2 µm (silt) 37.3
≥ 63 µm to 2000 µm (sand) 54.6
- pH (in water): 6.6
- Initial nitrate concentration for nitrogen transformation test: Total N (mg/kg dry weight) is 0.14
- Maximum water holding capacity: 45%
- Cation exchange capacity (mmol/kg): 86
- Initial microbial biomass as % of total organic C: 27.67 mg C/kg dry wt soil (1.88% of total organic carbon)


EFFECT PARAMETERS MEASURED: Nitrogen mineralization and nitrification was determined after 0 (within 3 hours), 14, 28 and 100 days.


Nominal and measured concentrations:
Nominal concentrations of 1, 5, 10, 30, 60, 100, 300, and 1000 mg a.s./kg dry weight (d.wt.) soil
Reference substance (positive control):
yes
Remarks:
Dinoterb
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
300 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.:
633.5 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Duration:
100 d
Dose descriptor:
NOEC
Effect conc.:
300 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Duration:
100 d
Dose descriptor:
EC50
Effect conc.:
829.1 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate

The test item caused a maximum inhibition of -60.4% and -56.8% at 1000 mg/kg dw soil 28 days and 100 days after application, respectively.

The coefficients of variation in the control were maximum 3.9% and thus fulfilled the demanded range (≤ 15%). The results on the reference substance in the most recent test demonstrate the sensitivity of the test system.

Description of key information

NOEC (28 d) = 300 mg/kg dw (nominal, nitrogen transformation)
EC50 (28 d) = 633.5 mg/kg dw (nominal, nitrogen transformation)

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:
633.5 mg/kg soil dw
Long-term EC10 or NOEC for soil microorganisms:
300 mg/kg soil dw

Additional information

To investigate the effects of OPP (CAS-No. 90-43-7) on soil respiration and nitrification of soil micro-organisms, two GLP study are available. In the first test the activity of soil microflora was investigated with regard to nitrogen transformation (mineralization) over a period of 100 days of exposure. This test was performed according to OECD Guideline No. 216 (Schulz 2012). A loamy soil enriched with Lucerne meal (concentration in soil 0.5%) was used.The test consisted of 10 treatment groups (including control) with three replicates each. Test item concentrations were the following: 1, 5, 10, 30, 60, 100, 300, and 1000 mg test item per kg soil dry weight. Nitrogen transformation (ammonium, nitrate and nitrite) was determined on day 0 (after approx. 3 hours) and at intervals of 14, 28 and 100 days after application.

The NOEC of OPP was calculated to be 300 mg/kg soil dry weight 28 days and 100 days after application. The EC50 was calculated to be 633.5 mg/kg and 829.1 mg/kg soil dry weight 28 days and 100 days after application, respectively.

The second test was performed according to OECD Guidelines No. 216 and 217 (Reis 2007). A loamy sand soil was tested and the test concentrations were 0.1 mg a.i./kg soil and 1.0 mg a.i./kg soil. The carbon transformation in soil after addition of glucose was measured by determining the CO2-production over a period of up to 24 hours at day 0, 7, 14 and 28 after treatment. For the nitrogen-transformation in soil enriched with lucerne meal (concentration in soil 0.5%), NH4-, NO2- and NO3-nitrogen concentrations were determined on day 0, 7, 14 and 28 after treatment. OPP has no impact on respiration and nitrogen transformation of soil microflora when applied up to 1.0 mg a.i./kg soil.