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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
yes
Remarks:
Deviations were not considered to imact the outcome, quality or integrity of the study
Principles of method if other than guideline:
Deviations: The soil was stored at 6 ± 2°C instead of 4 ± 2°C as the climatic chamber for storage of amounts of >5 kg cannot be adjusted to lower temperatures (technical reasons).
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Batch number: 1518148
Purity: 92.66%
Analytical monitoring:
not required
Vehicle:
no
Details on preparation and application of test substrate:
Soil: Field fresh, silty sand soil (LUFA soil 2.3 - LUFA Speyer, Obere Langgasse 40, 67346 Speyer, Germany).
Sample site: Site was not treated with crop protection products for at least 1 year before sampling, organic fertiliser for at least 6 months before sampling or mineral fertiliser for at least 3 months before sampling.
Preparation: Soil was sieved to 2 mm and adjusted to approximately 42% of its maximum Water Holding Capacity. Soil was checked for detectable microbial biomass and amended with lucerne-grass-green-meal (0.5% SDW).
Storage: Soil was stored for 92 days at 6 ± 2°C in a climatic room before pre-incubation at room temperature (approximately 20°C) for 24 hours before exposure.
Application: Respective amounts of test item were pipetted onto quartz sand (1% of total soil amount per treatment), mixed thoroughly and applied to the surface of the soil. Soil was adjusted to 45% WHCmax with demineralised water and mixed with an electric mixer before distribution into the replicates.
Soil parameters:
Sampling depth: Approximately 20 cm
pH 5.7 ± 0.6
SDW before application 87.0 g/100 g soil
Maximum water holding capacity: 35.4 ± 1.5 g/100 g DW
Sand: 57.6%
Silt: 35.9%
Clay: 6.6%
Microbial biomass: 3.78 % total organic carbon
CEC: 7.5 meq/100 g
Test organisms (inoculum):
soil
Total exposure duration:
29 d
Test temperature:
21-22°C
Moisture:
At the start of the experiment premoistened soil was adjusted to approximately 45% of the maximum water holding capacity. All replicates were checked once per week for losses. Demineralised water was added as neessary.
Moisture: 41.9-43.4% WHC max
Details on test conditions:
TEST SYSTEM
Test container: 1 L food grade plastic boxes with perforated tops
Amount of soil: 400 g SDW per replicate
No. of replicates per concentration: 3
No. of replicates per control: 3
Incubation method: Bulk
Photoperiod: Dark
pH: 6.73-7.00
SDW: 86.8-87.1%

EFFECT PARAMETERS MEASURED: Measurements of inorganic nitrate were carried out on days 0, 7, 14 and 29. Nitrate was extracted from soil with a mineral salt medium (potassium chloride) and cleaned with C18-SPE cartridges (conditioned with methanol and demineralised water). Nitrate-nitrogen concentrations were determined photometrically (588 nm). Potassium nitrate was prepared in demineralised water as an extraction standard. LOQ for nitrate-N: 1.74 mg NO3-N/kg SDW.

RANGE FINDING STUDY
Range finding study: Yes, 1, 10, 100 mg/kg SDW
Nominal and measured concentrations:
Nominal: 1000, 500, 250, 125, 62.5 mg/kg soil dry weight
Control: Untreated soil
Reference substance (positive control):
yes
Remarks:
Cyanoguanidine
Key result
Duration:
29 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
Details on results:
No inhibiting effects on the nitrification potential were seen at the highest concentration tested 1000 mg/kg soil dry weight. Enhancing effects in respect to an increase of the nitrification potential could be observed in a concentration dependent manner, trailing off over the exposure time.
Results with reference substance (positive control):
Reference substance concentration of 50mg/kg soil dry weight saw 82% nitrate-N formation rate compared to the untreated control. At a concentration of 100 mg/kg soil dry weight there was a 92% nitrate-N formation rate compared to the untreated control.
Reported statistics and error estimates:
Normality and equal variance were tested (p=0.05) then one way analysis of variance (ANOVA) was carried out to determine statisticially significant differences between the treatments and the control replicates.
No statistical calculations were performed to derive EC values as no inhibition was detected.
Validity criteria fulfilled:
yes
Remarks:
Variation between the control replicates was <15% at days 0, 7, 14 and 29 for determination of the nitrate-N content.
Conclusions:
DPCD showed no inhibiting effects on the nitrification potential up to a concentration of 1000 mg/kg SDW. The NOEC can thus be considered equal or higher than 1000 mg/kg SDW and the EC10 can be considered higher than 1000 mg/kg SDW.
Executive summary:

The effect of DCPD on the nitrification of soil microorganisms was determined in a GLP-compliant study following OECD guideline 216. No inhibiting effect on the nitrification potential was observed up to a concentration of 1000 mg/kg SDW, the highest concentration tested. The NOEC is therefore considered to be =1000 mg/kg SDW.

Description of key information

DPCD showed no inhibiting effects on the nitrification potential up to a concentration of 1000 mg/kg SDW. The NOEC can thus be considered equal or higher than 1000 mg/kg SDW and the EC10 can be considered higher than 1000 mg/kg SDW.

Key value for chemical safety assessment

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

Additional information

The effect of DCPD on the nitrification of soil microorganisms was determined in a GLP-compliant study following OECD guideline 216. No inhibiting effect on the nitrification potential was observed up to a concentration of 1000 mg/kg SDW, the highest concentration tested. The NOEC is therefore considered to be =1000 mg/kg SDW.