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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:
2020-01-29 to 2020-03-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: control, 10, 31.6, 100, 316, 1000 mg active acid/kg soil dry weight
- Sampling method: solid phase extraction, then photometric determination
- Sample storage conditions before analysis: Not reported
Vehicle:
no
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: A field fresh, silty sand soil (LUFA standard soil 2.3) was used in the study. Nominal soil parameters were:
Sand content 50 - 75 %
pH value 5.5 - 7.5
Organic carbon content 0.5 - 1.5 %
Microbial biomass (expressed as carbon content) at least 1 % of the total soil organic carbon.No crop protection products were used for a minimum of one year before sampling. No organic fertiliser was applied for at least six months prior use.


APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: The test item was weighed out and diluted in demineralized water for each test concentration separately and applied to the surface of the soil. The soil was mixed thoroughly with a mixer (approximately 3 minutes) to ensure a homogeneous distribution of the test item in the soil. Afterwards, the soil was distributed to the replicates.

VEHICLE: N/a
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
20 ± 2 °C
Moisture:
At experimental starting the pre-moistened soil was adjusted to approximately 45 % of its maximum water holding capacity. All replicates were weighed once per week to check for water losses by evaporation (recommended maximum 5 %, actual 0.2 - 1.5 %). Compensation with demineralized water was done. Replicates were weighed for this procedure.
Details on test conditions:
TEST SYSTEM
- Testing facility: Noack Laboratorien GmbH, Käthe-Paulus-Str. 1, 31157 Sarstedt, Germany
- Test container (type, material, size): Plastic boxes (volume 1.0 L, food grade) with perforated tops to enable gas exchange. Incubation was performed in bulk and sub-samples were taken.
- Amount of soil: 450 g soil dry weight
- No. of replicates per concentration: 3
- No. of replicates per control: 3
- No. of replicates per vehicle control: n/a

SOIL INCUBATION
- Method: bulk / series of individual subsamples

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude):
- History of site:
- Vegetation cover:
- Treatments with pesticides or fertilizers:
- Accidental contamination:
- Other:
- Depth of sampling: 0-20 cm
- Soil texture: silty sand (uS)
- % sand: approx. 58%
- % silt: approx. 35%
- % clay: approx. 7.3%
- Soil taxonomic classification: LUFA soil
- Soil classification system: LUFA soil 2.3, Batch number F2.31820
- pH (in water): 6.1 +/- 0.4
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight):
- Maximum water holding capacity (in % dry weight):35.2 ± 1.8g/100g DW
- Cation exchange capacity (mmol/kg): 6.8 ± 1.4 meq / 100 g
- Pretreatment of soil: The soil amounts were amended with powdered lucerne-green-grass-meal (0.5 % of soil dry weight).
Total nitrogen content: 24.6 g/kg
Total carbon content: 43.9 %
C/N ratio: 17.8

- Storage (condition, duration): The soil was stored for 2 days (2020-05-05 to 2020-05-07) in the dark at 4 - 6 °C in a climatic room. Subsequently, the soil was pre-incubated at room temperature (ca. 20 °C) for 21 days
(2020-05-07 to 2020-05-28) to adapt the micro-organisms to test conditions before the start of the study.

- Initial microbial biomass as % of total organic C: 2.26%

DETAILS OF PREINCUBATION OF SOIL (if any):N/a

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Nitrate-N content increase compared toc ontrol: every 7 days. Nitrate-N formation rate at 7d, 14d, and 28d

VEHICLE CONTROL PERFORMED: n/a

RANGE-FINDING STUDY
- Test concentrations: 0, 100, 1000 mg active acid/kg dry weight
- Results used to determine the conditions for the definitive study: yes
Nominal and measured concentrations:
Nominal: control, 10, 31.6, 100, 316, 1000 mg active acid/kg soil dry weight
Reference substance (positive control):
yes
Remarks:
Cyanoguanidine
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
54.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
other: active acid
Basis for effect:
nitrate formation rate
Remarks on result:
other: 95% C.I. <10 - 128
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
802 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
other: active acid
Basis for effect:
nitrate formation rate
Remarks on result:
other: 95% C.I. 558 - >1000
Details on results:
- Effect concentrations exceeding solubility of substance in test medium: No
- Other: N/a
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- Relevant effect levels: at 25 mg/kg soil dry weight, 28d of 32% difference to control in Nitrate-N, 39% in nitrate-n formation rate
- Other:
Reported statistics and error estimates:
ECx values were calculated by sigmoidal dose-response regression using GraphPadPrism. Four parameter were used for dose-response fitting. Calculation of the confidence intervals for ED-values was carried out using standard procedures provided by GraphPadPrism.

Increase of Nitrate-N formation rate in soil containing HMDTMP(4 -7K) aqueous solution, relative to the control.

Nitrate-N Formation Rate

Test item concentration

Increase [%] compared to control

[mg a.i./kg DW]

7 d

14 d

28 d

10.0

33

13

4

31.6

71

31

14

100

61

31

7

316

65

30

36

1000

76

78

52

Validity criteria fulfilled:
yes
Conclusions:
The 28d EC10 value for the effects of HMDTMP(4-7K) on the nitrogen formation rate of soil microorganisms is 54.9 mg active acid/kg dry weight (95% C.I of <10 - 128)

Description of key information

28d EC10 54.9 mg active acid/kg dry weight, reliability 1, soil microorganisms (Noack, 2020).

This study is currently in draft format and in accordance with ECHA/NR/20/33. The values are not expected to change in the final study report.

Key value for chemical safety assessment

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

Additional information

A 28-d EC10 value of 54.9 mg active acid/kg soil dry weight has been determined for the effects of HMDTMP-(4-7K) on the nitrogen formation rate of soil microorganisms, based on nominal concentrations. An EC50 value of 802 mg active acid/kg soil dry weight based on nitrogen formation has also been reported in the same study (Noack, 2020).