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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:
30 June to 28 July 2020.
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)
GLP compliance:
yes
Details on sampling:
- Concentrations:
- Sampling method: , a subsample from each test sample was analyzed on day 0 using gas chromatography with mass selective detection and electron impact ionization (GC MSD/EI) for confirmation of test substance identity and concentration, after extraction with acetonitrile/water (80/20, v/v) and partitioning with cyclohexane. Samples were analyzed using a validated GC-MSD/EI method
Vehicle:
no
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: Speyer 2.3 soil collected by Lufa-Speyer in Germany on 19 May 2020
- Other: The soil was collected from the top 20 centimeters of the field and passed through a 2-mm sieve.

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method:
Six 1.0-kg (dry weight equivalent) batches of soil were weighed out into beakers. Starting with the control, each batch of soil was dosed and mixed as follows. Approximately half of the soil batch was transferred to a 4-L jar. An appropriate amount of the test substance was dosed dropwise across the soil surface using a Hamilton gas tight syringe. The remaining half of the soil batch was then added to the 4-L jar. The soil was mixed by rolling the capped jar for approximately 3 hours at approximately 15 rpm on a rolling mill. The fortified soil was transferred to the bowl of a food mixer and mechanically mixed for 10 minutes at low speed. During this mechanical mixing, the soil was amended with 5.0 g of lucerne meal (i.e. alfalfa). Also, during this mechanical mixing, a volume of purified reagent water was added to the soil in order to bring the moisture content to 45 ± 5% of the soil’s maximum water holding capacity. After dosing and mixing, each batch of soil was divided equally into three replicate test samples in 1-L glass bottle test vessels.
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
19.9 to 21.4 °C
Moisture:
45 ± 5%
Details on test conditions:
TEST SYSTEM

- Test container (type, material, size): 1L glass bottle vessels, covered with perforated parafilm to allow for air exchange while reducing water loss
- Amount of soil: 1kg per vessel
- No. of replicates per concentration: 3
- No. of replicates per control: 3
- No. of replicates per vehicle control: n/a

SOIL INCUBATION
- Method: series of individual subsamples

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): Offenbach,
Rheinland-Pfalz, Germany
“rechts der Landauer Str.”, No. 826/7

- History of site: N/a
- Vegetation cover: N/a
- Treatments with pesticides or fertilizers: Over the past 4 years, no pesticides or organic fertilizers have been applied to the collection site.
- Depth of sampling: The soil was collected from the top 20 centimeters of the field

- pH (in water): 6.1
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): 54.2 - 56.6 mg/kg
- Maximum water holding capacity (in % dry weight): 26.5 g/100g dry soil
- Cation exchange capacity (mmol/kg): 5.9meq/100 g
- Storage (condition, duration): Before use, the soil was transferred to an environmental chamber set to maintain a temperature of 20 °C and allowed to equilibrate to incubation conditions for 2 to 28 days (11 days, actual).
- Initial microbial biomass as % of total organic C: 1.59

DETAILS OF PREINCUBATION OF SOIL (if any):

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : nitrogen transformation rate

VEHICLE CONTROL PERFORMED: no

Nominal and measured concentrations:
Nominal: 1.2, 3.7, 11, 33, and 100 mg a.i./kg dry weight soil.
Measured: 1.4, 3.9, 12, 32, 96 mg/kg
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
> 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
nitrate formation rate
Details on results:
- Effect concentrations exceeding solubility of substance in test medium: not observed
Reported statistics and error estimates:
Results of statistical analysis for significant differences from the untreated control: Kruskal-Wallis test

Mean nitrogen concentration and formation rates after a 28 day exposure.

Test system (mg/kg)

Day 0 Mean nitrogen concentration (mg/kg)

Day 28 Mean nitrate concentration (mg/kg)

Mean nitrogen formation rate (mg/kg/day)

Untreated control

54.3

183

4.61

1.2

54.2

198

5.14

3.7

54.9

181

4.5

11

56.6

189

4.74

33

54.7

174

4.27

100

55.7

185

4.61

Validity criteria fulfilled:
yes
Conclusions:
A 28-day EC50 value of >100 mg/kg soil dry weight, an EC10 value of >100 mg/kg soil dry weight and a NOEC of ≥100 mg/kg soil dry weight have been determined for the effects of the test substance on nitrogen formation rate of soil microflora.

Description of key information

28-day EC50 >100 mg/kg soil dry weight, EC10 >100 mg/kg soil dry weight and NOEC ≥100 mg/kg soil dry weight, effects of the test substance on nitrogen formation rate of soil microflora.

Key value for chemical safety assessment

Additional information

An OECD TG 216 soil microorganism test has been conducted with the registration substance according to ECHA final decision TPE-D-2114497761-36-01/F. The draft study report for the test is available, although this may be subject to change depending on the final report.

A 28-day EC50 value of >100 mg/kg soil dry weight, an EC10 value of >100 mg/kg soil dry weight and a NOEC of ≥100 mg/kg soil dry weight have been determined for the effects of the test substance on nitrogen formation rate of soil microflora, in accordance with test guideline OECD 216 and in compliance with GLP (Smithers, 2020). 

The chemical safety assessment will be updated once the study is finalised.

 

Until the final report is available, terrestrial data have been read across from the siloxane decamethylcyclopentasiloxane (D5, CAS 541-02-6) to derive an interim PNECsoil for hazard assessment.

See IUCLID Sections 6.0 and 6.3 (CSR Sections 7.0 and 7.2) for further discussion.