Dihexyl ether

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18 July to 26 August 2022

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)

Version / remarks:

Adopted January 21, 2000

Deviations:

yes

Remarks:

The temperature increased above the temperature range recommended by OECD guideline 216 to a high of 36.3 ℃ overnight from 27 to 28 July 2022.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

yes

Remarks:

Acetone

Details on preparation and application of test substrate:

A 100-mg/mL primary stock solution was prepared by dissolving 1.0143 g (1.0001 g active ingredient) of dihexyl ether in 10.0 mL of acetone. This 100-mg/mL stock solution was used to dose the dihexyl ether-treated soils.

Seven 10-g batches of quartz sand were prepared for the 1.0, 3.0, 9.0, 27, 81, and 243 mg/kg test substance, and control treatment groups. The nitrification sand was dosed with 0.1, 0.3, 0.9, and 2.7 mL of the 10-mg/mL dihexyl ether stock solution to achieve 1.0, 3.0, 9.0, and 27 mg/kg concentrations, respectively. To achieve the 81 and 243 mg/kg concentrations, the nitrification sand was dosed with 0.81 and 2.43 mL of the 100-mg/mL dihexyl ether stock solution, respectively. The solvent was allowed to evaporate off before the dosed sand was mixed into the soil. Seven 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 bowl of a Hobart mixer. An appropriate amount of the test substance was added across the soil surface while mixing the soil using the food mixer. The remaining half of the soil batch was then added to the bowl. The fortified soil was mechanically mixed for approximately 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:

The temperature was monitored continuously with a minimum/maximum thermometer, and ranged from 19 to 22 °C.

Moisture:

The soil moisture content was maintained at approximately 45 ± 5% of the maximum water holding capacity throughout the test. The moisture content of the soil samples was checked and adjusted, if necessary, once a week.

Organic carbon content (% dry weight):

0.64

Details on test conditions:

TEST SYSTEM
- Testing facility: Smithers
- Test container (type, material, size): 1-L glass bottles
- Amount of soil: 1 kg
- No. of replicates per concentration: 3
- No. of replicates per control: 3
- No. of replicates per vehicle control: 0

SOIL INCUBATION
- Method: bulk / series of individual subsamples: 3 replicates - The 1-L glass bottle test vessels were sealed with perforated parafilm, which allowed for air exchange and avoided loss in moisture. The samples were incubated at a temperature of 20 °C in a dark environmental climate chamber. The temperature was monitored continuously with a minimum/maximum thermometer, and ranged from 19 to 22 °C. The soil moisture content was maintained at approximately 45 ± 5% of the maximum water holding capacity throughout the test. The moisture content of the soil samples was checked and adjusted, if necessary, once a week.

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
- Treatments with pesticides or fertilizers: None used within the last 5 years
- Depth of sampling: Collected from the top 20 cm of the field
- Soil texture
- % sand: 63
- % silt: 28
- % clay: 9
- Soil taxonomic classification: Sandy Loam
- Soil classification system: USDA
- pH (in water): 6.4
- Maximum water holding capacity (g/100 g dry soil): 24.3
- Cation exchange capacity (meq/100 g): 6.1
- Pretreatment of soil: passed through a 2-mm sieve
- Storage (condition, duration): stored refrigerated (approximately 4 °C) and in the dark
- Initial microbial biomass as % of total organic C: 1.43

DETAILS OF PREINCUBATION OF SOIL (if any): Before use, the soil was transferred to an environmental chamber set to maintain a temperature of 20 ± 2°C and allowed to equilibrate to incubation conditions for 2 to 28 days (8 days, actual).

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Nitrate concentration at 0 and 28 d.

VEHICLE CONTROL PERFORMED: no - acetone evaporated off before use

Nominal and measured concentrations:

1.0, 3.0, 9.0, 27, 81, and 243 mg a.i./kg dry weight soil

Key result

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

3.3 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: difference was due to a stimulatory effect of the nitrate formation and not an inhibitory effect

Duration:

28 d

Dose descriptor:

EC25

Effect conc.:

46.6 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: difference was due to a stimulatory effect of the nitrate formation and not an inhibitory effect

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

3 752 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: extrapolated value since higher than highest concentration

Details on results:

No inhibitory effects were observed in the study, only a stimulatory effect of the nitrate formation

Validity criteria fulfilled:

yes

Conclusions:

The results of the study indicated that dihexyl ether had a stimulatory effect on the nitrate formation rate at the concentrations tested, resulting in an EC10 value of approximately 3.3 mg/kg. The EC25 and EC50 were determined to be 46.6 and 3752 mg/kg, respectively. The EC50 value was extrapolated since it was higher than the highest concentration tested.

Executive summary:

Dihexyl ether exposure did not result in inhibitory effects to nitrate rate formation in an OECD 216. Statistically significant stimulatory effects were observed at the two highest concentrations of 81 and 243 mg/kg.

Description of key information

Dihexyl ether was not inhibitory to the nitrate formation rate in an OECD 216 guideline study. Statistically significant stimulatory effects were observed at the two highest concetrations of 81 and 243 mg/kg.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:

3 752 mg/kg soil dw

Long-term EC10 or NOEC for soil microorganisms:

3.3 mg/kg soil dw

Additional information

Dihexyl ether exposure did not result in inhibitory effects to nitrate rate formation in an OECD 216. Statistically significant stimulatory effects were observed at the two highest concentrations of 81 and 243 mg/kg.