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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:
16th November 2000 to 8th August 2001
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
Qualifier:
according to guideline
Guideline:
OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
See 'Any other information on materials and methods incl. tables' below.
Vehicle:
no
Details on preparation and application of test substrate:
AMENDMENT OF SOIL
- Type of organic substrate: 0.5 % w/w lucerne meal for nitrification test.

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method: each soil sample was laid out as a thin layer of approximately 2.5 cm thickness and 12 mL of the appropriate treatment solution added dropwise. The soil was mixed thoroughly. Control samples were prepared by applying distilled water to the soil in the same manner as the test material.
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
20 ± 2 ºC
Details on test conditions:
TEST SYSTEM
- No. of replicates per concentration: 3
- No. of replicates per control: 3

SOIL INCUBATION
- Method: soil samples corresponding to approximately 1.2 kg soil (oven dry equivalent) at approximatelt 40 % MWHC were weighed into 2.5 L plastic containers. Containers were incubated in the dark at 20 ± 2 ºC for 6 days.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- History of site: no pesticide or fertiliser treatment for at least 5 years before collection.
- Vegetation cover: surface vegetation removed
- Treatments with pesticides or fertilizers: not for at least five years
- Depth of sampling: top soil immediately below surface vegetation
- Soil taxonomic classification: sandy loam soil
- pH (in water): 6.5
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight): 1526
- Maximum water holding capacity (in % dry weight): 47.6 % (adjusted to approximately 40 % before use)
- Cation exchange capacity: 9.6 mEq/100 g
- Pretreatment of soil: passed through 2 mm sieve to remove particles larger than coarse sand
- Storage (condition, duration): approximatelt 4 ºC until use

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- 0-3 h and 7, 14 and 28 days for determination of soil respiration activity and nitrate.

VEHICLE CONTROL PERFORMED: no
Nominal and measured concentrations:
0, 1.28 and 6.4 kg a.s./ha
Reference substance (positive control):
yes
Remarks:
dinoseb acetate
Key result
Duration:
28 d
Remarks on result:
other: Soil respiration or nitrogen transformation not affected
Details on results:
The determination of microbial biomass by respiration in glucose-amended soil gave a calculated biomass of 263.6 mg C/kg oven dry soil. In soil treated with 1.28 and 6.4 kg a.s./ha, respiration in glucose-amended soil did not deviate from control respiration by more than the established tolerance level of 25 %. At 28 days post-application, mean respiration rates in soils treated with 1.28 and 6.4 kg a.s./ha deviated from control rates by 0.2 and 11.5 %, respectively. There were no statistically significant differences between control and treated soil respiration rates. Levels of nitrate in untreated soils increased from 10.5 mg N/kg oven dry soil at 0-3 hours to 13.1, 38.3 and 53.2 mg N/kg oven dry soil at 7, 14 and 28 days, respectively. Levels in both 1.28 and 6.4 kg a.s./ha treated soils did not deviate from control levels by more than the threshold tolerance at 25 %. Results for both treatment rates did not reach statistical significance at 14 days but not at 0-3 hours, 7 days or 28 days.
Results with reference substance (positive control):
The reference substance caused statistically significant reductions in respiration and nitrification that deviated from the control levels by >25%.
Reported statistics and error estimates:
Results of glucose-amended soil and concentrations of nitrate in soil were subjected to analysis of variance. Pairwise comparisons between the treated groups and the control were performed using Dunnett's t-test. Data from each of the sampling times were analysed separately. All statistical tests were two-tailed.
Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of the test, Omite 570 EW will have no effect on soil microflora respiration or nitrification under field conditions on the basis that respiration rates and nitrate levels in soil treated with the test material did not deviate from control respiration and nitrate levels by more than the established tolerance level of 25 %.
Executive summary:

The objective of the study was to investigate the effects of Omite 570 EW (570 g/L EW formulation of propargite) on the rate of short-term respiration and nitrogen transformation of soil microflora under aerobic conditions. The test material was incorporated into sandy loam soil at 1.28 and 6.4 kg a.s./ha (equivalent to 1.707 and 8.535 mg a.s/kg dry soil).

Throughout the test and at the end of the test (28 days post-application), rates of short-term microbial respiration in treated soil deviated from those of untreated soil by <25 %. The incorporation of the test material at the tested application rates had no impact on short-term microbial respiration. Throughout the test and at the end of the test (28 days post-application), concentrations of nitrate in treated soil deviated from those in untreated controls by <25 %. The incorporation of the test material at the tested application rates had no impact on soil nitrogen transformation.

The results showed that the incorporation of Omite 570 EW at 1.28 and 6.4 kg a.s./ha did not affect soil respiration or nitrogen transformation.

Description of key information

No effect on soil microflora respiration or nitrification under field conditions; study conducted in accordance with OECD Guideline 216 and 217; Chapelo, 2002

Key value for chemical safety assessment

Additional information

The objective of the study was to investigate the effects of Omite 570EW (570 g/L EW formulation of propargite) on the rate of short-term respiration and nitrogen transformation of soil microflora under aerobic conditions. The test material was incorporated into sandy loam soil at 1.28 and 6.4 kg a.s./ha (equivalent to 1.707 and 8.535 mg a.s/kg dry soil). Throughout the test and at the end of the test (28 days post-application), rates of short-term microbial respiration and concentrations of nitrate in treated soil deviated from those of untreated soil by <25 %. The incorporation of the test material at the tested application rates had no impact on short-term microbial respiration and soil nitrogen transformation. The results showed that the incorporation of Omite 570 EW at 1.28 and 6.4 kg a.s./ha did not affect soil respiration or nitrogen transformation.

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