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Ecotoxicological information

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:
05/11/1999 - 07/07/2000
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP, Guideline study
Qualifier:
according to
Guideline:
other: SETAC-Europe: Procedures for assessing the environmental fate and ecotoxicity of pesticides, March 1995
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
BBA Part VI, 1-1
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
EPA OPPTS 850.5100 (Soil Microbial Community Toxicity Test)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
no
Details on sampling:
0 – 3 hours, 14 days, 28 days after treatment.
Vehicle:
yes
Details on preparation and application of test substrate:
Application procedure: The test item was applied in 1 mL purified water
Carrier: The reference item was applied using fortified quartz sand (1.5 g per 150 g soil sample)
Test organisms (inoculum):
soil
Total exposure duration:
28 d
Test temperature:
Incubation temperature: 20 ± 2 °C
Moisture:
40 % MWC
Details on test conditions:
See Table 1 for microbial sample / inoculum information
Nominal and measured concentrations:
Initial concentration of test substance:
Low dose: 300 g a.i./ha (corresponding to 2.0 mg MTI446 20 % SG/kg dry soil
High dose: 3.0 kg a.i./ha (corresponding to 20 mg MTI-446 20% SG/kg dry soil)
Reference substance (positive control):
yes
Remarks:
Dinoseb acetate
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
respiration rate
Remarks:
and nitrification rate
Key result
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
respiration rate
Remarks:
and nitrification rate
Details on results:
The maximum rate of initial CO2 evolution from 100 g dry soil equivalent was 0.295 mL/h for soil Speyer 2.3. The microbial biomass expressed as microbial carbon per 100 grams of dry weight soil was calculated to be 12.3 mg microbial carbon.

The pH value of 7.2 was measured for the control soil without lucerne meal at day 0. The corresponding pH with lucerne meal was 7.1. During incubation the pH ranged from 6.9 – 7.2 for the lucerne-free and lucerne-containing samples. Thus, no significant pH changes in lucerne-free soil and a slight increase in lucerne-containing soil took place during the incubation.

No significant influence of MTI-446 20 % SG on soil microbial respiration in soil Speyer 2.3 was observed.

According to Malkomes scheme, rates up to ten times the maximum field rate of MTI-446 20% SG in soil Speyer 2.3 results in negligible effects on soil respiration. Dinoseb acetate results in tolerable effects on soil respiration, but with time the effect on microorganisms is increasing.

For ammonification, there was no deviation between untreated and treated soil samples and values were constant at 0.02 mg per 100 g dry soil. The dinoseb acetate treated soil samples were significantly different from the controls on day 0 and 14, but identical on day 28.

For nitrification, the treatment with MTI-446 20 % SG had no influence on the nitrite formation and transformation.

Mean nitrate levels increased in all samples. The calculated deviation to the control showed only little effects after 28 days of incubation.

Results for the inorganic nitrogen level confirmed that MTI-446 20 % SG had no adverse effect on the nitrification. The soil treated with dinoseb acetate showed a high effect on total inorganic nitrogen.

In the Malkomes scheme the results for MTI-446 20 % SG range in the area of a negligible effect. The results for dinoseb acetate range after 28 days in the area of a tolerable effect.
Results with reference substance (positive control):
See details on results above.
Reported statistics and error estimates:
• The Dixon-test as reported by Sachs (1984) or Dixon (1953) was used to eliminate outliers in the respiration and nitrification experiments.
• In the respiration and nitrification experiments, the mean of individual values at the end of their respective incubation period were statistically evaluated by Dunett's t-test (two-tailed, 5%) to find significant differences between the control and treated samples.
• For the calculation of the microbial biomass the initial and constant CO2 production rate per 100 g of dry soil (VCO2) and Anderson and Domsch (1978) equation were used.
Validity criteria fulfilled:
yes
Conclusions:
Dinotefuran did not cause adverse effects on organic matter turnover, and hence on soil fertility at rates up to ten times the recommended field rate i.e.4 mg a.i./kg dry soil (equivalent to 20 mg MTI-44620% SG/kg).

The reference item dinoseb acetate had a significant effect on the microflora demonstrating the sensitivity of the test system and validity of the experimental design.

Description of key information

Dinotefuran did not cause adverse effects on organic matter turnover, and hence on soil fertility at rates up to ten times the recommended field rate i.e.4 mg a.i./kg dry soil

Key value for chemical safety assessment

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

Additional information