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Toxicity to soil microorganisms

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toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Study period:
not reported
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
according to guideline
BBA Part VI, 1-1
Version / remarks:
not specified
GLP compliance:
not specified
Analytical monitoring:
quartz sand
Details on preparation and application of test substrate:
Two different soils were used for the test (a loamy sand and a silt).
The sieved soil (max. 5 kg dry weight) was thoroughly mixed with ground quartz sand (10 g sand/kg dry weight, control) or a mixture of quartz sand and the test material (0.27 or 2.7 mg a.i./kg dry weight of soil) in 20 L stainless steel containers by tumbling on a rotator mixer. After treatment with sand or with sand and the test material the samples were divided into two equal amounts. A part was mixed with pulverized ammonium sulfate (1000 mg/kg) and quartz sand, the second only with quartz sand.
Test organisms (inoculum):
Total exposure duration:
28 d
Test temperature:
20 + 2 °C
40 - 50%
Organic carbon content (% dry weight):
Nitrogen content (% dry weight):
Details on test conditions:
The organic carbon for the second silty soil is 1.23 % and the Nitrogen content is 0.17%.
The soils were obtained from the field, passed through a sieve (2 mm) and stored at 20 + 2 °C for at least 14 but no longer than 28 days. Samples of the thus treated soils corresponding to 50 g dry weight were weighed into brown glass bottles (ground area 6 x 6 cm, height 14 cm). The bottles were closed with air-permeable plastic sheets and kept at 20 + 2 °C in the dark. The soil moisture during the study was equivalent to 40 - 50 % of the water capacity.

Immediately after the treatment and 7, 14, 21 and 28 days later, soil samples (equivalent to 50 g dry weight) were removed. After thorough mixing, portions corresponding to 10 g of dry weight of each sample were weighed and extracted with 50 ml of IN KC1 for 60 min on a mechanical shaker (approx. 200 rpm). The soil extracts were filtered to remove soil particles and analyzed for their content of ammonium, nitrite and nitrate plus nitrite on a Technicon Autoanalyzer II. Soil samples and soil extracts which could not be extracted or analyzed immediately, were stored in the deep-freezer at -20 + 2 °C.
Nominal and measured concentrations:
Nominal: 0.27 mg a.i./kg dry wt.soil (equivalent to 0.2 kg a.i./ha) and 2.7 mg a.i./kg dry wt. soil (equivalent to 2 kg a.i./ha).
Reference substance (positive control):
not specified
Key result
28 d
Dose descriptor:
Effect conc.:
> 2.7 mg/kg soil dw
Nominal / measured:
Conc. based on:
act. ingr.
Basis for effect:
nitrate formation rate
Details on results:
The highest recommended rate of the test material did not show any meaningful influence on N-mineralization in a silt soil.
In the loamy sand soil, both rates caused an insignificant stimulation of the mineralization of native soil nitrogen (5-11% in comparison to the untreated control) which was balanced, however, already on day 28 after treatment.
The nitrification of added ammonium in the loamy sand soil was not influenced by treatment at both rates of test materiial. In the silt soil the formation of nitrate was insignificantly delayed by both rates of the insecticide (2-5% in comparison to the untreated control). Indentical amounts of nitrate were found, however, at the end of the experiment (day 28) in treated and untreated soil samples.

Please refer to "overall remark/ attached background material" field for result tables.

Validity criteria fulfilled:
not specified
The present guideline study was conducted in compliance with GLP. Under the test conditions used, the test material, applied at 0.27 and at 2.7 mg/kg dry wt. soil, had no negative influence on nitrogen transformation or mineralization of added nitrogen in a silt soil and a loamy sand.

Description of key information

The test material, applied at 0.27 and at 2.7 mg/kg dry wt. soil, had no negative influence on nitrogen transformation or mineralization of added nitrogen in a silt soil and a loamy sand.

Key value for chemical safety assessment

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

Additional information

A key study investigating the toxicity of test material to N-cycle of soil microorganisms was available (1988). This test was conducted according to BBA Guideline, Part VI, 1-1 (1987). The test material was incubated in two different soil types (silt and sandy loam) for 28 days at two concentration rates (0.2 and 2 kg a.s./ha equivalent to 0.27 and 2.7 mg a.s./kg dws, respectively). The results found in the treatment groups regarding nitrogen transformation and mineralization did not show any impact of this substance on soil microorganisms after 28 days.


A supportive study according to BBA Guideline, Part VI, 1-1 (1987) was performed on C-cycle with soil microorganisms. For the two tested soils, no impact of test item is expected after 28 days the soil respiration and the microbial mineralization up to 2.67 mg a.s./kg dws.