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Toxicity to soil microorganisms

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Description of key information

No adverse effects of the test item on carbon transformation could be observed at all test item concentrations tested after 28 days. Therfore the NOEC was estimated to be > 0.2 mg a.s./100 g dry weight, which corresponds to > 2 mg a.s./kg dw.
No adverse effects of the test item on nitrogen transformation could be observed at all test item concentrations tested after 56 days. Therfore the NOEC was estimated to be > 0.2 mg a.s./100 g dry weight, which corresponds to > 2 mg a.s./kg dw.

Key value for chemical safety assessment

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

Additional information

A carbon transformation study and a nitrogen transformation study with the test item was performed in one study according to BBA IV, part 1-1. are available and presented below.


The presented study was peer-reviewed during the assessment of teflubenzuron according to Council Directive 91/414/EEC.


 


Key information


Celamerck (1985): Testing of the influence of CME 134 on the microflora of the soil. Unpublished report, report No. 134AA-924-002, according to Draft Assessment Report (2007) according to Council Directive 91/414/EEC, crossreference: MCA 8.5.1/01


In a soil microbial activity study according to BBA IV, part 1-1 (1981), the effects of the test item on the carbon and nitrogen transformation were investigated in tow differents soils (Ingelheim sand and Schwabenheim loam). In comparison to actual guidelines (in particular OECD 216/217) the requirements at the time at which this study was performed have only been changed slightly (e.g. no reference substance is needed any more; the pre-treatment is different: formerly air-dried and re-wetted – today field fresh). The study is considered to be scientifically valid.


The test item was applied to samples of the soil at application rates of 0.02 and 0.2 mg a.s./100 g soil dry weight (dw). Test item treated soils and control soil treatments were incubated at 21 °C in the dark for 28 days.


Carbon transformation:


For the application of the test and reference substance the soil samples were spread on a plate. The respective amounts of the test item were dissolved in 1 mL acetone and evenly distributed on the soil. After evaporation of the solvent, the samples were mixed and adjusted to 50% (soil 1) and 46% (soil 2) of the maximum water holding capacity with demineralised water.


The treated soil samples were transferred into brown aerated glass bottles (250 mL). The air was led into a gas jar, containing 40 mL 1 M NaOH solution. The CO2 in the air was adsorbed by a 10% NaOH solution and was washed in water without carbonic acid. The flow rate was 5 mL/min and the temperature was 21±1°C. Samples were taken at days 0, 1, 2, 4, 7, 14, 21 and 28.


The CO2 was determined by means of titration with 0.05 M H2SO4, using a pH glass electrode and a Metrohm titrator. The blank reading determined at titration of the NaOH solution was subtracted.


Nitrification transformation:


For the application of the test substance 500 g of the soil were spread on a plate and the active substance, ammonium sulphate and horn farina were added in the corresponding amounts. After mixing, the soils were adjusted to 40% of the maximum water holding capacity. In each treatment sampling was repeated twice, amounts taken being 40 g d.w. The soil samples were weighed into 500 mL wide-mouth bottles, which then were tightly closed. The samples were incubated at 21±1°C. Samples were taken at days 0, 7, 14, 28 and 56. The samples were extracted by shaking with an aqueous solution of aluminium sulphate (Al2(SO4)3*10 H2O). The nitrate nitrogen was determined with a NO3-specific electrode against an Ag/AgCl reference electrode using a calibration series of potassium nitrate solutions. The ammonium nitrogen was determined by means of a selective electrode. The evaluation was carried out using a cali­bration series of ammonium chloride solutions.


The results show that the test item did not exert any influence on the soil respiration, since the values obtained for the treated soil samples did not reveal differences against the corresponding controls. Generally, the respiration rates in the samples incubated under addition of lucerne were essentially higher than the respiration of the soil samples to which no lucerne has been added. In the tests concerning nitrification of ammonium sulphate only in the sandy soil a slight inhibitory effect was seen, which led to an initial retardation but did not have any lasting influence on the nitrogen metabolism. The mineralisation of organic substrate (horn farina) was not influenced by addition of various amounts of the test item (up to 2 mg a.s./kg).


Conclusion


No adverse effects of the test item on carbon nor on nitrogen transformation could be observed at all test item concentrations tested after 28 days. Therfore the NOEC was for both endpoints estimated to be > 0.2 mg a.s./100 g dry weight, which corresponds to > 2 mg a.s./kg dw.