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Toxicity to soil microorganisms

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Description of key information

Key study: BBA Part VI, 1-1, SETAC, No significant effects on respiration or nitrification, Grade 1997.

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Additional information

The toxicity of the test material to soil microorganisms was determined in a soil respiration and nitrification study performed to GLP and in line with the standardised guidelines BBA Part VI, 1-1 and SETAC. The microbial biomass of the soil -loamy sand -Collombey- was determined prior to application of the test material by measuring substrate-induced respiration to confirm adequate microbial activity. On the basis of this biomass determination, the possible effects of the test material on soil respiration were evaluated after the addition of 1000 mg glucose/100 g dry soil equivalents during the constant initial respiration phase i.e. 1 to 6 hours after glucose amendment. Nitrogen conversion were determined by measuring the content of NH4-N, NO3-N and NO2-N. All post-application measurements were performed in Lucerne amended soil, calibrated with the reference substance dinoseb and related to untreated control. The test material was applied to the soil as acetone solution. The initial nominal test concentrations in soil were 0.67 and 1.67 mg test material per kg soil dry weight corresponding to approximately two- and five-fold the proposed field application rate (i.e. 500 and 1250 g a.i./ha).

Non significant test material induced effects on soil short-term respiration rates were observed. Short-term respiration rates recorded during the constant initial respiration phase in soil treated with two- and five-fold the maximum proposed field application rate deviate by <6 and <5% over the whole period from the untreated control, respectively. In the loamy sand, total-N concentrations at the end of the incubation period, i.e. after 28 days, deviated by <17% and <9% from the control at two- and five-fold application rate, respectively. These figures indicate that the test material has no long lasting effects on N-mineralisation.

It can be concluded that the incorporation of the test material in the tested soil showed no effect on short-term respiration rates with the two-fold application rate. Even when applied with the five-fold application rate, the test material showed no effects. N-mineralisation was not affected in the loamy sand. Therefore, it can be concluded that the test material showed no long lasting effects on N-mineralisation of the tested agricultural soil. No adverse effect of the test material on organic matter turnover, and hence on soil fertility, is to be expected from its use.

The study was performed to a high standard, in line with GLP and standardised guidelines. Accordingly the study has been assigned a reliability score of 1 in line with the principles for assessing data quality set out in Klimisch (1997). The available data are deemed to be relevant, reliable and adequate for the purposes of risk assessment.