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Ecotoxicological information

Toxicity to soil microorganisms

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Nitrogen transformation and carbon mineralisation in soil treated with MON 69447 (containing 28 g/L MON 13900) at a rate equivalent to twice the maximum annual application rate (5L/ha) were not statistically different from the control soil, the deviations in measured activity at the end of the study period being less than 25% for all parameters examined.

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A study was performed to determine the effects of MON 69447 (containing acetochlor at 840 g/L and MON 13900 at 28 g/L) on nitrogen transformation and carbon mineralisation by soil microflora according to the SETAC - Europe (1995) guideline “Procedure for assessing the environmental fate and ecotoxicity of pesticides”. The substance was tested at a single rate equivalent to twice the maximum annual application rate (5 L/hectare). The test soil was a common sandy agricultural soil (sandy loam). The microbial biomass of the test soil was measured to be 1.53% of the soil organic carbon. Three experimental groups were created from a single batch of soil. Group 1 consisted of soil and water (added to attain 40% water holding capacity - WHC). Group 2 consisted of soil, lucerne meal (added as a nitrogen source) and water (to attain 40% WHC). Group 3 consisted of soil, lucerne meal and water (to attain 40% WHC) containing test substance. To determine nitrogen transformation, triplicate portions of treated soil and non-treated control soils, placed in glass containers, were sampled after approximately 3 h (Day 0) and 14 d and 28 d of incubation and transferred into deep-freeze storage prior to extraction and analysis for ammonium, nitrite and nitrate ion concentrations using a continuous flow calorimetric autoanalyser. To determine carbon mineralisation, triplicate portions of treated soil and non-treated control soils were placed into respirometer flasks and continuously monitored for carbon dioxide production. After approximately 3 h (Day 0) and 2, 7, 14, 21 and 28 d of incubation the sodium hydroxide respirometer trap fluid was removed for analysis by auto-titration. The metabolic activity of the soil microbial biomass, expressed in terms of carbon mineralisation, was determined from the cumulative production of carbon as carbon dioxide. The reference substance, dinoseb acetate exerted significant disruption of all measured nitrogen transformation and carbon mineralisation activities. Under the study condition, nitrogen transformation and carbon mineralisation in soil treated with test substance at a rate equivalent to twice the maximum annual application rate were not statistically different from the control soil, the deviations in measured activity at the end of the study period being less than 25% for all parameters examined.