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Toxicity to soil microorganisms

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Description of key information

In a study conducted according to OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test) long-term potential effects of Biofert Plusz on the carbon transformation activity of soil microorganisms was investigated.Overall results support the conclusion that any long-term effects of the test substance on exposed microbial soil organisms are not to be expected (NOEC > 20000 mg/kg dw).

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for soil microorganisms:
20 000 mg/kg soil dw

Additional information

In a study conducted according to OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test) long-term potential effects of Biofert Plusz on the carbon transformation activity of soil microorganisms was investigated. Biofert Plusz was applied to the soil at test substance concentrations of 19.5, 78.1, 313, 1250, 5000 and 20000 mg/kg soil dw nominal. The treated soils were incubated for 28 d at 49.9 -53.8% of the maximum water holding capacity, a pH of 6.34 -6.93 and a temperature of 19 -21°C. The glucose induced respiration was measured on day 0 and after 7, 14, and 28 d. On each occassion, aliquots of the soil were amended with glucose (4000 mg/kg soil). Oxygen consumption was measured over the subsequent 24 h period and compared to that of the untreated control.

Biofert Plusz induced a strong increase of the soil respiration rate throughout the first seven days of exposure at 1250, 5000 and 20000 mg/kg soil dw, presumably due to serving as microbial N-source. After further seven days this induction of microbial respiration was down-regulated, resulting in no statistically significant differences compared to the control at all test substance concentrations. After 14 and 28 days of exposure, substrate induced microbial respiration rate at substance concentrations of 313, 1250, 5000 and 20000 mg/kg soil dw leveled down to the value range measured at day 0. Even the highest applied test substance concentration of 20000 mg/kg dw caused no decrease, but instead a slight increase of the glucose induced respiration rate compared to control at day 28. The decrease seen at TS concentrations of 1250 and 5000 mg/kg dw in the course of exposure may be attributable to prolonged adaptation of exposed microbial communities to differing feed availability, resp. changing C/N ratio. Overall results support the conclusion that any long-term effects of the test substance on exposed microbial soil organisms are not to be expected (NOEC > 20000 mg/kg dw).