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Toxicity to soil microorganisms

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Description of key information

In a reliable guideline compliant study, the activity of the microorganisms transforming nitrogen in the soil was slightly inhibited by the test substance at 50 mg a.i./kg soil dw. The EC50 was 130 mg a.i./kg soil dw. Furthermore C12-16 ADBAC had no long-term influence on nitrogen and carbon transformations in sandy loam and low humic content sandy soils. The same behaviour is expected for C16 TMAC.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:
130 mg/kg soil dw
Long-term EC10 or NOEC for soil microorganisms:
70 mg/kg soil dw

Additional information

A guideline compliant nitrogen transformation test was conducted on the read-across substance C12-16 ADBAC. Analytical determination of the test substance was performed. The concentrations ranged from 0, 50, 100, 200, 400, 800, 1,600, 3,200 and 6,400 mg a.i./kg soil dw. The activity of the microorganisms transforming nitrogen in soil was slightly inhibited at 50 mg a.i./kg soil dw. The EC50 was 130 mg a.i./kg soil. The EC10, EC20 and EC80 were 70, 90 and 200 mg a.i./kg soil dw, respectively. Denitrifying microorganisms were not affected at concentrations ranging from 400 to 3,200 mg a.i./kg soil dw whereas the microorganisms responsible of the formation of nitrate were inhibited at these concentrations. The denitrifying microorganisms were inhibited at 6,400 mg a.i./kg soil dw because after 28 days only a limited amount of the nitrate was removed (van Ginkel CG and van der Togt B, 2004).

The effects of C12-16 ADBAC on carbon mineralization and nitrogen transformation activity of soil micro-organisms in a sandy loam soil and a low humic content sand soil were investigated in a 28 day guideline study. Fifty grams dry weight of soil samples were mixed with lucerne meal and placed in 100 mL bottles. The samples were incubated in the dark at 20±2°C for 28 days. The moisture content of the samples was checked weekly. Samples were treated with test substance at concentrations 0, 10, 100 and 1,000 mg a.i./kg soil dw. No analytical determination of the test substance was performed. CO2 evolution was determined on Days 5 – 8 and 25 – 28. The difference in CO2 production and nitrogen transformation between the treated and untreated soil samples did not exceed 25% after 28 days of incubation. The highest inhibition recorded was 82.5% in the nitrite formation rate at 10 mg a.i./kg soil dw in the sandy loam soil. After 28 days of incubation however, no relevant effect was observed (i.e., less than 25% reduction). Test substance is therefore considered to have a low potential to adversely affect the microbial functions of sandy loam and low humic content sandy soils. The test substance can be characterised as having no long-term influence on nitrogen and carbon transformations in soils (de Vette HQM et al.,2001).