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Toxicity to soil microorganisms

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Description of key information

NOEC (28 d) = 300 mg/kg dw (nominal, nitrogen transformation)
EC50 (28 d) = 633.5 mg/kg dw (nominal, nitrogen transformation)

Key value for chemical safety assessment

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

Additional information

To investigate the effects of OPP (CAS-No. 90-43-7) on soil respiration and nitrification of soil micro-organisms, two GLP study are available. In the first test the activity of soil microflora was investigated with regard to nitrogen transformation (mineralization) over a period of 100 days of exposure. This test was performed according to OECD Guideline No. 216 (Schulz 2012). A loamy soil enriched with Lucerne meal (concentration in soil 0.5%) was used.The test consisted of 10 treatment groups (including control) with three replicates each. Test item concentrations were the following: 1, 5, 10, 30, 60, 100, 300, and 1000 mg test item per kg soil dry weight. Nitrogen transformation (ammonium, nitrate and nitrite) was determined on day 0 (after approx. 3 hours) and at intervals of 14, 28 and 100 days after application.

The NOEC of OPP was calculated to be 300 mg/kg soil dry weight 28 days and 100 days after application. The EC50 was calculated to be 633.5 mg/kg and 829.1 mg/kg soil dry weight 28 days and 100 days after application, respectively.

The second test was performed according to OECD Guidelines No. 216 and 217 (Reis 2007). A loamy sand soil was tested and the test concentrations were 0.1 mg a.i./kg soil and 1.0 mg a.i./kg soil. The carbon transformation in soil after addition of glucose was measured by determining the CO2-production over a period of up to 24 hours at day 0, 7, 14 and 28 after treatment. For the nitrogen-transformation in soil enriched with lucerne meal (concentration in soil 0.5%), NH4-, NO2- and NO3-nitrogen concentrations were determined on day 0, 7, 14 and 28 after treatment. OPP has no impact on respiration and nitrogen transformation of soil microflora when applied up to 1.0 mg a.i./kg soil.