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Ecotoxicological information

Toxicity to soil microorganisms

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Description of key information

No adequate data for risk assessment under REACH is available.

Key value for chemical safety assessment

Additional information

The only available study on microorganism toxicity (Cameron, 1993) investigated the effects of benoxacor upon the rate of short-term respiration and on the nitrification and nitrogen-mineralisation capacity of soil micro-organisms under aerobic conditions on two soil types. The study followed the BBA Part VI, 1-1 guideline, was GLP compliant and is considered to be reliable without restriction (Klimisch 1). After 28 days incubation, the rates of short-term respiration and concentrations of ammonium, nitrite and nitrate in treated soil (both rates) deviated from untreated soils by less than 15%. Therefore, the maximum concentration tested (0.45 mg/kg soil dw) was identified as the NOEC for soil microorganisms.

Two agricultural soils, a sandy loam soil and a silty clay loam soil were incubated with benoxacor at concentrations of 0.09 mg a.i. /kg and 0.45 mg a.i. /kg corresponding to an average recommended field rate of 66.6 g/ha and to a fivefold rate, respectively.

A NOEC from a 28 day test is considered a long-term result for microbial populations. However, since only two concentrations were tested and the maximum concentration tested was not higher than 0.45 mg/kg soil dw, only very limited information about the concentration-response relationship is available. This is the recommended approach for agrochemicals according to the OECD TGs 216 and 217.

However, for a chemical substance (i.e. for use in non-agrochemical risk assessments) the test guidelines (e.g. OECD 216 & 217) require that a geometric series of at least five concentrations is used, where the concentrations tested should cover the range needed to determine the ECx values. Consequently, the results of this study, although they are reliable and relevant, are not considered adequate for the purpose of risk assessment under REACH because no EC50 values have been derived.