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Toxicity to soil microorganisms

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The influence of cloquintocet-mexyl on soil microorganisms was investigated in a 28-day study performed according to the BBA Part VI, 1-1 guideline (Morgenroth, 1992). The study was GLP compliant and is considered to be reliable without restriction. Two agricultural soils, a sand and a silty loam, were used in the experiments. Microbial respiration in both soil types, as measured by CO2 production, was not significantly affected by the test item. In addition, cloquintocet-mexyl showed no significant effects on the nitrification process in both soils. It was concluded that cloquintocet-mexyl (CGA185072) had no significant effects on soil respiration and nitrification at soil concentrations up to 0.27 mg/kg (dry weight) in the soils tested.

A NOEC from a 28 day test can be considered as a long-term result for microbial populations. However this low NOEC is based on the highest concentration tested. The true NOEC is expected to be significantly higher. Only two (low) concentrations were tested and no ECxx value could be derived from this study. Thus, although the study is reliable, it is considered not adequate for the purpose of risk assessment under REACH.

In order to fulfill the Annex IX data requirement an OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test) testing is proposed by Syngenta Ltd (lead registrant). This additional test is only needed in order to fulfill the data requirement but is not needed as a consequence of the chemical safety assessment.

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