John Wiley & Sons, Ltd.

Surface water mineralization of isopyrazam, according to OECD309: Observations on implementation of the new data requirement within agrochemical regulation

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Surface water mineralization studies (to guideline OECD309) are a new requirement in EU agrochemical regulation and, therefore, industry has little experience with this test. The guideline allows for a number of options within the test design, notably the options to conduct the study under diffuse light and to include an inoculum of suspended sediment. The current study was designed to investigate the potential impact of these options on the degradation rate of a representative compound. The fungicide, isopyrazam, was chosen as it was previously shown to be susceptible to metabolism by phototrophic organisms under a fluorescent light‐dark cycle. The impact of diffuse light was investigated at light intensities representative of those at depth in large, open water bodies (<7% of the incident intensity) and it was demonstrated that metabolism of isopyrazam by phototrophic microorganisms was rapid (DT50 <50 days), whereas degradation in continuous darkness was negligible. Furthermore, investigation at two different light intensities resulted in similar degradation rates, indicating that this transformation mechanism was not proportional to light intensity, provided that there was sufficient light for photosynthesis to occur. Inclusion of suspended sediment did not have a significant impact on the degradation rate of isopyrazam, except at extremely high sediment concentrations, which were not considered representative of conditions in large, open water bodies. Environ Toxicol Chem 2013;9999:XX–XX. © 2013 SETAC

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