Evaluation of the genotoxic potential of dietary metabolites to support the renewal of an active substance under European Commission Regulation (EC) 1107/2009 — fludioxonil case study

The evaluation of the genotoxic potential of dietary metabolites of active substances is an important aspect for the (re)registration of pesticides within the European Union. This paper presents a case study evaluating the genotoxic potential of three dietary metabolites (CGA335892, SYN518580 and CGA227731) of the active substance fludioxonil under Regulation (EC)1107/2009. This tiered process started with (Q)SAR and read across, to enable a ″grouping″ approach, the three metabolites were identified as ″exemplar compounds″ and evaluated for gene mutation, clastogenicity and aneugenicity. Bacterial reverse mutation tests (S. typhimurium. and E. coli strains) were conducted on CGA335892 (negative), SYN518580 (negative) and CGA227731 (positive; TA1537 ± S9; 500-1500 μg/plate). In vitro micronucleus assays in TK6 cells on CGA335892 and SYN518580 were positive at ≤7 and ≤25 μg/mL respectively whereas CGA227731 was clearly negative in human lymphocytes. In vivo genotoxicity assays were conducted to follow up the positive in vitro findings. Mouse micronucleus studies (CGA335892, SYN518580) were negative up to the maximum tolerated / limit dose respectively; CGA335892 and SYN518580 were concluded to be not clastogenic and not aneugenic in vivo. CGA227731 was negative in a rat Comet assay (liver, duodenum); however, following regulatory review a transgenic rodent gene mutation assay was conducted (BigBlue® rats, up to limit dose) to investigate the in vivo mutagenicity of this metabolite. This study was negative (liver, duodenum, bone marrow); CGA227731 is concluded to be non-mutagenic in vivo. Based on this extensive battery of genotoxicity tests, CGA335892, SYN518580 and CGA227731 are concluded to be of no genotoxic concern.