Considerations regarding a permitted daily exposure calculation for ethyl methanesulfonate

Specification of human exposure limits to compounds with toxicities based on modes of action that allow considerations of a threshold and the safe estimation of a no-observed-effect level (NOEL) is normally based on acceptable daily intake (ADI) or permitted daily exposure (PDE) calculations using appropriate safety factors to account for differences between species, populations, length of observation and severity of lesions. In view of the reliable experimental evidence for a thresholded dose response of the genotoxicity of ethyl methanesulfonate (EMS) as reported in this special issue of Toxicology Letters such an acceptable daily intake proposal is made using the approach for setting permitted daily exposure limits outlined in appendix 3 of the ICH Q3C consensus guideline on residual solvents in pharmaceuticals (ICH, 2005). Up to now the specification of EMS exposure limits was based on the generic threshold of toxicological concern (TTC)-derived limit of 1.5mug/person/day as advocated by the CHMP [CHMP, 2006. Guideline on the limits of genotoxic impurities. www.emea.europa.eu/pdfs/human/swp/519902en.pdf (June 28, 2006) with Q&A www.emea.europa.eu/pdfs/human/swp/43199407en.pdf (June 25, 2008)] or on as low as technically achievable criteria. Such limits have been based on conservative linear dose-effect extrapolations corresponding to an excess cancer risk of 1 in 100,000. We now present an EMS-specific PDE based on the reliable demonstration of a NOEL for induction of mutations in vivo of 25mg/kg/day. Using the most conservative safety factors described in ICH Q3C we derive a PDE of approximately 100 microg/person/day using product safety factors still amounting to 12,000.