Pesticide Residues in the Home—Imidacloprid Pre-Publication Executive Summary

The use of spot-on pet parasiticides has risen substantially. Imidacloprid, a commonly used active ingredient (AI), was removed from outdoor agricultural use in 2018 due to evidenced environmental risks. Imidacloprid is an AI in certain spot-on pet parasiticides and, with its metabolites, is now a domestic contaminant. We report two studies of dust and surface contamination in >50 homes in London, UK. In study 1, a time series pre-and-post spot-on application, imidacloprid rapidly contaminates the home at concentrations far exceeding the environmental quality standards that exist. Seven days post-application, imidacloprid concentration in domestic mop water exceeded the acute toxicity maximum acceptable concentration (MAC) by 600-fold and rinsate from fabric on which animals frequently sat was almost 5000-fold the MAC. In study 2, of dust in 50 homes, the 10 homes without resident pets had the lowest imidacloprid concentration. Homes using spot-ons had much higher concentrations (38+/-17 µg/g), comparable to days 5-7 in Study 1. The imidacloprid acceptable daily intake (ADI) for humans applies to the gastric route (residues in food). Multiple routes of human contamination exist; transdermal and inhalation have no standards. There is evidence that imidacloprid is associated with cardiac, neurological and endocrine disruption in mammals, including humans. A precautionary approach is advisable, with responsive use rather than prophylactic use which maintains high levels of domestic contamination.