The arsenic-containing feed additive roxarsone was used for more than 60 years to promote weight gain and to prevent parasitic infections in poultry and swine before its use was halted in Europe and North America because of concerns of exposure to cancer-causing arsenic metabolites. But the additive is still used in Asia. Researchers led by the University of Alberta’s X. Chris Le and Wuhan University’s Bin Hu were interested in identifying and assessing arsenic-containing metabolites that people who eat roxarsone-fed poultry may be exposed to. They conducted a study of 1,600 chickens that ate either standard chicken feed or feed containing roxarsone. The researchers then sampled the birds’ livers for arsenic-containing metabolites. Previously, they reported eight of these metabolites in chickens that consumed roxarsone. Now, they have identified three others, all of which are methylated phenylarsenical metabolites (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201700736). The metabolites were found in chicken livers even five days after roxarsone supplementation had been halted—a typical preslaughter safety window used by the poultry industry for the additive to clear—raising concerns about human exposure to the potentially toxic metabolites if the chicken livers are consumed.