We used the C57BL/6 mouse strain for consistency with the studies of Yang et al. (2000, 2001, 2002). C57BL/6J female mice (6–7 weeks of age) were purchased for the initial (recovery) study from the Jackson Laboratories (Bar Harbor, ME). However, during the course of that study, many of the mice had skin lesions. We later learned that C57BL/6J mice have become genetically susceptible to ulcerative dermatitis.Thus, for the dose–response studies, we purchased C57BL/6N female mice (6–7 weeks of age) from Charles River Laboratories (Raleigh, NC). Once at the U.S. EPA’s animal care facilities (accredited by the Association for Assessment and Accreditation of Laboratory Animal Care), animals were housed in groups of eight in polycarbonate cages with hardwood Products, Warrensburg, NY). They were provided a 12-hr light:dark cycle (light, 0600–1800 hours; dark, 1800–0600 hours), maintained at 22.3 ± 1.1°C and 50 ± 10% humidity, and given ad libitum access to both food (5P00 Prolab RMH 3000; PMI Nutrition International, Richmond, IN) and water. Animals were acclimated for at least 10 days before dosing began. All procedures employed in this study were approved in advance by the Institutional Animal Care and Use Committee of the National Health and Environmental Effects Research Laboratory, U.S. EPA; all animals were treated humanely and with regard for alleviation of suffering.