Research contributes to the fields of exposure science, health geography, and environmental epidemiology. His scholarship falls into two lines of inquiry: (1) identifying environmental factors that play important roles in disease morbidity, and (2) developing space-time methods that improve our ability to investigate exposure-disease relationships. Highlights of his work include pioneering development of space-time information systems for lifetime exposure reconstruction, and epidemiology of low-level exposure to arsenic in drinking water. He has published on drinking water contaminants, air pollutants, arsenic, cadmium, asthma, osteoporosis, stroke, and different types of cancers, and enjoys tackling environmental epidemiologic and spatio-temporal methodological problems to advance population health.