NCI’s Ward Retires

Dr. Mary Ward

Dr. Mary H. Ward, senior investigator in the Occupational and Environmental Epidemiology Branch (OEEB) of the National Cancer Institute, retired after 30 years of federal service. Ward is an internationally recognized expert in the study of environmental causes of cancer.  

Throughout her career, Ward made important contributions to our understanding of the potential carcinogenic effects of drinking water contaminants, pesticides and persistent pollutants (POPs) in relation to the etiology of childhood leukemia, gastrointestinal cancers, thyroid and other cancers. Her foundational work established the use of geographic information systems (GIS) for exposure assessment of environmental contaminants, a method widely used today. Her research on nitrates in drinking water had important national policy implications under Environmental Protection Agency’s (EPA) Safe Drinking Water Act. 

Nitrate Ingestion and Cancer Risk 

Ward conducted some of the first case-control and cohort studies of nitrate ingestion and cancer risk with individual-level exposure assessment and evaluation of co-factors that affect N-nitroso compound (NOC) formation. Most NOCs are potent carcinogens in animals, causing tumors at multiple cancer sites. She linked large historical databases of measurements from public water supply to residence histories and found increased risk of bladder, kidney, colorectal, stomach, thyroid and ovarian cancers at nitrate concentrations below the EPA maximum contaminant level.  

There were no databases of nitrate and nitrite levels in foods at the time Ward initiated her research in this area. To address this need, she developed databases of dietary nitrate and nitrite for food frequency questionnaires, which have been a resource for many investigators.  

Ward also led interdisciplinary teams of hydrogeologists and statisticians to develop predictive models that were applied to the cohort’s residence locations to estimate nitrate concentrations from unregulated private wells, which provided drinking water to 70% of the cohort. Together with monitoring data for public water supplies, they were able to estimate long-term average and peak exposure to inform risk analysis. 

Pesticides and Other Contaminants 

With extramural colleagues, Ward developed methods for using remote sensing data and a GIS to estimate indirect exposure to pesticides in the general population. Later, she and colleagues validated this approach with environmental samples in Iowa and California and in Denmark where they found increased risk of childhood leukemia among offspring of mothers with higher density of agricultural crop fields near their homes during their pregnancies. 

Scientific Leadership and Mentoring 

Ward has served the scientific community as part of several important efforts. She chaired the epidemiology review committee of the International Agency for Research on Cancer Monographs Programme on ingested nitrate and nitrite. She served on the National Academy of Sciences Reactive Nitrogen RCN Steering Committee, an interdisciplinary committee whose goal was to assess the ecological and health impacts of humans’ disruption of the nitrogen cycle, and on the President’s Cancer Panel on Environmental Factors in Cancer as an expert on cancer risk related to nitrate contamination of drinking water.

Ward has served on the Steering Committee for the International Childhood Cancer Cohort Consortium since 2019, and as a liaison to the American Academy of Pediatrics Council on Environmental Health and Climate Change since 2015. 

Ward received an M.S. in ecology from the University of Tennessee, Knoxville, and a Ph.D. in epidemiology from The Johns Hopkins University School of Hygiene and Public Health. She has mentored more than 20 post- and pre-doctoral fellows as well as more than 15 master’s and undergraduate students. Her role in mentoring and developing junior scientists has been invaluable in establishing the next generation of scientists to carry on critical work in environmental exposures and cancer.