Biography

Dr. Ward received an M.S. in ecology from the University of Tennessee and a Ph.D. in epidemiology from The John Hopkins School of Hygiene and Public Health. Her research focuses on environmental and occupational causes of cancer, with special emphasis on pesticides and nitrates in relation to the etiology of non Hodgkin's lymphoma, childhood leukemia, and gastric cancer. She is examining the etiologic role of nitrosamines and their precursors with respect to drinking water and dietary ingestion for cancers of the brain, bladder, colon, pancreas, stomach, esophagus, and nasopharynx. Dr. Ward is responsible for developmental work using geographic information systems for exposure assessment of environmental contaminants. For this effort, she received a DCEG Intramural Research Award in 1999 and an NIH Merit Award in 2000.

Research Interests

Nitrates, Pesticides and Cancer and Environmental Exposure Assessment

We are using innovative methods such as geographic information systems (GIS) to display and analyze environmental exposure data. Using GIS and remote sensing data, we are participating in interdisciplinary collaborations to develop new methods of exposure assessment for epidemiologic studies of cancer risk in relation to drinking water contaminants and agricultural pesticides.

Nitrates

The endogenous formation of carcinogenic N nitroso compounds can occur following ingestion of nitrate from drinking water. Certain foods are also sources of these agents. Only a limited number of analytic epidemiologic studies have evaluated this exposure issue with respect to diet and drinking water. We conducted a case control study that found a dose response relation between risk of non Hodgkin's lymphoma and prior exposure to elevated nitrate in drinking water. Additional analytic studies are underway to evaluate further the importance of drinking water nitrate in the etiology of lymphoma, leukemia, and cancers of the brain, bladder, colon, kidney, pancreas, stomach, and esophagus

An analysis of dietary intake of volatile N-nitroso compounds and risk of nasopharyngeal cancer (NPC) was the first study of NPC to estimate relative intake levels of these compounds from dietary sources. Higher intakes during early childhood were associated with elevated risk of NPC in adults. An analysis of individual food groups failed to show significant associations with risk, illustrating the importance of considering N-nitroso compound intake across all foods.

To further evaluate the possible role of drinking water nitrate exposure in the development of cancer, we are conducting an ecologic study of cancer incidence in the Platte River Valley of Nebraska and Colorado, an area with some of the highest drinking water nitrate levels in the country. Population exposure via both community water supplies and private wells is being characterized at the block group level. Annual monitoring data is being used to characterize the population exposed to nitrate through community water systems. Through an interdisciplinary collaboration with colleagues in hydrology, engineering and remote sensing, information about land use, fertilizer application rates, the location of livestock feeding operations, soil type, and other factors are being incorporated into a GIS to estimate levels of nitrate in drinking water for the population using private wells.

Pesticides

A feasibility study using remote sensing data and a GIS to estimate indirect exposure to pesticides demonstrated that using available data, accurate historical crop maps could be produced and that these could be linked to pesticide use data to estimate probabilities of indirect exposure to agricultural pesticides. A total of 24% of the study population in an agricultural area were determined to live within 500 meters of crop fields likely to have been treated with pesticides. This was the first study to estimate the prevalence of potential indirect exposure to agricultural pesticides in the general population. Further work in this area by our collaborators included the development of a method to automate crop mapping from satellite imagery. The method was found to be successful at classifying crops into two categories: corn and other crop types, over a 15 county area of Nebraska. We are continuing to refine the GIS-based approach to estimating agricultural pesticide exposure by incorporating information from a pesticide drift model. A validation study is underway in Iowa to compare agricultural pesticide levels in carpet dust samples with several GIS-based exposure metrics including one that incorporates information on wind direction and pesticide drift.

With collaborators in California, we are planning to evaluate agricultural pesticide use near residences as a risk factor for childhood leukemia in an ongoing study. Carpet dust samples will be analyzed for pesticides, and information about the current and historical location of crops near residences will be determined.

Chemicals

Using a GIS, residential proximity to specific industries, hazardous waste sites, and specific chemical releases as reported by the Environmental Protection Agency's Toxic Release Inventory are being evaluated in a recently completed study of non-Hodgkin's lymphoma at four centers. Plans are underway to do a similar type of an analysis in a new bladder cancer study in New England.

Keywords

agricultural exposures, bladder cancer, brain cancer, drinking water contaminants, environmental carcinogens, exposure assessment, geographic information systems, nitrate, N-nitroso compounds, non-Hodgkin's lymphoma, stomach cancer

Selected Publications

• Ward MH, Zahm SH, Blair A. "Pesticides and cancer risk: Clues from epidemiology studies of farmers and the general population." Pesticides People Nature 1999; 1:25-32.
• Ward MH, et al. "Dietary exposure to nitrite and nitrosamines and risk of nasopharyngeal carcinoma in Taiwan." Int J Cancer 2000; 86:603-609.
• Ward MH, et al. "Identifying populations potentially exposed to agricultural pesticides using remote sensing and a geographic information system." Environ Health Perspect 2000; 108:5-12.
• Ward MH, Prince JR, Stewart PA, Zahm SH. "Determining the probability of pesticide exposures among migrant farmworkers: Results from a feasibility study." Am J Indust Med 2991; 40:538-553.

Collaborators

DCEG Collaborators

• Michael Alavanja, Dr.P.H.; Dalsu Baris, M.D., Ph.D.; Erin Bell, Ph.D.; Kenneth P. Cantor, Ph.D.; Joanne Colt, M.P.H.; Anneclaire DeRoos, Ph.D.; Mustafa Dosemeci, Ph.D.; Barry Graubard, Ph.D., Patricia Hartge, Sc.D.; Michael Hauptman, Ph.D.; Wonjin Lee, M.D.; Jay Lubin, Ph.D.; Debra Silverman, Sc.D.; Patricia Stewart, Ph.D.; Shelia Zahm, Sc.D.

Other Scientific Collaborators

• Patricia Buffler, Ph.D., University of California at Berkeley, Berkeley, CA
• David Camann, M.S., Southwest Research Institute, San Antonio, TX
• James Cerhan, M.D., Ph.D., Mayo Clinic, Rochester, MN
• Pierluigi Cocco, M.D., University of Cagliari, Sardinia, Italy
• James Giglierano, M.S., Iowa Department of Natural Resources, Iowa City, IA
• Ahmedin Jemal, Ph.D., D.V.M., American Cancer Society, Atlanta, GA
• Lizbeth Lopez Carrillo, Ph.D., National Institute for Public Health, Mexico City, Mexico
• Susan Maxwell, Ph.D., U.S. Geologic Survey, Sioux Falls, SD
• John Nuckols, Ph.D.; John Reif, D.V.M., Colorado State University, Ft. Collins, CO
• Peggy Reynolds, Ph.D., California Department of Health, Oakland, CA
• Peter Weyer, Ph.D., University of Iowa, Iowa City, IA