Herbicides and nitrates in groundwater of Maryland and childhood cancers: A geographic information systems approach

• Main Author: Thorpe, Nancy Mae
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2002
• Subjects: Environmental science; Groundwater; Herbicides; Public health
• ISBN: 0493987894; 9780493987897

Changes in environmental factors may play a role in the etiology of cancer, particularly the increased use of agricultural and household pesticides. This hypothesis-generating study explores spatial patterns of various childhood cancers and herbicide and nitrate concentrations in groundwater supplies throughout Maryland, and investigates potential associations between them. Childhood cancer data were obtained from the Maryland Cancer Registry (MCR) for four cancer types; bone, brain, leukemia, and lymphoma; in children ages 0–17 during the years 1992–1998. SaTScan software (SaTScan 1998), which works within the Geographic Information Systems (GIS) environment of ArcView software (ESRI 1999), performed cancer cluster analysis and calculated relative risk (RR). Higher relative risk areas and potential clusters appeared in several counties within the Piedmont and Coastal Plain Provinces, which include Anne Arundel, Carroll, Cecil, Frederick, Harford, Kent, Queen Anne's, Washington, and Worcester. The water quality data obtained from the U.S. Geological Survey (USGS) and the Maryland Department of the Environment (MDE) included detectable concentrations of the four herbicides, atrazine, simazine, alachlor, and metolachlor, which were investigated in this study along with nitrates. Well-sites were mapped and detectable concentrations noted by placing a two-mile buffer zone around the wells, indicating areas at risk of contamination. The majority of these areas lie within the Piedmont and Coastal Plain Provinces. ArcWofE software (Kemp 1999), a weights of evidence statistical analysis, was employed to determine influencing factors of these compounds leaching into groundwater. Soil and bedrock types were the main factors. Contingency table analysis indicated potential associations with several herbicides. Overall cancer rates for the four types had an Odds Ratio OR = 1.93 (1.18–3.18) with exposure to atrazine, and an OR = 1.54 (1.14–2.07) for metolachlor. Mixtures of three compounds gave an OR = 7.56 (4.16–13.73), indicating a possible synergistic effect. A potential association was indicated between leukemia and nitrates, OR = 1.81 (1.35–2.42), and bone cancer with metolachlor, OR = 2.26 (0.97–5.24). Exposures to the four herbicides were below the maximum contaminant levels. These results gave insight to generate a hypothesis of the potential association between chronic, low-level exposure to these herbicides and nitrates and specific types of childhood cancer.