Using residential history and groundwater modeling to examine drinking water exposure and breast cancer

Abstract

Background: Spatial analyses of case-control data have suggested a possible link between breast cancer and groundwater plumes in upper Cape Cod, Massachusetts.

Objective: We integrated residential histories, public water distribution systems, and groundwater modeling within geographic information systems (GIS) to examine the association between exposure to drinking water that has been contaminated by wastewater effluent and breast cancer.

Methods: Exposure was assessed from 1947 to 1993 for 638 breast cancer cases who were diagnosed from 1983 to 1993 and 842 controls; we took into account residential mobility and drinking water source. To estimate the historical impact of effluent on drinking water wells, we modified a modular three-dimensional finite-difference groundwater model (MODFLOW) from the U.S. Geological Survey. The analyses included latency and exposure duration.

Results: Wastewater effluent impacted the drinking water wells of study participants as early as 1966. For > 0-5 years of exposure (versus no exposure), associations were generally null. Adjusted odds ratios (AORs) for > 10 years of exposure were slightly increased, assuming latency periods of 0 or 10 years [AOR = 1.3; 95% confidence interval (CI), 0.9-1.9 and AOR = 1.6; 95% CI, 0.8-3.2, respectively]. Statistically significant associations were estimated for ever-exposed versus never-exposed women when a 20-year latency period was assumed (AOR = 1.9; 95% CI, 1.0-3.4). A sensitivity analysis that classified exposures assuming lower well-pumping rates showed similar results.

Conclusion: We investigated the hypothesis generated by earlier spatial analyses that exposure to drinking water contaminated by wastewater effluent may be associated with breast cancer. Using a detailed exposure assessment, we found an association with breast cancer that increased with longer latency and greater exposure duration.

Figure 1

Study area in the Cape Cod region of Massachusetts. The upper region of Cape Cod consists of five towns: Barnstable, Bourne, Falmouth, Mashpee, and Sandwich. Groundwater contamination was suspected in several areas, but the BWPCF was the only source with the potential to impact drinking water in this study population.

Figure 2

BWPCF and public drinking water wells. The map shows the locations of three BWC public drinking water wells in relation to the wastewater facility, suspected groundwater plume, and approximate water district boundary. Private drinking water wells are not shown to maintain confidentiality.

Figure 3

Particle-tracking analysis for groundwater originating at BWPCF. Groundwater containing effluent was determined to have reached the well when a particle track ended in the model grid cell containing the well. If the 1961 Straightway well was pumping at a low rate, groundwater from the BWPCF from start of its operation in 1937 would have reached the Simmons Pond public drinking water well in 1971. At a higher pumping rate, contaminated groundwater would have reached Straightway well in 1966. These 2 years define the start of exposure in analyses for the low and high pumping rates.