Spatial variations in the incidence of breast cancer and potential risks associated with soil dioxin contamination in Midland, Saginaw, and Bay Counties, Michigan, USA

Dajun Dai,Tonny J Oyana

doi:10.1186/1476-069x-7-49

Abstract

BackgroundHigh levels of dioxins in soil and higher-than-average body burdens of dioxins in local residents have been found in the city of Midland and the Tittabawassee River floodplain in Michigan. The objective of this study is threefold: (1) to evaluate dioxin levels in soils; (2) to evaluate the spatial variations in breast cancer incidence in Midland, Saginaw, and Bay Counties in Michigan; (3) to evaluate whether breast cancer rates are spatially associated with the dioxin contamination areas.MethodsWe acquired 532 published soil dioxin data samples collected from 1995 to 2003 and data pertaining to female breast cancer cases (n = 4,604) at ZIP code level in Midland, Saginaw, and Bay Counties for years 1985 through 2002. Descriptive statistics and self-organizing map algorithm were used to evaluate dioxin levels in soils. Geographic information systems techniques, the Kulldorff's spatial and space-time scan statistics, and genetic algorithms were used to explore the variation in the incidence of breast cancer in space and space-time. Odds ratio and their corresponding 95% confidence intervals, with adjustment for age, were used to investigate a spatial association between breast cancer incidence and soil dioxin contamination.ResultsHigh levels of dioxin in soils were observed in the city of Midland and the Tittabawassee River 100-year floodplain. After adjusting for age, we observed high breast cancer incidence rates and detected the presence of spatial clusters in the city of Midland, the confluence area of the Tittabawassee, and Saginaw Rivers. After accounting for spatiotemporal variations, we observed a spatial cluster of breast cancer incidence in Midland between 1985 and 1993. The odds ratio further suggests a statistically significant (α = 0.05) increased breast cancer rate as women get older, and a higher disease burden in Midland and the surrounding areas in close proximity to the dioxin contaminated areas.ConclusionThese findings suggest that increased breast cancer incidences are spatially associated with soil dioxin contamination. Aging is a substantial factor in the development of breast cancer. Findings can be used for heightened surveillance and education, as well as formulating new study hypotheses for further research.

Highlights

High levels of dioxins in soil and higher-than-average body burdens of dioxins in local residents have been found in the city of Midland and the Tittabawassee River floodplain in Michigan
Previous studies have reported higher than normal levels of dioxins in some locations in the city of Midland and Tittabawassee River floodplain in Michigan (Figure 1); while dioxin concentration in soils upstream of the river is similar to background levels across Michigan [1,2,3,4,5]
From 1985 to 2002, there was an increasing trend in the number of breast cancer cases in females between 45 and 64 years old in Midland, Saginaw, and Bay Counties (Figure 2) with an annual percent change (APC) of 0.43, which is slightly higher than the national trend (0.4) during the approximately same period [24]

Summary

Introduction

High levels of dioxins in soil and higher-than-average body burdens of dioxins in local residents have been found in the city of Midland and the Tittabawassee River floodplain in Michigan. The objective of this study is threefold: (1) to evaluate dioxin levels in soils; (2) to evaluate the spatial variations in breast cancer incidence in Midland, Saginaw, and Bay Counties in Michigan; (3) to evaluate whether breast cancer rates are spatially associated with the dioxin contamination areas. Previous studies have reported higher than normal levels of dioxins in some locations in the city of Midland and Tittabawassee River floodplain in Michigan (Figure 1); while dioxin concentration in soils upstream of the river is similar to background levels across Michigan [1,2,3,4,5]. Inspired by the increased concern regarding the possible health effects, this study aimed at evaluating the soil dioxin contamination and exploring the potential risks associated with breast cancer incidence in the region

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