Figure 1

Average levels of arsenic (A), cadmium (B), manganese (C), and lead (D) within census tracts across North Carolina. The color gradient represents the calculated exposure percentile categories (≤50^th; 50-75^th; 75-90^th; ≥90^th percentiles). The dark brown category represents exposed tracts and the light yellow category represents unexposed tracts that were used to assess the association with birth defects prevalence. Gray areas had fewer than 10 tested wells and were excluded from the analysis.