Ecological Study Exploring Relationships between County Level Birth Defect Rates and Nitrate, Atrazine, and Other Nitrosatable Agrichemicals in Nebraska Groundwater

This ecological study evaluated relationships between birth defect rates and the presence of nitrate-N (NO3–N) and nitrosatable agrichemicals (e.g., atrazine) in Nebraska groundwater wells. County-level birth defect rates were positively correlated with county-specific percentages of wells containing both atrazine and NO3–N (p < 0.05); these percentages were also higher in counties with high (>303 affected births/10,000 births) compared to low rates (20.6% vs 5.5%; p < 0.05). In contrast, birth defect rates were negatively correlated with the percentages of wells positive for NO3–N only (p < 0.05), and these percentages were not significantly different between counties with high and low rates (91.3% vs 90.8%, respectively; p = 0.94). Counties with high birth defect rates also had significantly higher percentages of wells positive for atrazine only, and for NO3–N with any co-occurring nitrosatable agrichemical. Weighted Quantile Sum regression identified atrazine, metolachlor and transformation products of alachlor and acetochlor as major contributors to the positive association of the agrichemical mixture and birth defect rates. Results suggest that maternal exposure to co-occurring NO3–N and nitrosatable agrichemicals from drinking water is more detrimental to fetal development than exposure to the single compounds. Additional studies are needed to confirm and update our results at both aggregate and individual levels.