Overview

• Researchers analyzed 357,741 Iowa birth records from 1970 to 1988 and matched them to county-level nitrate measurements taken within 30 days of conception
• Exposure above 0.1 mg/L of nitrate was associated with a 0.66 percentage-point rise in preterm births and levels above 5 mg/L increased low birthweight risk by 0.33 percentage points
• Groundwater nitrate concentrations climbed by an average of 8% per year during the study period, yielding a mean exposure of 4.2 mg/L
• The EPA’s current 10 mg/L contaminant limit, set in 1992, does not account for prenatal impacts and may leave mothers and infants unprotected
• Authors stress that no prenatal nitrate exposure level is safe—equating its harm to about 15% of that from maternal smoking—and call for updated standards and more comprehensive water quality data