A new study published in Environmental Science: Advances offers the most comprehensive analysis to date of fluoride concentrations in Iowa’s groundwater and treated drinking water. The research, led by scientists from the University of Iowa, reveals significant regional variability in fluoride levels and underscores the need for tailored water management strategies to balance dental health benefits with potential risks of overexposure.

Key findings include:

• Fluoride concentrations in untreated groundwater ranged from <0.1 to 11.2 mg/L, with a median of 0.35 mg/L—below the U.S. Public Health Service’s recommended level of 0.7 mg/L for dental health.
• Approximately 7% of groundwater samples exceeded the EPA’s secondary maximum contaminant level (SMCL) of 2 mg/L, and 0.4% exceeded the maximum contaminant level (MCL) of 4 mg/L.
• Treated drinking water had a higher average fluoride concentration of 0.87 mg/L, reflecting fluoridation practices. However, 285 samples from 56 systems exceeded the SMCL since 2000, with one sample surpassing the MCL.
• Elevated fluoride levels were most common in deeper wells and aquifers such as the Cambrian-Ordovician and Mississippian, which contain fluoride-bearing minerals and have longer groundwater residence times.
• Proximity to the Manson Impact Structure—a crater in north-central Iowa—was associated with significantly higher fluoride concentrations in groundwater.

The study analyzed nearly 9,000 groundwater samples and over 26,000 treated water samples collected between 1931 and 2021. Researchers used geospatial mapping and statistical modeling to identify trends by aquifer type, landform region, and water source.

While community water systems (CWSs) have largely succeeded in maintaining fluoride levels within recommended ranges, the study highlights concerns for the estimated 230,000 Iowans who rely on private wells. These wells are not regulated and may draw from aquifers with naturally higher fluoride concentrations.

The authors call for increased monitoring and public awareness, especially in regions with geologic vulnerabilities. They also emphasize the importance of balancing fluoridation’s dental health benefits with the risks of excessive exposure, such as dental fluorosis and other potential health effects.

The full article is available online at Environmental Science: Advances.