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Atrazine and herbicides in drinking water

Atrazine is one of the most widely used herbicides in the United States, applied primarily to corn. It is a frequent contaminant of surface water in agricultural watersheds, with seasonal spikes in late spring and early summer that the annual-average MCL can mask. EPA's MCL is 0.003 mg/L (3 ppb). Atrazine has been banned in the European Union since 2004.

Where atrazine in drinking water comes from

Atrazine is a triazine herbicide used to control broadleaf and grassy weeds, primarily on corn, sorghum, and sugarcane. Roughly 70 million pounds are applied per year in the U.S., almost all of it in the corn belt: Iowa, Illinois, Indiana, Nebraska, Minnesota, and parts of Ohio and Missouri. The Mississippi River basin and tributaries (Missouri, Ohio, Illinois rivers) carry detectable atrazine through most of the growing season.

Surface-water systems that draw from rivers and reservoirs in agricultural watersheds are the most affected. Groundwater systems in those regions also see atrazine but at lower levels.

The seasonal-peak problem

Atrazine concentrations in drinking water are not flat through the year. They follow a sharp peak in May and June, when post-emergence applications run off into rivers after spring rainstorms. Peak weekly concentrations in some Midwestern utilities reach 10-30 ppb (above the MCL) for a few weeks each year, with low values the rest of the year.

The MCL of 3 ppb is enforced as an annual running average. A utility can be in compliance with the annual rule while serving water at several times the MCL for several weeks every spring. This is the central public-health critique of the standard, especially for pregnant people whose first-trimester exposure may align with the spring peak.

Why it matters for health

Atrazine is an endocrine disruptor. Animal studies show effects on reproductive hormones at sub-MCL exposures. Specific concerns from human epidemiology and animal research:

  • Pregnancy outcomes: lower birth weight and slight increases in several birth defects in studies of agricultural communities.
  • Hormonal effects: documented disruption of estrogen synthesis in laboratory models.
  • Possible carcinogen: classified by IARC as Group 3 (not classifiable as to carcinogenicity to humans) but under continuing review.

The European Union banned atrazine in 2004, specifically because regulators determined that safe drinking-water levels could not be reliably achieved given application patterns. The U.S. EPA has reauthorized atrazine multiple times, most recently in 2020, with revised aquatic-life protections but unchanged drinking-water rules.

What to do

  1. If your utility serves a Midwestern agricultural watershed, ask for monthly atrazine data during May to July. Annual averages can hide the spring spike.
  2. Granular activated carbon (GAC) filtration is effective. Many large utilities in atrazine country already run GAC at the treatment plant.
  3. For point-of-use, choose an NSF/ANSI 53 filter with a VOC reduction claim. Reverse osmosis also works.

This page is general information, not medical advice.

Sources

Editorial review: reviewed 2026-05-11 by RK 2026-05-11. Editorial standards.