Atrazine in Drinking Water: Risks from America's Most Common Herbicide

Atrazine is one of the most heavily applied pesticides in the United States, and it shows up in drinking water across the Corn Belt every spring. It is regulated, it is mobile, and it spikes on a predictable seasonal cycle tied to corn planting. This profile explains where atrazine comes from, what it does to the body, how it is regulated, and how households on affected systems can remove it.

What Is Atrazine?

Atrazine is a synthetic triazine herbicide used to control broadleaf and grassy weeds, primarily in corn, sorghum, and sugarcane. It is the second most widely used herbicide in the United States, behind only glyphosate, with roughly 70 to 80 million pounds applied annually across US agriculture. Its chemical name is 6-chloro-N-ethyl-N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine, and its chemical formula is C8H14ClN5.

Atrazine works by blocking photosynthesis in susceptible plants. Farmers apply it pre-emergence and early post-emergence, typically between late April and early June across the Midwest. Because a single application covers a long stretch of the growing season, it remains one of the cheapest and most effective weed controls available for row crops.

The properties that make atrazine useful in agriculture also make it a problem for drinking water. It is moderately water-soluble and only weakly bound by soil, which means rainfall and irrigation carry it off treated fields into surface water. Once in groundwater, it degrades slowly, persisting for months to years depending on conditions. Its half-life in soil ranges from roughly 60 to more than 100 days; in cold, anaerobic groundwater, that can stretch significantly longer.

Pure atrazine is a colorless crystalline solid with only a faint chemical odor at high concentrations. At the levels found in finished drinking water, it is undetectable by taste or smell, which is why monitoring rather than sensory judgment is the only reliable way to know if it is present.

The European Union banned atrazine use in 2004 after repeated detections above its 0.1 ppb drinking water limit. It remains registered for use in the United States, with EPA having reapproved it through a series of contested re-registration decisions. Canada, Australia, and most of South America still permit it as well, though typically with tighter application restrictions than in the US.

How Atrazine Gets Into Drinking Water

Atrazine enters public water systems and private wells almost entirely through agricultural use. The pathway varies by geography and season, but four mechanisms dominate.

Agricultural Runoff

Runoff from corn fields is the primary pathway. Atrazine is sprayed pre-emergence in spring; the first heavy rain after application washes a fraction of the dose into ditches, streams, and reservoirs. Surface water systems that draw from rivers and impoundments in corn-heavy watersheds see their sharpest atrazine peaks within days of these storm events. Co-occurring contaminants from the same runoff include nitrate and other pesticides.

Groundwater Infiltration

Where soils are sandy or fractured, atrazine leaches downward into shallow aquifers. Once in groundwater, it degrades slowly because subsurface environments have little sunlight and fewer microbes capable of breaking the triazine ring. Wells in corn-growing regions with permeable soils are the most commonly affected; atrazine has been detected in shallow wells for years after the nearest application.

Seasonal Spikes

Atrazine concentrations in Corn Belt surface water typically peak from late May through July, often running 5 to 20 times the annual average during post-application storm events. A reservoir that reads 1 ppb in February can climb above 10 ppb in June, then decline through the fall. This seasonality is the defining feature of atrazine exposure and the reason EPA chose an annual-average regulatory structure rather than a single-sample limit.

Degradates in Water

Atrazine breaks down into several related compounds: deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DACT). These degradates share the triazine core and have similar, though generally weaker, biological activity. EPA regulates atrazine plus three chlorotriazine metabolites as a total residue under the drinking water rule, meaning the MCL applies to their combined concentration rather than to atrazine alone.

Geographic Hotspots

Region	Context
Central Corn Belt (IL, IA, IN, OH, MO)	Peak seasonal detections; multiple municipal systems have exceeded the MCL briefly in spring
Missouri River basin	Nebraska, Kansas, and Iowa show watershed-wide elevations during application season
Ohio River basin	Indiana, Ohio, and Kentucky surface water systems see seasonal spikes
Chesapeake Bay watershed	Maryland and Pennsylvania report limited but repeated detections
Louisiana sugarcane country	Less studied than the Corn Belt but documented in regional surveys

Atrazine commonly co-occurs with nitrate, arsenic in some geologies, and emerging contaminants like 1,4-dioxane and PFAS in watersheds with mixed industrial and agricultural inputs.

Health Effects

Atrazine’s central health concern is not acute toxicity; it is endocrine disruption. EPA classifies atrazine as “not likely” to be a human carcinogen at the doses relevant to drinking water exposure, but it is widely recognized as an endocrine disruptor that alters hormone signaling in animals and in laboratory studies. That distinction — low cancer risk at regulated doses, meaningful hormonal activity — shapes both the science and the regulatory debate.

Endocrine Disruption (Primary Concern)

Atrazine interferes with estrogen, androgen, and thyroid hormone pathways. The most widely cited mechanistic work comes from biologist Tyrone Hayes, whose studies documented demasculinization and feminization in male frogs exposed to environmentally relevant concentrations, including reduced testosterone, abnormal gonadal development, and in some cases functional sex reversal. Hayes’s findings have been contested by the manufacturer but replicated in parts by independent laboratories, and EPA’s scientific advisory panels have acknowledged the endocrine signal while debating how to translate it into a human drinking water standard.

Reproductive and Developmental Effects

Rodent studies show delayed puberty, altered luteinizing hormone patterns, and disrupted prenatal development after atrazine exposure. Human epidemiology is more limited but suggests associations between atrazine exposure and menstrual cycle irregularities, changes in hormone levels, and small increases in preterm birth rates in high-exposure agricultural communities. The epidemiological signal is not uniform across studies, and confounding from co-exposure to other pesticides is difficult to rule out.

Cancer (Mixed Evidence)

The International Agency for Research on Cancer (IARC) classifies atrazine as Group 3, not classifiable as to its carcinogenicity to humans, based on inadequate evidence in humans and limited evidence in animals. EPA’s own cancer classification concludes that atrazine is “not likely” carcinogenic at the doses used to set the drinking water standard. Individual studies have suggested associations with ovarian, breast, and prostate cancers, but the evidence has not been consistent enough for regulators to use it as the primary endpoint.

Children and Pregnant Women

Developing endocrine systems are the most sensitive target. Placental transfer of atrazine has been documented in animal models, and breast milk can carry small amounts in exposed mothers. Public health guidance in affected regions typically emphasizes that pregnant women, infants, and young children should avoid drinking water known to exceed the MCL even briefly.

Controversy

Atrazine’s 2003 EPA re-registration and subsequent reviews have been repeatedly contested. Environmental groups and several states have petitioned for a lower MCL, pointing to the endocrine data and to California’s much stricter Public Health Goal. The manufacturer and industry groups argue that the current 3 ppb annual-average standard is protective and that short seasonal exceedances do not produce harmful long-term exposure. The debate remains unresolved, and atrazine continues to be one of the more politically charged pesticide decisions at EPA.

EPA Regulation and Limits

EPA set the Maximum Contaminant Level (MCL) for atrazine at 3 ppb (3 ug/L) under the 1991 Phase II Rule, and it has remained there since. The MCL applies as a running annual average rather than as a single-sample ceiling. EPA also set the Maximum Contaminant Level Goal (MCLG) at 3 ppb, matching the MCL, based on a non-cancer endpoint tied to the hormonal and reproductive effects observed in animal studies.

The running-average structure is unusual among drinking water standards and was designed specifically to accommodate atrazine’s sharp seasonal behavior. A system can read above 3 ppb during a May storm event without triggering an immediate violation, as long as the four-quarter running average stays below 3 ppb. Environmental groups have long argued that this structure masks real short-term exposure; EPA has defended it on the grounds that health effects are driven by chronic rather than acute dose.

Standard	Value	Notes
EPA MCL	3 ppb (annual average)	Set 1991; atrazine plus three chlorotriazine metabolites
EPA MCLG	3 ppb	Matches MCL; based on non-cancer endpoint
EU Drinking Water Directive	0.1 ppb (per individual pesticide)	EU banned atrazine use in 2004
California Public Health Goal	0.15 ppb	Non-enforceable health target, much stricter than federal
Minnesota Drinking Water Advisory	3 ppb	Matches federal
EPA Aquatic Life Benchmark	Chronic 1 ppb	Ecological threshold below the human MCL

Community water systems in affected regions are required to monitor atrazine quarterly during the growing season; systems with historically low detections may be placed on reduced schedules. Violations are reported through EPA’s Safe Drinking Water Information System (SDWIS).

How Widespread Is Atrazine?

USGS has documented atrazine detection in the majority of Midwestern surface water samples collected during the growing season. Broad syntheses of USGS and USDA monitoring have found atrazine exceeding 3 ppb in roughly 1 in 4 sampled Corn Belt streams during peak application months, though the exact share varies by year and by watershed.

On the finished-water side, a smaller but persistent group of community water systems have recorded running-annual-average exceedances of the MCL at some point in their history; published reviews have identified on the order of several dozen such systems, concentrated in Illinois, Indiana, Iowa, and Ohio. Many more systems see short-term spikes above 3 ppb in raw or finished water without exceeding the annual average.

Private wells in corn-growing regions commonly show low-level atrazine detections, especially where shallow aquifers underlie sandy or tile-drained fields. Short-term post-storm concentrations above 30 to 40 ppb have been documented in some small-system raw water, though utilities typically blend across multiple intakes, adjust treatment, or use activated carbon to bring tap-water concentrations well below the MCL.

Outside the Corn Belt, atrazine detections are generally low or absent. Urban systems drawing from non-agricultural watersheds and well-protected groundwater sources in the Northeast, Mountain West, and Pacific Northwest rarely show measurable atrazine. Detection trends have been relatively stable over the past two decades; total US atrazine use has declined modestly as some acres have shifted to glyphosate-tolerant corn, but the underlying seasonal pulse in Corn Belt surface water remains the dominant signal. Climate-driven changes in rainfall timing and intensity appear to be shifting peak concentrations later into summer in some watersheds, which has implications for utilities that plan their carbon regeneration schedules around historical application windows.

How WaterVerge Tracks Atrazine

WaterVerge pulls atrazine monitoring data from EPA SDWIS. Atrazine is a regulated organic contaminant, and community water systems in affected regions test quarterly during peak application season, with additional sampling triggered by prior detections or known vulnerability.

City pages on WaterVerge display the most recent atrazine result for the serving utility, flag any historical exceedances of the 3 ppb running annual average, and show the date of the last sample. Violations appear on the utility’s compliance record alongside other regulated contaminants.

Private wells are not covered by SDWIS or by any federal monitoring program. If you draw from a private well in the Corn Belt or in a sugarcane-growing region, home testing through a certified laboratory is the only way to know your atrazine exposure. A lab-analyzed pesticide panel typically runs $100 to $200 and covers atrazine along with common co-occurring herbicides and insecticides. See our guides on well water testing and how to test your tap water.

How to Remove Atrazine

Start with what does not work. Standard ion-exchange water softeners do not remove atrazine; they target calcium and magnesium, not neutral organic molecules. Boiling does not remove atrazine either. Atrazine is thermally stable at boiling temperatures, and evaporation can actually concentrate it in the remaining water.

Method	Removal Rate	Certification	Best For
Activated carbon block	85-99%	NSF/ANSI 53 pesticide reduction	Under-sink, pitcher
Reverse osmosis	85-95%	NSF/ANSI 58	Under-sink, comprehensive
Granular activated carbon (GAC) whole-house	80-95%	NSF/ANSI 42/53	POE for well water
Ozone + UV advanced oxidation	90-99%	Municipal scale	Utility-scale treatment
Standard sediment filter	Negligible	N/A	Not effective for atrazine

A high-quality activated carbon block filter certified to NSF/ANSI 53 for pesticide reduction is the most accessible household solution. Carbon binds the triazine ring through hydrophobic and pi-pi interactions, and a well-designed block can pull finished water from a few ppb down to below detection. Look for products that specifically list atrazine on their NSF/ANSI 53 certification; generic “carbon filter” claims are not sufficient.

Reverse osmosis is effective but slightly less so than carbon for atrazine specifically. Atrazine is a relatively small polar molecule, and while RO membranes reject most of it, a well-maintained carbon block often outperforms RO head-to-head on this single contaminant. Most under-sink RO units include a carbon post-filter, which is part of why they achieve their published removal rates. See best reverse osmosis systems and best under-sink water filters for specific product recommendations.

For private wells in corn-growing regions, whole-house GAC is the standard recommendation. A point-of-entry GAC unit sized appropriately for household flow will knock atrazine down across every tap, including the shower and laundry. Carbon beds need replacement on a schedule that depends on water volume and contaminant load; for seasonal atrazine exposure, replacing ahead of the spring runoff season is prudent. See best whole-house water filters.

At the municipal scale, utilities in heavily affected watersheds use powdered activated carbon (PAC) dosed seasonally ahead of peak runoff, permanent GAC contactor beds, or ozone paired with biologically active filtration. Advanced oxidation using ozone and UV, or ozone and hydrogen peroxide, can break the triazine ring itself rather than simply adsorbing the molecule, and it is increasingly used at larger Midwestern utilities. Some utilities have also built source-water protection programs with local farmers, paying for reduced atrazine application or conservation tillage on fields that drain to drinking water intakes. These programs are the only long-term solution that addresses the problem at the source rather than filtering around it downstream.

Pitcher and faucet filters are a reasonable interim choice if your utility has shown any atrazine detections in recent monitoring reports. Look specifically for the NSF/ANSI 53 pesticide reduction claim on the packaging — not all pitcher filters carry it, and the ones that do are usually carbon-block-based rather than loose-granular designs.

Check Your City

Atrazine exposure is concentrated in the Corn Belt and in sugarcane-growing regions. If you live in Illinois, Iowa, Indiana, Ohio, Missouri, Nebraska, Kansas, or Louisiana, it is worth checking whether your utility has recorded atrazine detections and when its last seasonal sample was taken. If you draw from a private well in any of these regions, a lab-analyzed pesticide panel is the only way to know. Search your city to see atrazine monitoring data, historical exceedances, and current violations for your water system.