Atrazine

Atrazine was developed by Syngenta (formerly Ciba-Geigy) in the late 1950s and registered in the US in 1959 [1]. It quickly became indispensable to corn farming because it effectively controls broadleaf and grass weeds and is cheap. Today, about 80 million pounds are applied annually in the US, primarily to corn in the Midwest. Atrazine is banned in the European Union due to its persistent groundwater contamination — it has appeared in European groundwater at levels exceeding EU standards — but remains legal in the US despite similar contamination patterns [2]. The research that most dramatically illustrated atrazine's endocrine effects came from UC Berkeley biologist Tyrone Hayes, who showed that male frogs exposed to concentrations as low as 0.1 ppb — well below the US drinking water standard of 3 ppb — were chemically feminized: they produced eggs in their testes and had suppressed testosterone. Syngenta's aggressive efforts to discredit Hayes' research were later documented in a Senate Environment Committee investigation [3].

Drinking water in the Midwest is the most significant exposure route: atrazine runs off cornfields into streams, rivers, and aquifers after spring planting rains [1]. USGS surveys show atrazine in more than 90% of corn-belt stream samples during spring planting season. Municipal water systems in the Midwest treat for atrazine, but rural residents on private wells may have unmonitored levels. Atrazine-contaminated groundwater affects an estimated 7.6 million Americans according to USDA estimates [2]. Food exposure occurs through residues on crops (corn, sorghum) and through meat and dairy from animals in atrazine-using regions, though food residues are generally lower than water residues. Occupational exposure for farmers and applicators occurs through inhalation and dermal contact during application [3].

Atrazine's primary mode of action relevant to human health is aromatase induction — it activates the enzyme that converts androgens (male hormones) into estrogens [1]. This hormonal interference is most damaging during fetal development and puberty, when hormone-directed tissue development is occurring. Animal studies show feminization of male offspring, reduced sperm quality, earlier puberty in females, and suppressed immune function [2]. Human epidemiological evidence links atrazine exposure (measured by urinary metabolites or proximity to high-use areas) to birth defects (particularly gastroschisis and choanal atresia), small-for-gestational-age births, early puberty in girls, and hormonal disruption. A 2011 EPA technical review noted the science on reproductive effects was concerning but stopped short of restricting use [3].

Pregnant women living in the rural Midwest and drinking private well water or unfiltered surface water during the April–July application season face the highest exposures [1]. Infants whose formula is prepared with atrazine-contaminated water receive the highest doses per body weight. Farm applicators and farmers who handle atrazine concentrate during mixing and loading operations have significant skin and inhalation exposure [2]. Communities downstream from major corn-growing areas on the Mississippi, Illinois, and Ohio rivers have elevated water exposures. People who garden or live adjacent to corn or sorghum fields in areas of regular atrazine application may have soil and air exposure during application.

Install a reverse-osmosis or activated-carbon block filter certified for atrazine on your kitchen tap if you live in the Midwest and use private well or surface water [1]. The EPA drinking water maximum contaminant level is 3 ppb, but the EWG recommends treating water at any detectable level for infants and pregnant women. Test your well water in spring (April–June) when atrazine runoff peaks — county extension offices often facilitate affordable testing [2]. Choose organic corn products (popcorn, corn tortillas, cornmeal) to avoid atrazine residues. During application season near agricultural areas, keep windows closed on windy days and avoid outdoor exercise downwind of fields. Support your local water utility's disclosure of atrazine levels — utilities that draw from the Mississippi River system should report seasonal peak concentrations [3].