What is Metolachlor and Why Does It Matter?

Metolachlor is a weed killer (herbicide) used widely on corn, soybeans, and sorghum crops. Farmers apply it to soil before or just after planting to stop weeds from taking hold. Rain and irrigation water then carry it off fields and into streams, rivers, and groundwater. From there, it can work its way into municipal water supplies. The EPA classifies metolachlor as a possible human carcinogen based on animal studies.

The compound has been detected in 174 water systems across the United States, according to monitoring data. The average level found is 0.295 parts per billion (ppb), with the highest recorded sample reaching 4.6 ppb. While no systems in this dataset tested above the current regulatory limit, that doesn't mean exposure is risk-free. The EPA's legal limit and the health-protective guidelines set by the Environmental Working Group (EWG) are two very different numbers — and the gap between them matters.

At low, chronic exposure levels, metolachlor raises concern primarily because of its potential to disrupt hormones and its possible links to cancer. Animal studies have shown liver and kidney stress at higher doses (EPA). The EWG has flagged metolachlor as a contaminant of concern, particularly for children and pregnant women, whose developing systems are more sensitive to chemical exposure. It's worth noting that "legal" doesn't always mean "safe." The EPA sets enforceable limits based on a balance of health risk, treatment cost, and detection technology — not purely on what scientists consider the safest possible level.

Geographically, metolachlor detections follow a clear pattern: they cluster in America's agricultural heartland. Texas leads with 46 affected systems, followed by Wisconsin (38), Kansas (30), Missouri (13), and Nebraska (10). These states share something obvious — they're major corn and soybean producers. Metolachlor is one of the most heavily used herbicides in the U.S., with millions of pounds applied each year across Midwest and Southern farmland. Spring and early summer bring the highest runoff risk, right when fields are freshly treated and rain events are common. If you live in a rural or semi-rural community in any of these states, your water source may be more vulnerable than you realize.

The good news is that metolachlor is removable. Activated carbon filtration — the kind found in many under-sink and countertop filters — can reduce metolachlor levels significantly. For the most thorough protection, a reverse osmosis (RO) system is the gold standard. RO systems push water through a fine membrane that blocks pesticides, herbicides, and many other contaminants, removing up to 99% of what's in your water. Echo Water's reverse osmosis systems are designed specifically for home use, giving your family clean water straight from the tap without the hassle of bottled water. If you're in Texas, Wisconsin, Kansas, Missouri, or Nebraska — or anywhere with heavy agricultural activity nearby — an RO system is a smart investment.

You can also check your local water utility's annual Consumer Confidence Report (CCR), which is required by law to list detected contaminants and their levels. If metolachlor shows up in your report, even below the legal limit, it's a signal worth taking seriously. Pairing that information with a quality home filter puts you in control of what your family actually drinks.

Regulatory Standards for Metolachlor

Cities With the Highest Metolachlor Levels

States Most Affected by Metolachlor

Frequently Asked Questions

Related Contaminant Guides