Picloram: The Contaminant in Tap Water You Didn't Know Was Harming Your Health

Written by Craig "The Water Guy" Phillips

Picloram is a long-lasting herbicide used to kill broadleaf weeds, brush and woody plants on rangeland, pastures, forests and rights-of-way such as roadsides, rail lines and power-line corridors. Because it dissolves easily in water and does not bind tightly to soil, it can wash into streams or leach into groundwater. The EPA limits picloram in public drinking water to 0.5 mg/L (500 ppb), mainly because long-term exposure above that level is linked to liver damage, and activated carbon is the EPA's recommended treatment.

What Picloram Is Used For

Picloram (4-amino-3,5,6-trichloropicolinic acid) is a systemic herbicide in the pyridine carboxylic acid family. It mimics a plant growth hormone, so treated broadleaf plants grow uncontrollably and die, while most grasses are left alone. It was introduced in the 1960s and is best known under the Tordon brand name; mixed with 2,4-D it was also the defoliant "Agent White."

Where it is used in the U.S. today:

• Rangeland and pasture , especially in the West, against invasive weeds such as knapweed, leafy spurge, mesquite and prickly pear.
• Forestry , for brush and woody-plant control and site preparation.
• Rights-of-way : roadsides, railways, pipelines and utility corridors, where crews need long-lasting vegetation control.
• Non-crop land such as industrial sites, often in mixes with 2,4-D or other herbicides.

It is not a typical lawn product. Many picloram products are restricted-use pesticides that only certified applicators can buy and apply.

How Picloram Gets Into Drinking Water

Picloram is one of the more persistent herbicides. The EPA's technical fact sheet gives a soil half-life of roughly 55 to more than 100 days, and it calls picloram the most persistent herbicide in its chemical group. Two properties make it a water concern:

• Runoff. Rain falling soon after application carries dissolved picloram from treated land into ditches, streams and reservoirs that may supply a treatment plant.
• Leaching. Because it binds weakly to soil, picloram can move down with rainwater into shallow aquifers, especially in sandy or gravelly soils with a high water table. That is the main risk for private wells near treated rangeland, forests or rights-of-way.

Spills, careless mixing near a wellhead and improper container disposal can create small but concentrated sources. In surface water, sunlight breaks picloram down faster (days to weeks), so groundwater is where it tends to linger.

Health Effects and the EPA Limit

Picloram is regulated under the Safe Drinking Water Act. The EPA has set both the health goal (MCLG) and the enforceable limit (MCL) at 0.5 mg/L, or 500 parts per billion . California's public health goal is the same 500 ppb.

• Long-term exposure above the MCL: liver damage. California's assessment is based on increased liver weight in animal feeding studies.
• Short-term exposure well above the MCL: the EPA lists effects on the central nervous system, weakness, diarrhea and weight loss. These are associated with concentrations far higher than are normally found in tap water.
• Cancer: the EPA has said there is inadequate evidence to determine whether picloram causes cancer from lifetime drinking water exposure.

Detections in public water supplies are uncommon and are usually far below the limit. The bigger unknown is private wells, which nobody is required to test.

Testing Your Water for Picloram

You can't taste, smell or see picloram, so a lab test is the only way to know.

• City water: public systems must monitor for picloram (initially four quarterly samples every three years, less often if nothing is detected). Check your utility's annual Consumer Confidence Report or ask the utility for its results.
• Private well: ask a state-certified lab for a chlorinated (acid) herbicide panel that includes picloram. EPA methods 515.1, 515.2 and 555 cover it. Home test strips for picloram aren't available.
• When to test: if your well is near rangeland, pasture, forestry operations, a rail line, a highway or a utility corridor that's sprayed, if you know of a spill, or if garden plants watered from the well show twisted, cupped leaves.

Treatment and Removal Options

Standard municipal treatment and chlorination don't reliably remove picloram, and boiling won't either. Options that do work:

• Granular activated carbon (GAC). This is the EPA's listed best available technology for picloram. Performance depends on contact time, the carbon used and how often you replace it. A whole-house carbon system treats every tap; a point-of-use carbon filter covers drinking water only. If you are pairing carbon with a softener, see how to combine a softener and a carbon filter .
• Reverse osmosis (RO). An under-sink reverse osmosis system with carbon pre- and post-filters reduces a wide range of organic chemicals in drinking and cooking water. Read about reverse osmosis drawbacks before you buy, and how to combine RO with a softener or UV .
• Water softeners do not remove picloram. A softener exchanges calcium and magnesium for sodium or potassium. It doesn't target herbicides. If you have both hard water and a herbicide concern, you need a softener and carbon or RO. See whether well water needs a filter and a softener .

For whole-house filtration, our Fluoride & Chlorine+ SUPER Filter combines catalytic carbon and bone char. Send us your lab results before choosing a system, so we can confirm it fits what's actually in your water. Whatever you install, replace the carbon or RO filters on schedule, because spent carbon stops adsorbing.

Picloram is one of many contaminants that can turn up in tap water; our guide to nickel in tap water covers another one that standard treatment can miss.

Reducing Your Risk if You Live Near Treated Land

• Know what's sprayed nearby. County weed-control offices, utilities and railroads can usually tell you which herbicides they use and when. Ask landowners leasing pasture or forest ground the same question.
• Protect the wellhead. Keep the well cap sealed and the ground around the casing sloped away so surface runoff can't pool there. Never mix or rinse herbicide sprayers near a well.
• Test after a change. Retest when a nearby property starts a spraying program, after a known spill, or if water from the well starts damaging garden plants.
• Use and dispose of products properly. If you apply herbicides yourself, follow the label exactly, avoid spraying before heavy rain, and take leftover product to a hazardous-waste collection site.
• Treat the water you drink first. If a test shows picloram, an under-sink carbon or RO system is the fastest, lowest-cost way to protect drinking and cooking water while you plan any whole-house treatment.

Frequently Asked Questions