Pendimethalin doesn’t harm established turfgrass.

How Long Does Pendimethalin Last?

by Amanda Flanigan

Before using any chemical in or around their home, mothers should research the product and learn the health and environmental effects associated with the chemical. Pendimethalin is one such gardening product that if not used properly can pose a risk to your children. By familiarizing yourself with the ins and outs of this product, you will help keep your family safe.

What is Pendimethalin?

Pendimethalin is the active ingredient in various pre-emergent and post-emergent herbicides used to control certain species of annual grasses and broadleaf weeds, including crabgrass. It is available in various forms including liquid and granular. Most brands of herbicide containing pedimethalin state that the chemical needs about 1/2 inch of rainfall to be activated. If the area isn’t covered isn't watered, the effectiveness of the herbicide will be inconsistent.

How Long Does it Persist?

The half-life of pendimethalin is the amount of time it takes for 50 percent of the product to degrade. The Extension Toxicology Network website states that the half-life of pendimethalin is about 40 days. This period varies depending on environmental factors such as temperature and moisture levels of the soil. Most soils adsorb pendimethalin, meaning it binds on the surface, and increasing the clay and organic matter in the soil improves the chemical's binding capacity; this means the herbicide has a low chance of leaching into ground water. Pendimethalin is absorbed through plant roots, and interferes with cell division. According to the Extension Toxicology Network website, this herbicide isn’t absorbed through the blades of grasses and plants only take up a small amount of the chemical from the soil.

Health Effects of Exposure

Pendimethalin exposure can occur through direct contact with the herbicide, inhalation of the dust or vapors, absorption through skin or ingestion from plants sprayed with the chemical. Pendimethalin has a low toxicity, according to the EPA. It can, however, pose a risk if it comes in contact with the eyes or is ingested. When ingested, most of the pendimethalin is excreted with a low amount being absorbed by the bloodstream. What is absorbed through the bloodstream becomes metabolized quickly in the liver and kidneys before being expelled from the body in the urine. Pendimethalin is typically not toxic if inhaled or absorbed through the skin. It is reported to be a mild skin irritant and "inhalation of dusts or fumes may be mildly to moderately irritating to the linings of the mouth, nose, throat and lungs," according to Extension Toxicology Network. The EPA lists pendimethalin as a possible cancer-causing substance and it has been shown to cause thyroid problems in lab rats.

Warnings, Precautions and Considerations

When using pendimethalin herbicides, keep children and pets out of the area while applying the chemical. Don’t allow them to enter the area until the dust has settled or -- if in liquid form -- the solution has dried. If the pendimethalin comes in contact with skin or eyes, flush the area with cool water for about 20 minutes. Contact poison control if the herbicide is ingested. Though animal studies recorded no birth defects as a result of ingestion of pendimethalin, pregnant and nursing women should err on the side of caution and avoid this herbicide.

About the Author

Amanda Flanigan began writing professionally in 2007. Flanigan has written for various publications, including WV Living and American Craft Council, and has published several eBooks on craft and garden-related subjects. Flanigan completed two writing courses at Pierpont Community and Technical College.

Photo Credits

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