NIOSH logo and tagline

New Study First to Describe Scope of Illness Associated with the Use of Two Common Herbicides

February 3, 2016
NIOSH Update:

Contact: Stephanie Stevens (202) 245-0641

A majority of herbicide-related deaths are caused by just two of the more commonly used weed killers—paraquat and diquat—and despite its toxicity, most cases of illness related to paraquat poisoning were low to moderately severe according to new research published in the journal, Environmental Research by the National Institute for Occupational Safety and Health (NIOSH).

To identify the magnitude of illness attributed to the use of paraquat and diquat in the U.S., as well as the causes of illness, researchers examined combined data from three sources from 1998 to 2011: the NIOSH Sentinel Event Notification System for Occupational Risks (SENSOR)-Pesticides Program; the California Department of Pesticide Regulation Pesticide Illness Surveillance Program; and the U.S. Environmental Protection Agency, Office of Pesticide Programs’ Incident Data System. Additionally, researchers assessed data from a national database, the National Poison Data System, for national trends of paraquat- and diquat-related illnesses.

“This is really the first time we’ve looked at the extent of illness caused by these herbicides,” said NIOSH Director John Howard, MD. “We now know that all of the cases of illness and death related to these products are preventable, which will help us identify ways to better protect both the workers who need to use these products as part of their job and others exposed to these potentially harmful chemicals.”

The study found 300 paraquat- and 144 diquat-related acute illnesses were reported in 35 states and 1 U.S. territory; 76 percent of paraquat-related cases were work-related. While the majority of cases of paraquat-related illness were low to moderately severe—health effects commonly included skin, eye, or neurological symptoms—researchers identified several deaths. Compared to other pesticides, paraquat or diquat was responsible for the majority, 85 percent, of herbicide-related deaths in the U.S.

Of the cases reported, 43 individuals ingested paraquat and 25 ingested diquat. The majority of ingestion cases were unintentional and frequently occurred because the pesticides were improperly stored (e.g. in beverage bottles).

Failure to wear Personal Protective Equipment (PPE), especially eye protection, was the most common reason people were sickened by paraquat; other causes included drift from the pesticide application site and accidental spills or splashes. For diquat, the most common cause of illness stemmed from application equipment failure followed by accidental spills or splashes.

“When less harmful weed control options aren’t an option, these findings suggest that additional training and stricter compliance with label instructions to ensure proper herbicide storage and PPE use are important measures to help prevent illness or even death,” said NIOSH Medical Officer and senior study author Geoff Calvert, MD, MPH.

For access to a copy of the study please visit: For more information about the Sentinel Event Notification System for Occupational Risk (SENSOR) visit

NIOSH is the federal agency that conducts research and makes recommendations for preventing work-related injuries, illnesses, and deaths. For more information about NIOSH visit