This is a fact sheet about a chemical that may be found in some public or
private drinking water supplies. It may cause health problems if found
in amounts greater than the health standard set by the United States
Environmental Protection Agency (EPA).
What is Diquat and how is it used?
Diquat is an organic solid of colorless or yellow crystals. A water
solution is dark red-brown. Diquat is a herbicide that has been used
extensively in the US since the late 1950s to control both crop and
aquatic weeds. It is used on potatoes; as an aid in harvesting cotton,
rapeseed and other oil seed crops; to wilt and dry out silage, standing
hay, etc. for storage; a plant growth regulator and sugar cane-flowering
The list of trade names given below may help you find out whether you
are using this chemical at home or work.
Trade Names and Synonyms:
Why is Diquat being regulated?
In 1974, Congress passed the Safe Drinking Water Act. This law requires
EPA to determine safe levels of chemicals in drinking water which do or
may cause health problems. These non-enforceable levels, based solely on
possible health risks and exposure, are called Maximum Contaminant Level
The MCLG for diquat has been set at 20 parts per billion (ppb)
because EPA believes this level of protection would not cause any of the
potential health problems described below.
Based on this MCLG, EPA has set an enforceable standard called a
Maximum Contaminant Level (MCL). MCLs are set as close to the MCLGs as
possible, considering the ability of public water systems to detect and
remove contaminants using suitable treatment technologies.
The MCL has been set at 20 ppb because EPA believes, given present
technology and resources, this is the lowest level to which water
systems can reasonably be required to remove this contaminant should it
occur in drinking water.
These drinking water standards and the regulations for ensuring
these standards are met, are called National Primary Drinking Water
Regulations. All public water supplies must abide by these regulations.
What are the health effects?
Short-term: EPA has found diquat to potentially cause the following health
effects when people are exposed to it at levels above the MCL for
relatively short periods of time: dehydration.
Long-term: Diquat has the potential to cause the following effects
from a lifetime exposure at levels above the MCL: cataracts.
How much Diquat is produced and released to the environment?
Diquat usage in 1980 was estimated to be 200,000 lbs. of active
ingredient. 1982 data indicates that diquat was not produced
domestically, but imports were nearly 835,000 lbs. Diquat is released
into the environment during its use as a contact herbicide, aquatic weed
control agent, harvesting aid, or plant growth regulator. It may also be
released into wastewater or in spills during its manufacture, transport
What happens to Diquat when it is released to the environment?
Diquat rapidly adheres to soil particles. Though it is resistant to
breakdown by microbes or other means, this binding to soil serves to
Diquat is removed rapidly from water, disappearing in 2-4 weeks. It has
little or no tendency to accumulate in fish.
How will Diquat be detected in and removed from my drinking
The regulation for diquat became effective in 1994. Between 1993 and 1995,
EPA required your water supplier to collect water samples every 3 months
for one year and analyze them to find out if diquat is present above 0.4
ppb. If it is present above this level, the system must continue to
monitor this contaminant.
If contaminant levels are found to be consistently above the MCL,
your water supplier must take steps to reduce the amount of diquat so
that it is consistently below that level. The following treatment
methods have been approved by EPA for removing diquat: Granular
How will I know if Diquat is in my drinking water?
If the levels of diquat exceed the MCL, 20 ppb, the system must notify the
public via newspapers, radio, TV and other means. Additional actions,
such as providing alternative drinking water supplies, may be required
to prevent serious risks to public health.
This is a factsheet about a chemical that may be found in some
public or private drinking water supplies. It may cause health problems
if found in amounts greater than the health standard set by the United
States Environmental Protection Agency (EPA).
Drinking Water Standards:
Note: This fact sheet is part of a larger publication
adapted from U.S. EPA publication: EPA National Primary Drinking Water
|Mclg: 20 ppb (parts per billion)
Mcl: 20 ppb