Technical Factsheet on: DIQUAT
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
Drinking Water Standards
MCLG: 0.02 mg/L
MCL: 0.02 mg/L
HAL(child): none
Health Effects Summary
Acute: EPA has found diquat to potentially cause the following
health effects from acute exposures at levels above the MCL:
dehydration.
Drinking water levels which are considered "safe" for short-term
exposures have not been established.
Chronic: Diquat has the potential to cause the following health
effects from long-term exposures at levels above the MCL:
cataracts.
Cancer: There is inadequate evidence to state whether or not
diquat has the potential to cause cancer from a lifetime exposure
in drinking water.
Usage Patterns
Diquat is a herbicide that has been used extensively in the US
since the late 1950s to control both crop and aquatic weeds. Its
uses include potato haulm destruction; as a desiccant and
defoliant to aid harvesting cotton, rapeseed and other oil seed
crops; to pre-wilt silage, standing hay, etc. for storage; a
plant growth regulator and sugar cane-flowering suppressant.
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. In 1982 it was
estimated that diquat usage patterns were as follows:
Industrial/commercial uses, 67%; aquatic uses, 33%.
Release Patterns
Diquat is released into the environment during its use as a
contact herbicide, aquatic weed control agent, seed desiccant and
sugarcane flowering suppressant agent. It may also be released
into wastewater or in spills during its manufacture, transport
and storage.
Since diquat is not a listed chemical in the Toxics Release
Inventory, data on releases during its manufacture and handling
are not available.
Environmental Fate
Diquat is rapidly adsorbed by clay constituents of soil and in
the sorbed state is resistant to biodegradation and
photodegradation. The duration of residual activity in soil is a
few days; the deactivation resulting from its binding to the
soil. In some soils such as montorillonite clay, adsorption is
considered irreversible. There is some evidence of a more loosely
bound component, the fraction of which depends on the type of
soil.
Diquat is removed rapidly from aquatic systems, principally by
adsorption. If adsorption is initially to weeds, biodegradation
to soluble or volatile products occurs in several weeks. When
sorbed to sediment, little or no degradation probably occurs. In
any case, the diquat disappears from the water in 2-4 weeks.
Diquat will photodegrade in surface layers of water in 1-3 or
more weeks when not adsorbed to particulate matter.
Should diquat be released to the atmosphere during spraying
operations, it would be associated with aerosols. It will be
subject to photolysis (half-life approx 48 hrs) and gravitational
settling.
Little or no bioconcentration in fish will occur, as is expected
for a chemical whose log octanol/water partition coefficient is
-3.05. No residues were detected in organs or tissues of channel
catfish collected from pools 5 months after a single application
or 2 months after a second treatment of 1 ppm diquat.
Human exposure will principally be by agriculture workers or
others who use the chemical or are in the vicinity of fields or
bodies of water where diquat is used.
Chemical/ Physical Properties
CAS Number: 85-00-7
Color/ Form/Odor: Colorless to yellow crystals; water solution is
dark reddish brown
M.P.: 335-340 C B.P.: N/A
Vapor Pressure: 1.3x10-5 mm Hg at 20 C
Octanol/Water Partition (Kow): Log Kow = -3.05
Density/Spec. Grav.: 1.22 - 1.27 at 20 C
Solubility: 700 g/L of water at 20 C; Very soluble in water
Soil sorption coefficient: Koc N/A; very low mobility in soil
Odor/Taste Thresholds: N/A
Bioconcentration Factor: Not expected to bioconcentrate in
aquatic organisms.
Henry's Law Coefficient: N/A; no evaporation from water/soil
Trade Names/Synonyms: 1,1-Ethylene 2,2-dipyridylium dibromide;
Reglone
Other Regulatory Information
Monitoring For Ground/Surface Water Sources:
- Initial Frequency- 4 quarterly samples every 3 years
- Repeat Frequency- If no detections during initial round:
- 2 quarterly per year if serving >3300 persons;
- 1 sample per 3 years for smaller systems
- Triggers - Return to Initial Freq. if detect at > 0.0004 mg/L
Analysis:
| Reference Source |
Method Numbers |
| EPA 600/4-88-039 |
549.1 |
Treatment- Best Available Technologies:
Granular Activated Charcoal
For Additional Information:
EPA can provide further regulatory and other general information:
EPA Safe Drinking Water Hotline - 800/426-4791
Other sources of toxicological and environmental fate data include:
Toxic Substance Control Act Information Line - 202/554-1404
Toxics Release Inventory, National Library of Medicine - 301/496-6531
Agency for Toxic Substances and Disease Registry - 404/639-6000
National Pesticide Hotline - 800/858-7378
List of Contaminants
|
