| Chemical Abstract Number (CAS #) |
85007
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| Synonyms | Diquat dibromide |
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Dipyrido[1,2-a:2',1'-c]pyrazinediium, 6,7-dihydro-, dibromide | Aquacide | Dextrone | Reglone |
| Analytical Method |
EPA Method 549.1 |
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| Molecular Formula | C12H12N22Br |
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| Use | CONTACT HERBICIDE USED ALSO TO PRODUCE DESICCATION &
DEFOLIATION.
ITS USES INCL POTATO HAULM DESTRUCTION (420-840 G DIQUAT/HA)
USED AS DESICCANTS TO AID HARVESTING (ON COTTON, RAPE, & OTHER
OIL SEED CROPS, CEREALS, LUCERNE, ETC) & TO ASSIST IN THE CONSERVATION
OF FORAGE (PREWILTING FOR SILAGE, PREPN OF STANDING HAY, ETC).
HERBICIDE FOR INDUSTRIAL, COMMERCIAL, & AQUATIC USES.
SUGARCANE-FLOWERING SUPPRESSANT
Plant growth regulator
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| Consumption Patterns | HERBICIDE FOR INDUSTRIAL/COMMERCIAL USES, 67%; AQUATIC USES,
33% (1982)
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| Apparent Color | Colorless to yellow crystals
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| Melting Point | 335-340 DEG C
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| Molecular Weight | 344.07
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| Density | 1.22 TO 1.27 @ 20 DEG C/20 DEG
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| Sensitivity Data | Diquat concentrate may cause severe skin irritation and burning on contact. Contact with
dilute liquid or dust formulations of diquat may result in reversible skin irritation. Systemic
toxicity may occur from skin absorption, especially with repeated contact.
Contact with dilute liquid or dust (Diquat dibromide) formulations may cause reversible eye
irritation.
Some respiratory distress may be present in acute poisoning, but it is nonspecific.
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| Environmental Impact | Diquat is released to the environment during its use as a herbicide, seed dessicant, and
aquatic weed control agent. In the atmosphere, it will exist mainly as an aerosol and be subject to
photolysis (half-life approx. 2 days) and gravitational settling. It will tightly bind to the upper
layers of soil where it may remain for long periods of time. The binding to some soils is
considered to be irreversible and makes it unavailable for biodegradation and photodegradation.
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. Little or no bioconcentration in fish will occur. 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.
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| Environmental Fate | TERRESTRIAL 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 may be subject
to slow biodegradation.
AQUATIC FATE: Diquat is intentionally applied to water to control aquatic weeds. Diquat
disappeared from two experimental ponds within 14 and 30 days and was more persistent in the
pond that had a lower average temperature of 18 deg C . The most reasonable explanation for
the difference in persistence in the two ponds was a higher turbidity level and hence more
adsorption in the pond from which the diquat disappeared the fastest . When added to a
weed-infested simulated lake impoundment, it was initially adsorbed by the weeds. After complete
weedkill (4 days after treatment), biodegradation proceeded rapidly. After 22 days, only 1% of
the diquat remained in the water and 19% was adsorbed to sediment. The organically-bound
diquat was available for microbial degradation and formed water soluble and volatile products .
In other studies, diquat concentrations in a reservoir declined from 1000 to 9 ppb in 12 days and
levels in New York lakes declined to <.005 ppm 8 days after 4.48 kg/ha was applied . It is
contended that the dissipated diquat was merely adsorbed to hydrosoil . Diquat will
photodegrade in surface layers of water in 1-3 or more weeks when not adsorbed to particulate
matter.
AQUATIC FATE: 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.
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| Drinking Water Impact | DRINKING WATER: Diquat is rapidly oxidized by chlorine oxide above pH 8.14 and
below pH 7.12 . Similar results are observed for chlorine gas . Therefore, diquat would
disappear rapidly from chlorinated drinking water which was slightly alkaline.
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