E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Assessment Program.
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Pesticide
Information
Profile
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2,4-DB
Publication Date: 9/93
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TRADE OR OTHER NAMES
Trade names for products containing this compound include Butoxone,
Butyrac, Embutone, Embutox and Venceweed. The compound may also be found in
formulations with a host of other herbicides such as cyanazine, MCPA,
benazolin, linuron and mecoprop. It is compatible with many other
herbicides.
INTRODUCTION
2,4-DB is a selective systemic herbicide in the phenoxy family. It is
used for the control of many annual and perennial broad-leaved weeds in
alfalfa, peanuts, soybeans and other crops. In the plant the compound changes
to 2,4-D and inhibits growth at the tips of stems and roots.
This compound is not to be confused with another phenoxy compound 2,4-D
and its derivatives or with the derivatives of 2,4-DB such as the sodium salt,
the isooctyl ester or the butyl ester. Each of these are slightly different
compounds and thus would have different toxicities and environmental
characteristics. Despite the vast amount of information available on 2,4-D,
there is relatively little information on 2,4,DB. All of the material in
this profile refers to the acid form of 2,4-DB unless specifically stated
otherwise.
2,4-DB is a General Use Pesticide.
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
2,4-DB is a slightly toxic compound through oral exposure. Products
containing this compound are required to carry the signal word CAUTION on
their labels. The compound has an oral LD50 ranging between 370 mg/kg and
700 mg/kg in rats. The sodium salt has a substantially lower toxicity
(higher LD50 or 1,500 mg/kg in rats and 400 mg/kg in mice) (1). No
information was available on signs and symptoms of acute sublethal 2,4-DB
poisoning.
In rabbits the compound is only slightly toxic when exposure is through
the skin. The acute dermal LC50 of 2,4-DB is greater than 2,000 mg/kg. No
inhalation data were available.
CHRONIC TOXICITY
Short-term sub-chronic studies with dogs established a no effect level
(NOEL) at the low doses of 8 mg/kg/day. At the next highest dose tested (25
mg/kg), the dogs experienced changes in body weight and tissue effects (2).
These effects were also noted at the highest dose tested (80 mg/kg).
In a longer term chronic feeding study with rats, the NOEL was the low
dose of 3 mg/kg and the lowest dose that effects were noted (LOEL) was 30
mg/kg. The effects noted included decreases in body weight, a decrease in
heart weight and changes in blood chemistry (2).
Reproductive Effects
Female rats fed moderate doses of 75 mg/kg (compared to the LD50) of
2,4-DB, experienced a number of chronic effects including lower ovarian
weights, fewer offspring born and lower overall body weight. In addition,
numerous offspring (pups) died during lactation (2).
Teratogenic Effects
The EPA has indicated that no acceptable data are available on the
teratogenic effects of this compound (2).
Mutagenic Effects
Chromosome changes occurred due to exposure to 2,4-DB in Chinese hamster
cells, however, the exposure was relatively high (just below a threshold of
significant cell toxicity) and for relatively prolonged periods of time (17 or
more hours). Tests over two hours produced no chromosome changes (2).
Another test (the Ames test) produced no chromosomal abnormalities in
bacterial cells. The data, though minimal, indicate that the compound may
be weakly mutagenic at relatively high doses and for lengthy exposures.
Carcinogenic Effects
Preliminary evidence suggests that the compound may be weakly
carcinogenic. However, the EPA is requiring additional tests and the
submission of additional data on existing tests to further clarify the cancer
potential of the compound. The current evidence points to the
possibility of increasing carcinogenicity with increasing dose. The cancer
in the mice is associated with the liver (hepatocellular carcinomas) (2).
Another study with rats fed low doses of the compound (to 30 mg/kg/day)
caused no cancer related changes in the organisms (2).
Organ Toxicity
No data are available on the potential toxicity to organs.
Fate in Animals and Humans
Though both plants and soil microorganisms breakdown 2,4-DB to 2,4-D,
no mention of this occurring in humans or animals was found in the
literature.
ECOLOGICAL EFFECTS
2,4-DB is slightly to moderately toxic to fish. The LC50 value for the
compound in the fathead minnow is 18 mg/l, 7.5 to 17 mg/l in the bluegill
sunfish and 2 to 14 mg/l in the rainbow trout (2). No studies were available
on the toxicity of the compound to freshwater or marine invertebrates.
Several dietary feeding tests indicate that the compound is practically
non-toxic (LC50 values in excess of 5,000 mg/kg) to waterfowl and upland
game birds (2).
The compound is non-toxic to bees when used as directed (1).
Because 2,4-DB is a broadleaf herbicide, the potential exists for the
compound to be a threat to nontarget plants. However, the EPA has indicated
that an assessment of its potential threat cannot be completed until
additional information is gathered and analyzed (2).
ENVIRONMENTAL FATE
In soil, the compound is broken down by the action of soil microbes to
the product 2,4-D. The half-life for the parent compound (2,4-DB) is seven
days. 2,4-D is also a powerful herbicide though it too has a relatively short
persistence in soil (up to 50 days depending on soil type, microbial activity,
temperature and other factors) (4). 2,4-D has been detected in groundwater in
at least five states and in Canada (5). Because of the risk of groundwater
contamination from the whole family of 2,4-D related compounds, special
advisories are required on the labels of end-use products containing 2,4-D and
related products (including 2,4-DB).
There is no specific information available about the parent compound
2,4- DB in surface water or in groundwater.
In plants, the compound 2,4-DB is degraded to 2,4-D which is then
broken down further to less toxic materials. In plants tolerant to the
herbicide, the breakdown from 2,4-DB to 2,4-D is very slow (1).
Exposure Guidelines:
| NOEL: | 3 mg/kg/day |
| ADI: | 0.01 mg/kg/day (provisional) |
| HA: | NA |
| Rfd: | NA |
| TLV: | NA |
Physical Properties:
| Common name: | 2,4-DB |
| CAS #: | 94-82-6 |
| Chemical name: | 4-(2,4-dichlorophenoxy) butyric acid |
| Chemical class: | phenoxy |
| Chemical Use: | herbicide |
| Solubility in water: | 46 mg/l at 25 degrees C |
| Solubility in solvent: | Readily soluble in acetone, ethanol, diethyl ether.
Slightly soluble in benzene, toluene and kerosene. |
| Melting point: | 117-119 degrees at 25 degrees C |
| Vapor pressure: | negligible (acid and salts) |
BASIC MANUFACTURER
Rhone Poulenc Ag. Co.
P.O. Box 12014
2 T.W. Alexander Drive
Research Triangle Park, NC 27609
Telephone: 919-549-2000
FAX: 919-549-4689
Review by Basic Manufacturer:
Comments solicited: June, 1993
Comments received:
REFERENCES
The Agrochemicals Handbook. 1991. The Royal Society of Chemistry.
Cambridge, England.
Walker, Mary M. and L.H. Keith. 1992. EPA's Pesticide Fact Sheet
Data Base. Lewis Publishers. Chelsea, MI.
The Farm Chemicals Handbook. 1992. Meister Publishing.
Willoughby, OH.
National Research Council Canada. 1978. Phenoxy Herbicides --Their
Effects on Environmental Quality with Accompanying Scientific Criteria
for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD). Subcommittee on
Pesticides and Related Compounds, NRC Associate Committee on Scientific
Criteria for Environmental Quality, Ottawa, Canada.
Howard, Philip H. 1991. Handbook of Environmental Fate and Exposure
Data for Organic Chemicals. Lewis Publishers. Chelsea, MI.
Disclaimer: Please read
the pesticide label prior to use. The information contained at this web
site is not a substitute for a pesticide label. Trade names used herein
are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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