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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.

  Pesticide
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Profile
2,4-DB

Publication Date: 9/93

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

  1. The Agrochemicals Handbook. 1991. The Royal Society of Chemistry. Cambridge, England.
  2. Walker, Mary M. and L.H. Keith. 1992. EPA's Pesticide Fact Sheet Data Base. Lewis Publishers. Chelsea, MI.
  3. The Farm Chemicals Handbook. 1992. Meister Publishing. Willoughby, OH.
  4. 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.
  5. Howard, Philip H. 1991. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Lewis Publishers. Chelsea, MI.