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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.


Publication Date: 9/93


The trade names and synonyms for chloramben are Ambiben, Amiben, Amiben DS, Chlorambene, Ornamental Weeder, and Vegiben. The compound may be used in combination with a wide range of other pesticides.


Chloramben is a selective, preemergence benzoic acid herbicide that is primarily soil-applied to control annual grass and broadleaved weed seedlings. It is mostly used for soybeans, but it is also used for dry beans, peanuts, sunflowers, peppers, cotton, sweet potatoes, squash, hardwood trees, shrubs, and some conifers. Chloramben inhibits seedling root development and causes plants to bend and die as they emerge from the soil.

Chloramben's use is not restricted by the United States Environmental Protection Agency.



Moderately toxic, chloramben is labeled with a CAUTION signal word. The major health concern for humans is dermatitis resulting from skin exposure to the pesticide.

The oral LD50 for rats is 3,500 mg/kg (1, 5) and 3,725 mg/kg for mice. This suggests it would be fatal to humans only if ingested in very large amounts.

The dermal LD50 for rabbits is 3,136 mg/kg (5) for albino rats, it is greater than 3,160 mg/kg. This indicates that chloramben has about the same toxicity when applied to the skin as when ingested.


Chloramben has not been shown to affect reproduction, but it does affect the development of the fetus in some animals. Studies indicate that chloramben is not a mutagen. This chemical's carcinogenic status has not been determined. Chloramben exposure can be irritating to mammals, but it is not known to be toxic to any organs. Animals rapidly excrete chloramben.

Reproductive Effects

No effects on fertility, survival of the fetus, or on nursing ability were found in a long-term study of rats fed large daily doses of chloramben (4).

Teratogenic Effects

When pregnant rabbits were given high doses of chloramben during the sensitive period of gestation, no developmental defects were seen in the fetuses. Pregnant rats fed lower doses of chloramben during the sensitive period of gestation were not affected, but fetal deaths increased and fetal skeletal development was not complete. At even lower doses, no increase in fetal deaths were seen, but the bones were not fully developed. No changes were seen at the lowest doses (4).

Mutagenic Effects

Most bacterial and mammalian cell assays of chloramben indicate that it is not toxic to genetic material. However, mutagenicity was seen in one test using Chinese hamster ovary cells (4).

Carcinogenic Effects

The carcinogenic status of chloramben has not been established by the Environmental Protection Agency (3).

Rats given high daily doses of chloramben for 80 weeks did not show carcinogenicity. But mice given similar doses (up to 300 mg/kg) each day for 80 weeks developed cancerous tumors (2, 3).

Organ Toxicity

Chloramben irritates the throat, lungs, skin and the eyes. However, chloramben is not known to move through the skin. On rats, a low dose skin application caused mild irritation that subsided within 24 hours (2).

In long-term tests on rats, mice and dogs, no chloramben-related effects on body weight, body function, and organs were observed even at very high concentrations (1, 4, 6).

Fate in Humans and Animals

Several animal studies have shown that once ingested, chloramben is rapidly excreted in the urine and feces with no residues found in tissues. For instance, very small amounts of chloramben fed daily to lactating cows left the body via urine (88%) and the feces (5%) within four days. No residues were found in the milk (2). Similarly, dogs fed very small amounts showed rapid chloramben excretion, with no residues found in the tissues (2).

Chloramben is quickly absorbed from the gastrointestinal tract of female rats. About 97% of an oral dose is absorbed and then excreted through the urine and expired air. In rats fed a single dose, 70% of that recovered 24 hours later from the urine was the original compound. Only 0.6% of the dose remained in the body after three to four days (4).


Chloramben has a low toxicity to wildlife, including wild birds and both cold-water and warm-water fish. For example the LC50 of chloramben is 4,640 in mallard ducks indicating that the compound is practically non-toxic to this species (8). Chloramben is also not toxic to bees (8, 9).


When soil-applied, plant roots are the primary site of absorption and chloramben action. Roots of resistant species, like soybeans, can absorb large amounts of the compound, but translocate very little of it to the above-ground portions of the plant. In contrast, the susceptible barley plant translocates a significant amount into its leaves, and thus dies.

In plants, chloramben quickly changes from its free, unstable form into a more stable compound which accumulates in both susceptible and tolerant plants. Chloramben reacts with plant constituents to form a stable and non-toxic product. The ease of formation of this metabolite seems to be the reason the herbicide is not totally degraded within the plant.

Chloramben is active in the soil. The wetter the soil, the greater the toxicity of this compound to target plants. Rainfall or irrigation within 10 to 14 days of application is needed for chloramben to be effective against weeds.

In a soil solution, chloramben formulations readily break down into forms which are less attracted to soil and are thus quite mobile in the soil (7). Thus, much of it is lost from the soil due to leaching although some loss is due to breakdown by soil microorganisms. Leaching is greatest in sandy soil (2). As the organic matter content of the soil increases, binding of chloramben also increases and leaching decreases. Like most preemergence herbicides, the activity is nearly the same on muck soils as on mineral soils. In general, chloramben activity lasts for about six to eight weeks in soil (8). Chloramben readily degrades in water exposed to sunlight (4). Of 188 groundwater samples, chloramben was found in only one, at a maximum concentration of 1.7 ug/l (ppb) (4). The compound does not evaporate appreciably.


Chloramben is a 2,3,5-substituted (with chlorine atoms) benzoic acid. It is a colorless and odorless crystalline solid.

Exposure Guidelines:

NOEL: 1.75 mg/L(4)
ADI: 0.25 mg/kg/day(4)
Drinking water
health advisory:
Drinking Water Equivalent Level (DWEL): 0.525 mg/L(4)

Physical Properties:

CAS #: 133-90-4
Solubility in water: 799 mg/L at 25 degrees C (6)
Solubility in solvents: soluble in alcohol, alkali, ether, acetone (23.27g/100g at 29 degrees C (1), and ethanol 17.3g/100ml at 25 degrees C.
Melting point: 200-201 degrees C.
Vapor pressure: 0.007 torr at 100 degrees C (6)
Koc: 13


Rhone Poulenc*
P.O. Box 12014
2 T.W. Alexander Dr.
Research Triangle Park, NC 27709
Telephone: 919-549-2000

*Chloramben is no longer produced or sold by Rhone Poulenc (or by anyone else) in the United States.

Review by Basic Manufacturer:

Comments solicited: October, 1992
Comments received:


  1. Herbicide Handbook. 4th ed. 1979. p. 99. Weed Science Society of America.
  2. National Library of Medicine. (1992) Hazardous Substances Databank. Chloramben.
  3. Occupational Health Services. Material Safety Data Sheet on Chloramben. 4/2/87. NY.
  4. U.S. Environmental Protection Agency. Office of Drinking Water. "Chloramben Health Advisory." Draft Report. August 1987.
  5. Windholz, M., et al., eds. 1983. The Merck Index. 10th ed. Merck & Co, Inc, Rahway, NJ.
  6. Worthing, C.R., and Walker, S.B., eds. 1987. "Chloramben." The Pesticide Manual. 8th ed. p. 142. The British Crop Protection Council.
  7. Johnson, W.W., and Finley, M.T. 1980. Handbook of Acute Toxicity of Chemicals to Fish and Wildlife. NPMP(DOI/FW) Resource Publication No. 137.
  8. The Agrochemicals Handbook.
  9. The Royal Society of Chemistry. Cambridge, England.
  10. The Farm Chemicals Handbook. (1992). Meister Publishing. Willoughby, OH.