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Acifluorfen

Publication Date: 9/93

TRADE OR OTHER NAMES

Acifluorfen is found in several Blazer products. Other trade names include Carbofuorfen, RH-6201 (sodium acifluorfen), and Tackle. This herbicide is compatible with other pesticides though its toxicity to crops may increase.

INTRODUCTION

Acifluorfen is a contact diphenolic ether herbicide used to control broadleaf weeds and grasses in soybeans, peanuts, peas, and rice It can be applied before or after crop emergence. It is especially effective against cocklebur, velvetleaf, common lambsquarters, morning glory, and jimsonweed. Acifluorfen selectively controls broadleaf weeds when applied after soybeans have emerged (6). The activity of this compound is enhanced by sunlight. Acifluorfen may be toxic to some crops plant such as soybeans if mixed with fertilizers.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Acifluorfen is very toxic and is labeled with a DANGER signal word due to its potential to cause serious eye injury. Other effects occur only at higher doses. Symptoms of acute exposure to acifluorfen are not recorded for humans. The oral LD50 of acifluorfen in male albino rats is 1,300 mg/kg (7). In rabbits, the dermal LD50 of Blazer is 450 mg/kg, while it is 2,000 mg/kg for Tackle (2).

CHRONIC TOXICITY

In animals, acifluorfen adversely affects development and liver and kidney weights. Research indicates that it is not mutagenic. Studies on reproductive effects are inconclusive.

Reproductive Effects

No adverse effects were observed in rodent parents or their offspring when the parents were fed daily doses well below lethal levels. Body weights, food consumption, fertility, and pregnancy were comparable in both treated and untreated animals (2).

However, in another rat study, at higher doses, both parents and offspring suffered kidney lesions and death. This suggests that levels high enough to cause toxicity in the mother are needed to affect reproduction (2).

Teratogenic Effects

In one study, rats were given high doses of sodium acifluorfen through a stomach tube during the critical periods of pregnancy. At these doses, body weights of the fetuses were lower, and bone development was delayed (2).

Mutagenic Effects

Various mutagenesis assays of acifluorfen products indicate that this pesticide does not cause mutations. These include studies of both bacteria and cells from mammals (2).

Carcinogenic Effects

Some studies show acifluorfen to be carcinogenic, while others do not; the main differences among the studies were the dose levels administered and the lengths of the studies. One study of mice fed high doses for 18 months showed decreases in body weight and increases in both benign and malignant liver tumors (2). As a result, acifluorfen is classified as a probable human carcinogen by the U.S. Environmental Protection Agency (8).

Organ Toxicity

In addition to being a skin and eye irritant, acifluorfen affects the weight and functions of the liver, heart, and kidneys at high doses.

Male and female rats fed high daily doses for four weeks showed decreased food consumption and increased liver and kidney weights (2). In a one-year study of rats fed lower doses, both sexes experienced decreased body weight and increased liver weight (2).

In a two year study, beagle dogs were fed high daily doses of acifluorfen. Irregular heart rhythms were noted in some of the animals. In addition, there were some blood changes and an increase in liver and kidney weights (2).

ECOLOGICAL EFFECTS

Aciflurofen is slightly toxic to fish. The LC50 values for the compound range from 31 mg/l for bluegill to 54 mg/l for rainbow trout. The compound is also only slightly toxic to mallards and is moserately toxic to bobwhite quail. It is non-toxic to bees. No information on bioaccumulation was found.

ENVIRONMENTAL FATE

Acifluorfen is a moderately persistent, selective herbicide. Light, temperature, and relative humidity influence acifluorfen activity.

In susceptible plants, such as common cocklebur and ragweed, the compound is absorbed through the leaves and roots and is translocated only slightly. Maximum herbicide action occurs three to seven days after it is applied (1). The herbicide works by inhibiting a critical plant enzyme. In acifluorfen-resistant plants like soybeans, no acifluorfen movement from the treated leaves takes place. These plants can metabolize acifluorfen into a non-toxic form (4). High relative humidity favors herbicide penetration in the plant. High temperatures before and after spraying tend to increase weed susceptibility and death (3).

Acifluorfen usually lasts from four to six weeks in the soil. In one study, acifluorfen applied to a silt loam degraded with a half-life of 59 days. Microbial action accounts for the majority of the compounds loss from soil. No leaching of the chemical below three inches was observed (2). Acifluorfen was looked for, but not found, in a number of wells throughout the United States.

Acifluorfen is rather stable in water; no degradation was observed in laboratory studies lasting up to 28 days (2). However, when it is exposed to sunlight in the water, it degrades quickly. The half-life under continuous light was 92 hours in water (2). When it does degrade, the primary breakdown product tends to vaporize (2). Because of its sensitivity to light, this chemical has an atmospheric half-life of about 4.5 days. It evaporates from the soil surface.

PHYSICAL PROPERTIES AND GUIDELINES

In its physical state at 25 degrees C, acifluorfen is most often an off-white solid as an acid, or a white powder or brown crystalline powder as a sodium salt. It should not be mixed with oils, surfactants, liquid fertilizers, and other pesticides. It is a member of the phenolether chemical family. Its chemical name is sodium 5-[2-chloro-4- (trifluoro-methyl)phenoxy]-2-nitrobenzoate.

Physical Properties:

CAS #: 62476-59-9 (sodium salt); 5094-66-6 (white solid)
Solubility in water: >25g/100g
Melting point: 124-125 degrees C (white powder); 151.5-157 degrees C (acid) (2)
K(ow): -4.85 (acid; calculated) (2)

Exposure Guidelines:

NOEL: 1.25 mg/kg/day (2)
ADI: 0.0125 mg/kg/day (2)
Drinking water health advisory:
Drinking Water Equivalent Level (DWEL): 0.427 mg/L (2)

BASIC MANUFACTURER

BASF Corp.
Agr. Prod. Group
P.O. Box 13528
Research Triangle Park, NC 27709-3528
Telephone: 919-361-5722

Review by Basic Manufacturer:

Comments solicited: November, 1992
Comments received:

REFERENCES

  1. Johnson, W.O.; Kollman, G.E.; Swithenbank, C; and Yih, R.Y. 1978. RH-6201 (Blazer): A new broad spectrum herbicide for postemergence use in soybeans. J. Agric. Food Chem. 26 (1): 285-286.
  2. U.S. Environmental Protection Agency, Office of Drinking Water. "Acifluorfen Health Advisory." Draft Report. August 1987.
  3. Ritter, R.L. and Coble, H.D. 1981. Influence of temperature and relative humidity on the activity of acifluorfen. Weed Science. 29: 480-485.
  4. 1981. Penetration, translocation, and metabolism of acifluorfen in soybean, common ragweed, and common cocklebur. Weed Science. 29: 474- 480.
  5. "SAP Makes Draft Recommendations on Two of Eight Pesticides." Pesticide and Toxic Chemical News, 16 December 1987, p. 32.
  6. Wills, G.D. and McWhorter, C.G. 1981. Effect of environment on the translocation and toxicity of acifluorfen to showy crotalaria. Weed Science. 29: 397-408.
  7. Windholz, M. et al., eds. The Merck Index. 10th edition. p.16, Rahway, N.J.: Merck & Co. Inc., 1983.
  8. Quest, John A., Whang Phang, Karen L. Hamernik, Marcia van Gemert, Bernice Fisher, Richard Levy, Theodore M. Farber, William L. Burnam, and Reto Engler. 1989. Evaluation of the Carcinogenic Potential of Pesticides, 1. Acifluorfen. Regulatory Toxicology and Pharmacology 10: 149-159. /OL>