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Chlorothalonil

Publication Date: 5/94

TRADE OR OTHER NAMES

Trade names include Bravo, Chloro-thalonil, Daconil 2787, Exotherm Termil, Forturf, Mold-Ex, Nopcocide N-96, Ole, Pillarich, Repulse, and Tuffcide. The compound can be found in formulations with many other pesticide compounds.

REGULATORY STATUS

Chlorothalonil is classified as a General Use Pesticide (GUP) by the U.S. Environmental Protection Agency.

INTRODUCTION

Chlorothalonil is a broad-spectrum organochlorine pesticide (fungicide) used to control fungi that threaten vegetables, trees, small fruits, turf, ornamentals, and other agricultural crops. It also controls fruit rots in cranberry bogs, and is used in paints.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Chlorothalonil is slightly toxic to mammals, but it can cause severe eye and skin irritation in certain formulations (13). Chlorothalonil containing products have a range of signal words, including: WARNING (Bravo 720, 500), CAUTION (Exotherm Termil), and DANGER (Bravo W-75, Daconil W-75). Each of these products has a different formulation and product concentration and thus requires a different signal word. Very high doses may cause a loss of muscle coordination, rapid breathing, nose bleeding, vomiting, and hyperactivity. Dermatitis, vaginal bleeding, bright yellow and/or bloody urine, and kidney tumors may also occur, followed by death (4).

The oral LD50 is > 10,000 mg/kg for rats (13), and 6,000 mg/kg for mice (7). The acute dermal LD50 for both albino rabbits and albino rats is 10,000 mg/kg (6). In albino rabbits, 3 mg of chlorothalonil applied to the eyes caused mild irritation that subsided within seven days of exposure (8).

CHRONIC TOXICITY

In a number of tests of varying lengths of time, rats which were fed a range of doses of chlorothalonil generally showed no effects on physical appearance, behavior, or survival. Kidney changes such as kidney enlargement were common (8). In a two-year dietary rat study, the lowest dose of chlorothalonil that produced no adverse effects in the animals was 60 ppm (3 mg/kg) (15).

Human eye and skin irritation is linked to chlorothalonil exposure. Fourteen out of 20 workers exposed to 0.5% chlorothalonil in a wood preservative developed dermatitis. All workers showed swelling and inflammation of the upper eyelids (8). Allergic skin responses have also been noted in vegetable and in horticultural workers (12).

Reproductive Effects

In a long-term rat study, high doses fed to both males and females did not affect reproduction or the litters that were produced. However, body weight gains for males and females of each generation were decreased (8).

Administration of high doses of chlorothalonil to pregnant rabbits through the stomach during the sensitive period of gestation resulted in four of the nine mothers aborting (8). These studies suggest that chlorothalonil will not affect human reproduction except at very high doses.

Teratogenic Effects

Female rats given high doses of chlorothalonil through the stomach during the sensitive period of gestation had normal fetuses, even though that dose was toxic to the mothers (8). One study of birth defects in rabbits showed no effects (5). Thus, chlorothalonil is expected to produce no birth defects in humans.

Mutagenic Effects

Mutagenicity studies on various animals, bacteria, and plants indicate that chlorothalonil does not cause any chromosomal changes (3, 5, 8). The compound is therefore not expected to pose mutagenic risks to humans.

Carcinogenic Effects

Chlorothalonil is a potential human carcinogen, known to affect the kidney, ureter, and bladder in experimental animals (7). Male and female rats fed chlorothalonil daily over a lifetime developed carcinogenic and benign kidney tumors at the higher doses (8). In another study, where mice were fed high daily doses of chlorothalonil for two years, females developed tumors in the fore-stomach area (attributed to irritation by the compound) and males developed carcinogenic and benign kidney tumors (8). However, this latter study was inconclusive as to the relationship between dose of chlorothalonil and the presence of cancer in the test animals.

Organ Toxicity

Chronic studies of rats and dogs fed high dietary levels show that chlorothalonil is toxic to the kidney. In addition to less urine output, changes in the kidney included enlargement, greenish-brown color, and development of small grains (9).

Skin contact with chlorothalonil may result in dermatitis or light sensitivity (12).

Fate in Humans and Animals

Chlorothalonil is rapidly excreted, primarily unchanged, from the body. It is not thought to be stored in animal tissues. Rats and dogs fed very high doses for two years eliminated almost all of the chemical in urine, feces, and expired air. After two years, the amount of the breakdown product found in the liver tissues was considered insignificant in both dogs and rats (8). At lower concentrations, chlorothalonil leaves the body within 24 hours. Residues have not been found in the tissues or milk of dairy cows (9).

ECOLOGICAL EFFECTS

Effects on Birds

Chlorothalonil is practically non-toxic to birds. The LD50 in mallard ducks is nearly 5000 mg/kg (6). Most avian wildlife are not significantly affected by this compound (13).

Effects on Aquatic Organisms

Chlorothalonil and its metabolites are highly toxic to fish, aquatic invertebrates, and marine organisms. Fish, such as rainbow trout (LC50 of 0.25 mg/l), bluegills (LC50 of 0.3 mg/l) and channel catfish (LC50 of 0.43 mg/l) are noticeably affected even when chlorothalonil levels are low (less than 1 ppm).

Chlorothalonil is not very water soluble, does not store in fatty tissues and is rapidly excreted from the body. Its bioaccumulation factor is quite low, about 425 times the background water concentration.

Effects on Other Organisms (Nontarget species)

The compound is non-toxic to bees (14).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

In aerobic soils, the half-life for chlorothalonil is from one to three months. Increased soil moisture or temperature increases chlorothalonil degradation. It is not degraded by sunlight on the soil surface (6).

Chlorothalonil has high binding and low mobility in silty loam and silty clay loam soils, and has low binding and moderate mobility in sand. In studies conducted in water over ten weeks time, chlorothalonil, at low levels, was generally stable (8).

Chlorothalonil was not found in any of 560 groundwater samples collected from 556 sites (8).

Breakdown of Chemical in SurfaceWater

In very basic water (pH 9.0), about 65% of the chlorothalonil was degraded into two major metabolites after ten weeks (8). Chlorothalonil was reported to be found in one surface water location in Michigan at 6.5 mg/L (8).

Breakdown of Chemical in Vegetation

Chlorothalonil's residues may remain on above-ground crops at harvest, but will dissipate over time. Chlorothalonil is a fairly persistent fungicide on plants, depending on the rate of application. Small amounts of one metabolite are found in harvested crops (9).

PHYSICAL PROPERTIES AND GUIDELINES

Chlorothalonil is an aromatic halogen compound, a member of the chloronitrile chemical family. It is a grayish to colorless crystalline solid which is odorless to slightly pungent. It is non-corrosive and stable in moderately alkaline or acidic aqueous solutions. Chlorothalonil's molecular weight is 265.89 g/mol. At high temperatures, this pesticide may decompose to emit hydrochloric acid.

Exposure Guidelines:

RfD: 0.015 mg/kg
HA: 0.5 mg/l
ADI: 0.015 mg/kg (8)
PEL: N/A

Physical Properties:

CAS #: 1897-45-6
Chemical name: tetrachloroisophthalonitrile
Solubility in water: 0.6 mg/l @ 25 degrees C (5) (Considered insoluble).
Solubility in solvents: Soluble in acetone, butanone, dimethyl formamide, and dimethyl sulfoxide (20 g/kg); cyclohexanone (30 g/kg); kerosene (< 10g/kg); xylene (80 g/kg); methyl ethyl ketone; mineral seal oil (ALL @ 25 degrees C) (6).
Melting point: 250-251 degrees C (10)
Boiling point: 350 degrees C (4)
Vapor pressure: 1.3 Pa @ 40 degrees C (10)
Partition Coefficient (octanol/water) (log): 1.32 (calculated (2, 8, 11))
Adsorption Coefficient: 1,300 - 14,000 (calculated (1, 2))
Chemical Class/use: organochlorine/fungicide

BASIC MANUFACTURER

ISK Biotech Corporation
5966 Heisley Road
P.O. Box 8000
Mentor, OH 44061-8000
Telephone: (216) 357-4100

Review by Basic Manufacturer:

Comments solicited: October, 1992
Comments received: December, 1993

REFERENCES

  1. Hunter, R., et al. 1984. User Manual for the QSAR system. Center for Data Systems and Analysis. Montana State University.
  2. Leo, A. 1978. Report on the calculation of octanol/water log P values for structures in the EPA files. Claremont, CA.
  3. National Library of Medicine. 1992. Hazardous Substances Databank. Chlorothalonil. 13 February 1992.
  4. Occupational Health Services Inc. 1987. Material Safety Data Sheet: Chlorothalonil. 2/25/87. NY.
  5. "Pesticide Tolerance for Chlorothalonil." Federal Register, 27 June 1985, 40 CFR Part 180.
  6. Worthing, C.R., ed. 1983. The Pesticide Manual: Seventh Edition. The British Crop Protection Council, Croydon, England.
  7. Sweet, D.V., ed. 1987. Registry of Toxic Effects of Chemical Substances Microfiche January 1987. NIOSH, Washington, DC.
  8. U.S. Environmental Protection Agency. 1987. Office of Drinking Water. "Chlorothalonil Health Advisory." Draft Report. August 1987.
  9. Vettorazzi, G. 1979. International Regulatory Aspects for Pesticide Chemicals. CRC Press. Boca Raton, FL.
  10. Windholz, M., et al., eds. 1983. Chlorothalonil. The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. 10th Edition. Merck & Co., Inc., Rahway, NJ.
  11. Woodard, R. 1985. Interagency Delta Health Aspects Monitoring Program, Project Report. California Department of Water Resources.
  12. Edwards, I. R., D. G. Ferry, and W. A. Temple. 1991. Fungicides and Related Compounds. in Handbook of Pesticide Toxicology, Volume 3: Classes of Pesticides. Wayland J. Hayes, Jr. and Edward R. Laws, Jr., eds. Academic Press, Inc., New York, NY.
  13. Walker, M. M. and L. H. Keith. 1992. U.S. Environmental Protection Agency's Pesticide Fact Sheet Database. Lewis Publishers, Chelsea, MI.
  14. The Agrochemicals Handbook: Third Edition. 1991. The Royal Society of Chemistry, Unwin Brothers Ltd., Surrey, England.
  15. U.S. Environmental Protection Agency. 1984. Chlorothalonil: Fact Sheet Number 36. September 30, 1984. Washington, DC.