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Carboxin

Publication Date: 9/93

TRADE OR OTHER NAMES

Trade names for products containing carboxin include Cadan, Padan, Sanvex, Thiobel, and Vegetox. It is very often used in combination with other fungicides such as thiram or captan.

INTRODUCTION

Carboxin is a systemic anilide fungicide. It is used as a seed treatment for control of smut, rot, and blight on barley, oats, rice, cotton, vegetables, corn and wheat. It is also used to control fairy rings on turf grass. The product may be used to prevent the formation of these diseases or may be used to cure existing plant diseases (9).

Carboxin is a general use pesticide.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Carboxin is a slightly toxic compound and carries the signal word CAUTION on the label. Symptoms of acute poisoning can include vomiting and headache. Recovery is very rapid if the exposed individual is treated quickly. One study reported a rat oral LD50 of 430 mg/kg (4). Since chronic studies have been successfully completed at doses higher than this, the LD50 of 3,820 mg/kg which was reported in another study seems more reasonable (5) and is consistent with the oral LD50 of 3,550 mg/kg in mice (2).

The compound produces very little skin irritation, however it can seriously irritate the eyes. Rabbits which had been exposed to carboxin on their skin for three weeks showed no irritation.

CHRONIC TOXICITY

A 28-day study with rats fed doses up to 311 mg/kg showed some fluid accumulation in the liver even at low doses (2). Another rat study showed kidney changes at somewhat higher doses (1,000 mg/kg) fed for 90 days (2). A two-year rat study with levels of up to 30 mg/kg produced no compound-related effects in terms of physical appearance, behavior, blood chemistry, or urinalysis (2). However, there were changes in organ weights.

Male and female mice also showed liver effects after being fed high doses (912 mg/kg) of carboxin for a year and a half (2). Beagle dogs showed no effects at the highest dose tested, 15 mg/kg for two years (2). Carboxin has an unusually broad range between the maximum tolerated dose and the dosage that produces no effects.

Reproductive Effects

A three-generation study with rats showed treatment-related effects on reproductive performance at levels from 5 to 30 mg/kg/day. However, at the highest dose, there was only moderate growth suppression in nursing pups (2). It is unlikely that the compound would produce any reproductive effects in humans at expected exposure levels.

Teratogenic Effects

At the highest dose tested, 40 mg/kg administered to pregnant rats on days 6 through 15, there were no birth defects in the offspring (2). Pregnant rabbits treated with very high doses on days 6 through 27 of gestation had increased abortions but no fetal malformations (2).

Mutagenic Effects

Carboxin is either a non-mutagen or is a very weak mutagen based on information from several studies on bacteria and mammalian cells.

Carcinogenic Effects

A two-year study with rats fed up to 30 mg/kg/day showed no evidence of increased tumor frequency (2). Another two-year study at levels up to 3,000 ppm (approximately 180 mg/kg/day), had similar results (5).

Mice fed up to 900 mg/kg for 84 weeks had no apparent compound- related increase in tumor formation. It is not likely that carboxin would cause cancer in humans.

Organ Toxicity

In an adolescent human, ingestion of carboxin treated seeds resulted in headache and vomiting within one hour, with the patient recovering quickly (within two hours). There was no mention of the ingested dose (10).

Fate in Humans and Animals

Rats excreted almost all of a carboxin dose in 24 hours, with most excreted in urine and some in feces (5). Rabbits showed a similar excretion pattern. Carboxin is incompletely absorbed in the gut, especially in rats (2). The compound does not acumulate in animal tissues. The main breakdown product is carboxin sulfoxide for which the rat oral LD50 is 2,000 mg/kg. Carboxin sulfoxide is sold as a pesticide also and is known as oxycarboxin (5).

Only trace amounts of carboxin were found in rat tissues 48 hours after dosing (2). In milk cows fed up to 5 ppm for 10 days, less than 2% of the administered dose was found in tissues. However, significant levels were found in milk a few days after exposure.

ECOLOGICAL EFFECTS

The oral LD50 in chickens is very high at 24 grams/kg indicating that it has a very low acute toxicity (1). In chronic, low exposure experiments of 5.5 months, changes were noted in the digestive tract, cardiovascular system and blood of chickens (3).

Carboxin is highly toxic to fish. The 96-hour LC50 for rainbow trout was greater than 0.1 mg/l (1), however the specific values were not given. Carboxin is practically non-toxic to freshwater invertebrates. Juvenile crayfish in a similar test had a 217 mg/l LC50 (3). The compound is non-toxic to bees.

ENVIRONMENTAL FATE

Carboxin is rapidly degraded to carboxin sulfoxide in soil. In one study, after seven days, 95% of the parent was gone and the sulfoxide, a breakdown product, represented 31 to 45% of the amount applied. Minor products formed were carboxin sulfone, hydroxy carboxin and CO2. Carboxin does not readily adsorb to soil. Both parent and sulfoxide are very mobile and could possibly leach to groundwater (2).

In water, carboxin oxidizes to the sulfoxide and sulfone within seven days (2). This happens both under ultraviolet light and in the dark (5). Blue-green algae like Anabaena and Nostoc degrade the pesticide extensively. Other algae can also break down carboxin, but not to the same extent (1).

Although the distribution pattern of the parent and sulfoxide metabolite vary, carboxin is found systemically (throughout the plant) in all species of plants studied (5). Plants grown from treated seed had no carboxin present six weeks after emergence. Carboxin sulfoxide found in plants can come either from the soil or through oxidation within the plant.

Exposure Guidelines:

NOEL (rats): 10 mg/kg/day
HA: 0.7 mg/l (lifetime)
RfD: 0.1 mg/kg/day
LEL: 30 mg/kg/day
DWEL: 4 mg/l

Physical Properties:

CAS #: 5234-68-4
Chemical Name: 5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carbamil
Chemical class/use: carboxanilide fungicide
Solubility in water: 195 mg/l at 25 degrees C
Solubility in other solvents: acetone 600 g/kg; benzene 150 g/kg; methanol 210 g/kg
Melting Point: 93-95 degrees C
Vapor Pressure: 11.8 x 10 to the minus 7 power mm Hg
Absorption Coefficient: 260 ml/gram

BASIC MANUFACTURER

Uniroyal Crop Protection Div
World Headquarters
Middlebury, CT 06749
Telephone: 203/573-2000
Emergency: 203/723-3670

Review by Basic Manufacturer:

Comments solicited: November, 1992
Comments received:

REFERENCES

  1. National Library of Medicine (1992). Hazardous Substances Databank. TOXNET, Medlars Management Section, Bethesda, MD.
  2. U.S. Environmental Protection Agency (1987). Health Advisory, Office of Drinking Water.
  3. U.S. Environmental Protection Agency (1968-81). Pesticide Abstracts, Office of Pesticides and Toxic Substances, Management Support Division, 79-0210, 81-3526.
  4. National Institute for Occupational Safety and Health (1983 Supplement) Registry of Toxic Effects of Chemical Substances, U.S. Dept of Health and Human Services, Public Health Service, Centers for Disease Control, Cincinnati, OH.
  5. Food and Drug Administration (1986). The FDA Surveillance Index. Bureau of Foods, Dept of Commerce, National Technical Information Service, Springfield, VA.
  6. Occupational Health Services, Inc. (1988). Hazardline, New York, NY.
  7. Hartley, D., and H. Kidd, Editors (1986). The Agrochemicals Handbook. The Royal Society of Chemistry, The University, Nottingham, England.
  8. Chin, Wei-Tsung, G. M. Stone and A. E. Smith (1970). Metabolism of Carboxin (Vitavax) by Barley and Wheat Plants, J Agric Food Chem 18(4):709-712.
  9. Ware, George W. (1986). Fundamentals of Pesticides, A Self Instruction Guide. ThomsonPublications, Fresno, Ca.
  10. U.S. Environmental Protection Agency (1987). Carboxin. Health Advisory. Office of Drinking Water.