Triadimefon
TRADE OR OTHER NAMES
Trade names for products containing triadimefon include Amiral, Bay MEB 6447, and Bayleton. The compound may also be found in formulations with other fungicides such as captan, carbendazim, folpet, dodine, and propineb (1).
REGULATORY STATUS
Triadimefon is a General Use Pesticide (GUP).
INTRODUCTION
Triadimefon is also known as Bayleton. It is a systemic fungicide in the triazole family of chemicals. Triadimefon is used to control powdery mildews, rusts and other fungal pests on cereals, fruits vegetables, turf, shrubs and trees.
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Triadimefon is a moderately toxic compound that carries the signal word WARNING on its label. While there is a rather extensive amount of information on the acute toxicity of the compound to certain animals, there is very little information about its direct effects on humans.
The technical compound Bayleton (92.6% triadimefon) has an acute oral LD50 in rats of 569 mg/kg, around 1,000 mg/kg in mice, and about 500 mg/kg in rabbits and dogs (1). These rather consistent values are slightly higher than normal for the classification moderately toxic. The compound is given the stronger classification because of its potential to cause adverse chronic effects at low to moderate dose levels. As expected, the lower potency formulations of Bayleton have lower toxicities (higher LD50 values).
Acute inhalation toxicity of the compound is rather low. The inhalation LC50 is greater than 291 mg/m3 for rats and near that amount for mice exposed over a four-hour interval (1). Acute toxicity through exposure to the skin is also fairly low. The LD50 values for the dermal toxicity of Bayleton (technical) are greater than 1,000 mg/kg for rats and 2,000 mg/kg for rabbits (2).
There was no information about the signs or symptoms of acute toxicity.
CHRONIC TOXICITY
While there are a number of studies on the chronic toxicity of the compound to a variety of different species, the main concern is its potential to cause birth defects.
A number of two year studies have indicated that there are several toxic responses to low to moderate doses of the compound. Dogs fed triadimefon over a range of doses exhibited a reduction in body weight, a decrease in enzyme activity, and an increase in cholesterol levels at the highest doses tested (2).
Reproductive Effects
Female rats fed up to 90 mg/kg of Bayleton over three generations showed a number of adverse effects. No effects were noted in the fetuses at the maternal doses below 2.5 mg/kg. At the middle doses tested (around 15 mg/kg) the second generation offspring experienced a decrease in weight gain. At the highest dose, the females experienced a reduction in body weight and a decrease in fertility (2). In another study conducted over only two generations, the female rats experienced decreases in their ovary weights at the 2.5 mg/kg dose (2). At 90 mg/kg there were reductions in litter size and reduced viability of the offspring combined with lower birth weights for the second generation offspring (2). The evidence suggests that there is some potential for compound induced effects in humans though only at moderate to high levels of exposure over time.
Teratogenic Effects
Bayleton's teratogenic potential is relatively low (3). The concentrations of Bayleton that caused birth defects in rats were high enough to also produce maternal toxicity. Cleft palates were noted in the offspring of female rats fed moderate doses of 75 mg/kg (length of time was not noted). In another study, no teratogenic effects were noted in the offspring of female rats fed 50 mg/kg of Bayleton in the form of an emulsion. In another teratogenic study, rib deformities were noted in offspring when female mother rats were fed the high dose of 90 mg/kg (2).
In response to the compound's potential to produce teratogenic effects in rats and thus a possibility in pregnant female workers, a study of the exposure levels of pesticide workers to the compound was conducted. The study showed that the highest dermal and inhalation level of exposure for workers was around 60 ug which adds up to approximately 0.008 mg/kg/8-hrs for a 70 kg worker, which is a value considerably lower than the 10 mg/kg that caused teratogenic effects in test animals (3). Thus, Bayleton's potential to present a risk of human birth defects is minimal.
Mutagenic Effects
Six separate studies indicate that the Bayleton compound is non- mutagenic. Several other tests were inconclusive (2). It is unlikely that the compound poses a significant mutagenic risk to humans.
Carcinogenic Effects
Two out of three studies on Bayleton's potential to cause cancer were negative. The highest dose tested in the two negative studies was 250 mg/kg. This dose produced a significant decrease in body weight gain and a decrease in the red blood cell count and 'violent motor reactions' in the exposed rats. There was also considerable illness and eventually death at this relatively high dose. Thus, the study does not adequately conform to the EPA guidelines for carcinogenicity testing. In the other negative study, mice were fed moderate doses (90 mg/kg) of Bayleton (technical). While the test animals experienced decreased body weight gain and a reduction in red blood cell count and other symptoms of chronic toxicity, no cancer was detected.
The third study conducted over one year produced cancer related changes in the liver of the mice at a moderate dietary dose of 90 mg/kg. There were no other toxic effects noted for the mice at the highest dose tested (540 mg/kg) (2).
Based on the conflicting evidence presented by the three studies outlined above, no conclusion can be drawn about the overall carcinogenicity of triadimefon.
Organ Toxicity
The compound is non-irritating to the skin and the eyes. Moderate doses (up to 90 mg/kg) of Bayleton have induced a number of different changes in the liver, decreased kidney weights, and altered urinary bladder structure (2).
Fate in Humans and Animals
After oral administration of a single dose of Bayleton, most of the compound was eliminated in the urine and feces unchanged within two to three days. Some breakdown of a small amount of the compound occurred in the liver. The compound has a very short residence time in the blood stream. Half of the initial amount of the compound was removed from the blood within two and a half hours (1).
When applied to the skin of rats, forty percent of the applied amount was excreted in urine and feces within eight days. Additional amounts (up to 40%) were recovered from the skin surface and in the cage (2).
ECOLOGICAL EFFECTS
Effects on Birds
Triadimefon ranges from slightly toxic to practically non-toxic to birds. For instance, the compound has an LD50 value of greater than 4,000 mg/kg in mallard ducks indicating that the compound has little lethal effect on the species (1). Japanese quail are less tolerant of the compound (LD50 of 2,000 mg/kg) and canaries are even less tolerant (LD50 > 1,000 mg/kg) (1). Even the most tolerant species exhibited some compound related toxicity such as diarrhea and regurgitation within five minutes of administration of the highest doses (5). At the lowest dose tested (500 mg/kg) no signs of diarrhea were noted.
Effects on Aquatic Organisms
The compound is slightly toxic to fish, indicating that fish are more susceptible to the presence of the compound than are birds. Bluegill sunfish are the most susceptible followed closely by goldfish, with LC50 values of 11 mg/l and 10mg/l, respectively. The compound is only slightly toxic to rainbow trout (LC50 of 14 mg/l) (1). As with some fish species, Bayleton is moderately toxic to the aquatic invertebrate Daphnia magna, the water flea. The LC50 of the compound in this species is 1.6 mg/l.
Effects on Other Organisms (Nontarget species)
The compound is non-toxic to honeybees.
ENVIRONMENTAL FATE
Research regarding the behavior and fate of the compound in the environment is sparse.
Breakdown of Chemical in Soil and Groundwater
In a sandy loam type of soil half of the initial amount of the compound was lost within eighteen days. In loamy soil the half-life was much shorter (about 6 days) which indicates that breakdown of the compound varies with soil type (6).
No information was found about the compound's potential to leach from soil, or about its potential to accumulate in surface water or groundwater.
Breakdown of Chemical in Surface Water
In water with a pH 3.0, 6.0, or 9.0, almost 95% of the compound remained after 28 weeks. The compound is very stable in water (6).
Breakdown in Vegetation
No information was available.
PHYSICAL PROPERTIES AND GUIDELINES
Triadimefon consists of colorless crystals. It can also be dry flowable or wettable powder, or granule or paste.
Exposure Guidelines:
RfD: NA
HA: NA
ADI: 0.03 mg/kg
PEL: NA
Physical Properties:
Common Name: triadimefon
CAS #: 43121-43-3
Chemical Name: 1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butanone
Molecular weight: 291.73 g/mol
Solubility in water: 260 mg/l at 20 degrees C
Solubility in solvent: Moderately soluble in most organic solvents
Melting Point: 82.3 degrees C
Vapor pressure: < 0.1 mPa at 20 degrees C
Partition coefficient (octanol/water) (log): 3.18
Adsorption coefficient: 300
Chemical class/use: systemic fungicide
BASIC MANUFACTURER
Miles, Inc.
Crop Prot. and Animal Health Div.
8400 Hawthorn Road
P.O. Box 4913
Kansas City, MO 64120
Telephone: (816) 242-2000
Emergency: (816) 242-2582
FAX: (816) 242-2592
Review by Basic Manufacturer:
Comments solicited: April, 1993
Comments received: June, 1993
REFERENCES
The Agrochemicals Handbook: Third Edition. (1991). Royal Society of Chemistry, Unwin Brothers Ltd., Surrey, England.
U.S. Environmental Protection Agency. (1993). Office of Pesticides/ HED/SACB. Tox Oneliners. 3/12/93. Triadimefon.
Maddy, K.T., R.G. Wang, C.M. Au and N. Saini. (1983). Monitoring of Occupational Exposures of Mixer/Loaders and Applicators to Bayleton 50% WP in Kern County in 1982. March 18, 1983.
Farm Chemicals Handbook. (1992). Meister Publishing Co. Willoughby, OH.
Felthousen, R.W. (1978). EEB Branch Review. Bayleton. Environmental Safety Section, Environmental and Ecological Effects Branch, United States Environmental Protection Agency. April 13, 1978.
Environmental Fate and Effects Division. U.S. Environmental Protection Agency. (1990). Pesticide Environmental Fate One Line Summary for Triademifon.
