ENVIROfacts
Syngenta Crop Protection
CHLOROTHALONIL
The Active Ingredient in DACONIL®
Chemical Nomenclature:
Chemical Structure:
Chlorothalonil
2,4,5,6-Tetrachloroisophthalonitrile (IUPAC)
CN
Cl
Cl
CAS No.: 1897-45-6
Cl
CN
Use: Non-systemic, broad spectrum fungicide
Cl
Molecular Formula:
C8Cl4N2
Molecular Weight:
265.9
Physical Properties:
State:
Chemical Stability:
Aqueous Photolysis Half-life:
Physicochemical
Properties:
Aqueous Solubility:
Low (0.81mg/L)
Log Kow:
2.88
Vapor Pressure:
5.72x10-7 mm Hg @
25°C
1 – 40 days
Lab Soil Photolysis Half-life:
Stable
Field Soil Half-life:
10 – 60 days
Koc:
850 – 7000
Mobility Classification:
Low to Immobile
Sediment/Water Dissipation
Half-life:
<8 hours
Application Rates (chlorothalonil):
The maximum single application rate for turf uses is
11.3 lb ai/A. Seasonal maximum is 73 lb ai/A on golf
course greens; 52 lb ai/A on golf tees; and 26 lb ai/A
on golf fairways, sod farms, lawns, other turfgrasses
and ornamental turfgrass. The typical single use rate
is 7.3 lb ai/A. The maximum single rate for
ornamentals is 2.1 lb ai/100 gal with a seasonal
maximum of 36.4 lb ai/A. The maximum single rate for
conifers is 4.125 lb ai/A with a seasonal maximum of
16.5 lb ai/A.
65 days
Aqueous Hydrolysis Half-life:
16-38 days at pH 9
Stable at pH 5 and 7
Volatility:
Non-volatile
Ecotoxicological Profile:
Birds
Environmental Fate
Profile:
Lab Soil Metabolism Halflife:
white, odorless crystalline
powder
Non-toxic
Oral LD50 > 4640 mg/kg
Dietary LC50 > 10,000 ppm
Bees and other non-target
arthropods:
Non-toxic to bees
LD50 > 133 µg ai/bee
Harmless to non-target
arthropods
Earthworms:
Non-toxic
LC50 >404 mg/kg soil
Fish:
Acute LC50 = 10-200 µg/L
Aquatic Invertebrate
(Daphnia):
Acute LC50 = 24->1600
µg/L
Aquatic Plants/Algae:
EC50 = 5.1-210 µg/L
Margin of Safety (Environmental Risk):
Chlorothalonil is of low toxicity to non-target terrestrial
organisms and consequently does not present a risk to these
organisms. Although chlorothalonil is highly toxic to some
aquatic organisms, it does not result in adverse effects in
actual field use. This is due to the rapid rate of dissipation of
chlorothalonil in aquatic environments.
ENVIRONMENTAL OVERVIEW
The safety of a chemical in the environment and potential risk to non-target plants and
animals is a function of its toxicity (hazard) and exposure. Low or no exposure of nontarget organisms limits the potential for any opportunity for toxicological effects in the
environment. The level and duration of exposure is determined by the application rates,
frequency of applications, and the fate and transport of the chemical in the environment.
Chlorothalonil is of low toxicity and consequently low risk to non-target terrestrial
organisms, including birds and mammals, bees and other non-target arthropods,
earthworms, soil microorganisms and plants.
In the terrestrial environment,
chlorothalonil is rapidly degraded by microorganisms. The principal soil degradate is
SDS-3701, which has also been shown to be of low risk to soil organisms and birds and
mammals. Chlorothalonil is not mobile in soil and does not leach to groundwater. The
degradate SDS-3701 is more mobile than the parent, but the potential for leaching to
groundwater is low.
Laboratory studies show that chlorothalonil is highly toxic to aquatic organisms, but its
degradates are significantly less toxic. Any chlorothalonil which might enter aquatic
environments due to spray drift or run-off is rapidly dissipated by degradation,
minimizing exposure and reducing the risk. Studies have shown that the risk of any
effects in aquatic environments is low and there is no potential for any long-term effects.
COMMON QUESTIONS AND ANSWERS
CHARACTERISTICS AND USE PATTERN
What is the mode of action of chlorothalonil against fungi?
Chlorothalonil acts by protecting plants against fungal infection. For best results, the fungicide
must be present on the plant prior to the onset of infection. Infection is prevented due to
interactions between chlorothalonil and fungal cells, which ultimately result in a loss of fungal
cell viability. Studies have indicated that chlorothalonil ties up free glutathione and thus
prevents the activation (reduction) of glyceraldehyde-3-phosphate dehydrogenase and other
similar enzymes. This prevents the fungal cells from obtaining necessary energy to infect
plants. In effect, this stops spore germination and zoospore motility.
What are the characteristics of chlorothalonil?
Chlorothalonil is widely used on many different crops and is typically applied several times a
season with short intervals between applications. Chlorothalonil was first registered in the
United States in 1966 for use on turfgrass. There are approximately 100 chlorothalonil products
and 100 Special Local Need registrations. The use of chlorothalonil represents about 15% of all
U.S. fungicide use by weight. It is a polychlorinated aromatic fungicide, but it does not have a
high degree of persistence like many chlorinated organics due to the two nitrile groups that
activate the molecule. Several of chlorothalonil’s primary metabolites are also polychlorinated
and can be more persistent than the parent compound. SDS-3701 is the most prevalent
degradate and typically reaches amounts equivalent to 10-40% of the total applied parent
compound.
What are the maximum label rates for chlorothalonil?
The maximum single application rate for turf uses is 11.3 lb ai/A with a seasonal maximum of 73
lb ai/A on golf course greens; 52 lb ai/A on golf tees; and 26 lb ai/A on golf fairways, sod farms,
lawns, other turfgrasses and ornamental turfgrass (see diagram below). The typical single use
rate is 7.3 lb ai/A. The maximum single rate for ornamentals is 2.1 lb ai/100 gal with a seasonal
maximum of 36.4 lb ai/A. The maximum single rate for conifers is 4.125 lb ai/A with a seasonal
maximum of 16.5 lb ai/A.
DIAGRAM SHOWING USE RATES FOR GOLF COURSE TEES, GREENS AND FAIRWAYS
Single Max 11.3 lb ai/A
Min Interval 7 d at < 7.3 lb ai/A
Rough*
Min Interval 14 d at > 7.3 lb ai/A
Seasonal max = 26 lb ai/A
*Typically, the seasonal maximum
rate would be 0 lbs ai/A on roughs
No more than 1 app > 7.3 lb ai/A
Tees
.
Greens
Seasonal max = 52 lb ai/A
Seasonal max = 73 lb ai/A
No more than 2 apps > 7.3 lb ai/A
No more than 2 apps > 7.3 lb ai/A
Fairways
Seasonal max = 26 lb ai/A
No more than 1 app > 7.3 lb ai/A
What is the Re-Entry Interval (REI) after using chlorothalonil?
The Re-Entry Interval is 12 hours with 2 provisions: 1) Eyeflush equipment must be available for
6.5 days after application, and 2) Workers must be specifically informed of the eye irritation
hazard, and that eyeflush equipment is available, and how to use the eyeflush equipment.
What diseases are prevented or controlled by chlorothalonil?
Chlorothalonil is used for many fungal diseases on various different crops. Diseases that
chlorothalonil prevents or controls are varieties of molds, blights, mildews, spots, rots, rusts,
blotches, stains, needlecasts, and cankers. Among the most common diseases are Downy
Mildew, Anthracnose, Botrytis Blight/Rot, and Cercospora Leaf Spot/Blight. Ensuring that the
product has adequate time to dry on the foliage after application and prior to rainfall or irrigation
will reduce wash-off and assure efficacy.
How soluble is chlorothalonil in water?
The solubility of chlorothalonil in water is low. Chlorothalonil has low potential for movement in
the environment. This lack of movement is partly due to adsorption by soil particles. If
chlorothalonil is washed into streams or ponds by heavy rainfall after application, it is adsorbed
to soil and is degraded rapidly in the surface water body. When used according to label
directions, chlorothalonil does not present a risk to aquatic organisms.
How volatile is chlorothalonil in the environment?
Chlorothalonil is 4300 times less volatile than glycerin, which is considered to have low volatility.
During applications some extremely low levels of chlorothalonil may enter the atmosphere via
spray drift. Chlorothalonil has been detected in air at very low levels and also in remote
locations from areas of use. This long range transport of chlorothalonil in air is due to the limited
degradation of chlorothalonil in air. The levels found are extremely low and when deposited from
the atmosphere back into the environment the chlorothalonil is rapidly degraded.
ENVIRONMENTAL FATE AND EXPOSURE
What is the half-life of chlorothalonil in water and in the environment?
Chlorothalonil has a short half-life in the environment. Studies have shown that under "realworld" environmental conditions, degradation of chlorothalonil in surface water/sediment, such
as in streams and ponds, is very rapid with a half-life typically less than 8 hours. Chlorothalonil
is bound by organic matter and readily metabolized in soils with short half-lives that depend on
levels of soil microbial activity, moisture, and temperature.
What happens to chlorothalonil when it degrades in soil and sediment?
Chlorothalonil is readily metabolized by aerobic and anaerobic microbial activity in agronomic
soils and aquatic sediments. Some of its degradates are more mobile than chlorothalonil itself
in soil. The principal soil degradates of chlorothalonil are the 4-hydroxy metabolite (SDS-3701)
and the sulphonic acid metabolite (R417888). Multiple pathways exist for the dissipation of
chlorothalonil in the aquatic environment including adsorption to sediment and suspended
matter. Simple hydrolysis and photolysis are not major degradative pathways. Also,
mineralization and evolution of volatiles are not significant.
How do different soil types affect the degradation of chlorothalonil?
Chlorothalonil adsorbs more readily in soils containing high organic matter. As such,
chlorothalonil is highly immobile and resistant to leaching in soils with significant amounts of
organic matter. Microbial degradation is generally higher in silt soils versus sand soils as silt
soils generally have an environment more favorable for microbial activity. Also, chlorothalonil
hydrolyzes slowly in basic conditions but does not hydrolyze in neutral or acid conditions.
If chlorothalonil is not mobile in the soil, why does the label state that chlorothalonil may leach into
groundwater?
These groundwater label statements are generic statements based on the U.S. EPA labeling
requirements for “Environmental Hazards.” They are now required for all products where
degradates are water-soluble with half-lives exceeding a few days.
Why does the label state that spray drift and runoff are concerns when using chlorothalonil? Can
chlorothalonil move off target to non-target water bodies via spray drift or runoff after application?
These statements are based on U.S. EPA labeling requirements for “Environmental Hazards”
and are triggered by laboratory toxicity tests. The statements do not indicate environmental risk
from actual use of chlorothalonil. As with any agricultural pesticide, off-target movement is
possible following use of chlorothalonil, and best management practices should be used to
minimize spray drift and runoff.
The label indicates that untreated buffer zones are required between the treated area and non-target
estuarine/marine environments. How are estuarine/marine environments differentiated from other
bodies of water?
Estuarine/marine environments include brackish water, saltwater, or any tidal areas. Untreated
buffer zones are required between these areas and the treated field where chlorothalonil is
being applied. The untreated buffers must be 25 feet for ground applications and 150 feet for
aerial and air-blast applications.
Is there potential for chlorothalonil, or its degradates, to contaminate groundwater?
Chlorothalonil has been detected in groundwater; however, these detections may have been
due to faulty well construction or contamination. Current studies indicate that parent
chlorothalonil has very limited potential to reach groundwater, even under hydrologically
vulnerable conditions. Chlorothalonil degradates have been found in groundwater, most notably
the degradate SDS-46851. This degradate is not biologically active and therefore presents no
risk. In recent studies the other major soil metabolite, the sulfonic acid metabolite (R417888),
has been shown to be mobile in soil. This degradate is also not biologically active and therefore
presents no risk.
TOXICITY AND RISK TO NON-TARGET ORGANISMS
What is the toxicity and risk to aquatic animals?
Chlorothalonil is considered to be “highly toxic” to “very highly toxic” to fish and aquatic
invertebrates. However any chlorothalonil which might enter aquatic environments due to spray
drift or run-off is rapidly dissipated by degradation, minimizing exposure and reducing the risk.
Chlorothalonil dissipates with a half-life in natural aquatic systems typically less than 8 hours.
There is no long-term exposure. Studies in both the laboratory and the field have shown that the
risk of any effects in aquatic environments is low and there is no potential for any long-term
effects.
How do toxic effects on fish measured in the laboratory relate to actual effects in the environment?
They do not relate directly. Aquatic toxicity studies are conducted in the laboratory in clean
water where there is no sediment or plant material present to mitigate exposure. In laboratory
studies, particularly with fish, concentrations may be maintained throughout exposure whereas
in natural aquatic environments, chlorothalonil rapidly dissipates and presents a low risk to
aquatic organisms.
What is the effect of chlorothalonil on non-target aquatic plants?
The toxicity and risk of chlorothalonil to aquatic plants, as determined by studies with duckweed
(Lemna sp.), is low. Chlorothalonil may be toxic to some green algae. However, there is no risk
of significant effects due to the range of sensitivities of different algal species, the rapid
dissipation of chlorothalonil in water bodies, and recovery rates of algal populations. This has
been confirmed in field studies.
What is the toxicity and risk of chlorothalonil to birds and wild mammals?
Results of several studies on mallards and bobwhite quail indicate that chlorothalonil is nontoxic to birds. Chlorothalonil is non-toxic to mammals and presents low risk to wild mammals.
What is the toxicity of chlorothalonil to honey bees and other non-target arthropods?
Chlorothalonil is non-toxic to honey bees and other non-target arthropods.
What is the effect of chlorothalonil on non-target terrestrial plants?
Chlorothalonil does not significantly affect non-target terrestrial plants at maximum labeled
application rates as indicated in plant studies that assessed seed germination, seedling
emergence, vegetative vigor, and phytotoxicity.
What is the toxicity of the degradate SDS-3701 to aquatic organisms?
SDS-3701 is “slightly toxic” to aquatic organisms and is significantly less toxic than the parent
compound. The risk of effects from SDS-3701 residues in aquatic systems is negligible. The
effect of SDS-3701 on non-target aquatic plants is also negligible due to its low toxicity.
What is the toxicity of the degradate SDS-3701 to birds and wild mammals? Will SDS-3701 affect birds
and mammals in the wild?
Using studies with mallards and bobwhite quail, it has been determined that SDS-3701 is
“slightly toxic” to “moderately toxic” to birds and can also affect avian reproduction, albeit at
concentrations well above environmental exposures. SDS-3701 is also moderately toxic to small
mammals in laboratory studies. Residues of SDS-3701 are low in the environment, resulting in
minimal exposure. Given this, there is no risk to birds and wild mammals from exposure to SDS3701.
DIETARY RISK
Were chlorothalonil rates and number of applications limited due to dietary risk?
No. Dietary risk was recently assessed as part of the USEPA re-registration process and the
Food Quality Protection Act, and did not result in a need to limit rates and applications. Rates
and number of applications were limited due to ecological risk at higher rates.
PROCEDURES FOR SPILL
What are the procedures to take if there is a chlorothalonil spill?
Contain the spill by diking and by adding adsorbent materials. Every effort should be made to
keep the spill from reaching lakes, streams, ponds, or open sewers. Remove as much of the
spilled chlorothalonil as possible (shovel and sweep up), and remove soil containing
chlorothalonil. Contaminated soil and materials should be placed in closed containers, which
should be labeled and stored in a safe place until proper disposition can be made. Do not
contaminate water while cleaning equipment or disposing of wastes. Persons performing this
work should wear adequate personal protective equipment and clothing, as indicated on the
product label. Neutralizing chemicals are not required. Call 1-800-888-8372 to report the spill
and for further assistance.
Important: Always read and follow label instructions before buying or using these products
Syngenta Crop Protection, Inc. warrants that its products conform to the chemical description set forth on the
products’ labels. NO OTHER WARRANTIES, WHETHER EXPRESS OR IMPLIED, INCLUDING WARRANTIES OF
MERCHANTABILITY AND OF FITNESS FOR A PARTICULAR PURPOSE, SHALL APPLY TO SYNGENTA’S
PRODUCTS. Syngenta Crop Protection, Inc. neither assumes nor authorizes any representative or other person to
assume for it any obligation or liability other than such as is expressly set forth herein. UNDER NO
CIRCUMSTANCES SHALL SYNGENTA CROP PROTECTION, INC. BE LIABLE FOR INCIDENTAL OR
CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR HANDLING OF ITS PRODUCTS. No statements
or recommendations contained herein are to be construed as inducements to infringe any relevant patent now or
hereafter in existence.
DACONIL® is a Registered Trademark of the Syngenta Group
© 2003 Syngenta Group