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Syngenta Crop Protection
CHLOROTHALONIL
The Active Ingredient in BRAVO®
Chemical Structure:
Chlorothalonil
Chemical Nomenclature:
2,4,5,6-Tetrachloroisophthalonitrile (IUPAC)
CN
Cl
Cl
Cl
CN
CAS No.: 1897-45-6
Use: Non-systemic, broad spectrum fungicide
Cl
Molecular Formula:
C8Cl4N2
Molecular Weight:
265.9
Physicochemical Properties:
Aqueous Solubility:
Low (0.81mg/L)
Chemical Stability:
Aqueous Photolysis Half-life:
Log Kow:
2.88
Aqueous Hydrolysis Half-life:
16-38 days at pH 9
Stable at pH 5 and 7
Volatility:
Ecotoxicological Profile:
Birds
Non-volatile
Vapor Pressure:
Physical Properties:
State:
-7
white, odorless crystalline
powder
65 days
5.72x10 mm Hg @ 25°C
Environmental Fate Profile:
Lab Soil Metabolism Half-life:
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 application rate on crops is 5 lb ai/A and the
typical rate is 2.23 lb ai/A. The maximum application rate per
season for crops is 18 lb ai/A.
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:
Aquatic Invertebrate (Daphnia):
Acute LC50 = 10 -200 µg/L
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 any potential risk to non-target animals
and plants is a function of its toxicity (hazard) and exposure. Low or no exposure of
non-target 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 principle 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 turf grass. 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 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.
What are the maximum label rates for chlorothalonil?
The maximum use rate varies among the crops. Most crops have a maximum rate between
1.5-2.25 lb ai/A. Two crops have use rates as high as 4.5-5.0 lb ai/A. The maximum seasonal
load is generally 15-18 lb ai/A. Some uses allow up to 24 lb ai/A/season.
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 principle 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.
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 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.
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.
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 the
degradates are water-soluble with half-lives exceeding a few days.
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 is 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 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 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 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.
BRAVO® is a Registered Trademark of the Syngenta Group
© 2003 Syngenta Group