Chlorothalonil

Description

Chlorothalonil is a pesticide fungicide commonly used in the cultivation of ornamental plants and flowers, rice, and onions. In banana plantations it is used in fumigations by airplanes. It can be used as a preservative of paints and of woods. Chlorothalonil can induce contact urticaria, irritant and allergic contact dermatitis, erythema dychromicum perstans or folliculitis mainly in agricultural workers, in those in wood-related professions or in hortieulturists.

Chemical properties

Chlorothalonil is a combustible, white, odorless, crystalline solid

The Uses of Chlorothalonil

Chlorothalonil is a polychlorinated aromatic broad spectrum non-systematic fungicide. Chlorothalonil is used heavily in agriculture field on crops such as peanuts, potatoes and tomatoes. Chlorothaloni l is a probable human carcinogen (Group B2) and is highly toxic to fish and aquatic invertabrates.

The Uses of Chlorothalonil

Chlorothalonil is a non-systemic foliar fungicide with protective activity. It is used to control a broad spectrum of fungal diseases in fruit (pome, stone, citrus, etc.), berries, vegetables, cucurbits, root crops, soyabeans, ornamentals and turf.

What are the applications of Application

Chlorothalonil is a broad spectrum fungicide with carcinogenic and aquatic toxicity properties

Definition

ChEBI: A dinitrile that is benzene-1,3-dicarbonitrile substituted by four chloro groups. A non-systemic fungicide first introduced in the 1960s, it is used to control a range of diseases in a wide variety of crops.

General Description

Colorless crystals or granules or light gray powder. Melting point 250-251°C. No odor when pure; technical grade has a slightly pungent odor. A fungicide formulated as water-dispersible granules, wettable powder, or dust.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Chlorothalonil is stable in neutral or acidic aqueous media. May react violently with strong oxidizing acids [Farm Chemicals Handbook]. Incompatible with other oxidizing agents such as peroxides and epoxides. Breaks down slowly in basic aqueous media (half-life 38.1 days at pH 9. [Farm Chemicals Handbook].

Health Hazard

Chlorothalonil is an irritant to the skin and eyes and has been reported to produce allergic contact dermatitis in exposed workers.

Fire Hazard

Literature sources indicate that Chlorothalonil is nonflammable.

Flammability and Explosibility

Not classified

Agricultural Uses

Fungicide: Chlorothalonil is a broad-spectrum fungicide. It is used on vegetables, peanuts, potatoes, small fruits, trees, turf, roses, ornamentals, and other crops. In California, the top crops are tomatoes, onions, celery, and landscaping. It targets fungal blights, needlecasts, and cankers on conifer trees. This is the second most used fungicide in the U.S. It can be found in formulations with many other pesticides

Trade name

ATLAS CROPGARD®; BANOL C®; BB CHLOROTHALONIL®; BOMmHgDIER®; BRAVO®; BRAVO® 6 F; BRAVO® 500; BRAVO® 6 F; BRAVO ULTREX®; BRAVO-W-75®; CHILTERN OLE®; CONTACT® 75; DAC® 2787; DACONIL®; DACONIL® 2787 FUNGICIDE; DACONIL® 2787 W; DACONIL® F; DACONIL® M; DACONIL® TURF; DACOSOIL®; DIVA FUNGICIDE®[C]; ECHO®; EXOTHERM®; EXOTHERM TERMIL®; FORTURF®; FUNGINIL®; IMPACT EXCEL®; JUPITAL®; NUOCIDE®; OLE®; PILLARICH®; POWER CHLOROTHALONIL® 50; REPULSE®; RIDOMIL GOLD/BRAVO®; SICLOR®; SIPCAM® UK ROVER 5000; SWEEP®; TER-MIL®; TPN®; TPN (PESTICIDE)®; TRIPART FABER®; TRIPART ULTRAFABER®; TUFFCIDE®

Contact allergens

Chlorothalonil is a fungicide widely used in the cultivation of ornamental plants and flowers, rice, and onions. In banana plantations it is used in fumigations by airplanes. It can be used as a preservative of paints and woods. It can induce contact urticaria, irritant and allergic contact dermatitis, erythema dyschromicum perstans, or folliculitis mainly in agricultural workers, wood-related professions, or in horticulturists.

Pharmacology

Mechanism of action of this fungicide may be attributed to inhibition of physiological activities of fungal cell constituents by binding reaction. The reaction was observed in buffer solution to substitute hydroxyethylthio radical(s) of 2-mercaptoethanol for chlorine radical(s) on the benzene ring of the fungicide molecule preferably at 4-position (i.e., also 6-) followed by other positions (5). Similar reactions in fungal cells were observed between the fungicide and glutathione and high molecular weight cell constituents having a sulfhydryl group (5,6). The fungicide inhibits activities of thiol-dependent enzymes such as alcohol dehydrogenase, gyceraldehyde-3-phosphate dehydrogenase, and malate dehydrogenase (5,6). Preliminary addition of glutathione or dithiothreitol protects the thiol enzymes from inhibition but later addition does not reverse the enzyme inhibition. Chymotrypsin, a non-thiol enzyme, was not inhibited by this fungicide. Binding of the fungicide to the sulfhydryl group of cell constituents appears to be the primary mode of its action.

Safety Profile

Suspected carcinogen with experimental carcinogenic data. Moderately toxic by skin contact and intraperitoneal routes. Mildly toxic by ingestion. Mutation data reported. When heated to decomposition it emits very toxic fumes of Cl-, NOx, and CN-. See also NITRILES.

Potential Exposure

Chlorothalonil is a broad spectrum fungicide; used as fungicide in coatings; caulk, wood preservative, and antifouling systems. Therefore, people involved in its manufacture, formulation, and application can be exposed.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least2030 min, occasionally lifting upper and lower lids. Seekmedical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit

Carcinogenicity

Chlorothalonil was not mutagenic in a variety of assays, nor did it bind to DNA.3 The compound does not appear to have genotoxic potential and probably exerts its carcinogenic action in rodents via a nongenotoxic mechanism. 3 Rodent models may be a poor predictor of carcinogensis in humans because of species differences in metabolic pathways leading to carcinogenesis in the kidney and the lack of a comparable organ (forestomach) in humans.
The IARC has determined that there is sufficient evidence for carcinogenicity of chlorothalonil in experimental animals and inadequate evidence in humans.

Environmental Fate

Biological. From the first-order biotic and abiotic rate constants of chlorothalonil in estuarine water and sediment/water systems, the estimated biodegradation half-lives were 8.1–10 and 1.8–5 days, respectively (Walker et al., 1988).
Soil. Metabolites identified in soil were 1,3-dicyano-4-hydroxy-2,5,6-trichlorobenzene, 1,3-dicarbamoyl-2,4,5,6-tetrachlorobenzene and 1-carbamoyl-3-cyano-4-hydroxy-2,5,6- trichlorobenzene (Rouchaud et al., 1988). The half-life was reported as 4.
Groundwater. According to the U.S. EPA (1986) chlorothalonil has a high potential to leach to groundwater
Plant. Degrades in plants to 4-hydroxy-2,5,6-trichloroisophthalonitrile (Hartley and Kidd, 1987), 1,3-dicyano-4-hydroxy-2,5,6-trichlorobenzene and 1,3-dicarbamoyl-2,4,5,6- tetrachlorobenzene (Rouchaud et al., 1988). No evidence of degradation products were reported in apple foliage 15 days after application. The half-life of chlorothalonil was 4.1 days (Gilbert, 1976)

Metabolic pathway

By in vitro incubation of 14C-chlorothalonil (CTL) with rat stomach, duodenum, and cecum contents, with dog stomach, duodenum, and colon contents, and with human feces and stomach contents, transformation of CTL mostly occurs in rat cecum contents, dog colon contents, and human feces, in which unchanged CTL accounts for 46.7, 29.7, and 22.6% of applied radioactivity, respectively. In those incubations, the identified metabolites are 2,5,6-trichloro-4- methylthioisophthalonitrile, 2,5,6-trichloro-4- thioisophthalonitrile, 3-thia-1-cyano-2,5,6- trichloroisoindolinone, 2,5,6-trichloro-4- hydroxyisophthalonitrile, and 2,5,6- trichloroisophthalonitrile. In rats, CTL is transformed to 4,6-bis(N-acetylcystein-S-yl)-2,5- dichloroisophthalonitrile.
The photolysis of CTL solutions in alcohols (ethanol and methanol separately) with exposure to UV irradiation yields 4,5,7-trichloro-6-cyano-3- methylbenzo-g -lactone and dichlorobenzo-bis-g -lactone derivatives as major degradation products in ethanol. In methanol, 4,5,7-trichloro-6-cyanobenzo-g -lactone is the only photoproduct detected.

Metabolism

Degradation pathways of chlorothalonil in upland and paddy soils (7) and by soil bacteria (8) were studied, and most initial products were identified to be the results of chlorine substitution reactions, by hydrogen (i.e., dechlorination), by hydroxyl, and by methylthio groups. These reactions took place first at the 4-position of the ring followed by reactions at other positions as in the reaction with thiol compounds. Paddy soil degraded the fungicide faster than did upland soil. Chlorine substitution reaction at 4-position of the fungicide molecule was also reported in benzene solution under sunlight, and the phenyl-substituted product was identified (9). Similar photolysis was observed in other aromatic hydrocarbon solutions but not in acetone, hexane, and ether solutions.

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working with chlorothalonil you should be trained on its proper handling andstorage. Store in tightly closed containers in a cool, wellventilated area. Metal containers involving the transfer ofthis chemical should be grounded and bonded. Drums mustbe equipped with self-closing valves, pressure vacuumbungs, and flame arresters. Use only nonsparking tools andequipment, especially when opening and closing containersof this chemical. Sources of ignition, such as smoking andopen flames, are prohibited where this chemical is used,handled, or stored in a manner that could create a potentialfire or explosion hazard. A regulated, marked area shouldbe established where this chemical is handled, used, orstored in compliance with OSHA Standard 1910.1045

Shipping

UN3276 Nitriles, liquid, toxic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required, Potential Inhalation Hazard (Special Provision 5). UN2588 Pesticides, solid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required

Degradation

Chlorothalonil is stable to aqueous hydrolysis at pH values above 7. It is hydrolysed slowly at pH 9 via dechlorination to yield 4-hydroxy-2,5,6- trichloroisothalonitrile (2) and oxidation/hydration of one of the nitrile groups to yield 3-cyano-2,4,5,6-tetrachlorobenzamide (3) (Szalkowski and Stallard, 1977).

Toxicity evaluation

Chlorothalonil’s production and use as a broad-spectrum, nonsystemic, protectant pesticide results in its direct release to the environment. Its uses as a wood protectant, antimold and antimildew agent, bactericide, microbiocide, algaecide, insecticide, and acaricide are additional routes of release. If released to air, chlorothalonil will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase chlorothalonil will be degraded slowly in the atmosphere by reaction with photochemically produced hydroxyl radicals (reaction half-life ～7 years). Direct photolysis may also occur. Chlorothalonil is removed from the atmosphere by wet and dry deposition. If released to soil, chlorothalonil is expected to have lowmobility or be immobile, based on Koc values in the range of 900–7000 measured in four soils. Volatilization from moist or dry soil surfaces is not expected to be important based on a Henry’s Law constant of 2.5×10^-7 atm-cummol^-1. Aerobic biodegradation half-lives of chlorothalonil in four different soils ranged from 10 to 40 days. If released into water, chlorothalonil is expected to adsorb to suspended solids and sediment in the water column.

Incompatibilities

Contact with strong oxidizers may cause a fire and explosion hazard. Thermal decomposition may include fumes of hydrogen cyanide. Nitriles may polymerize in the presence of metals and some metal compounds. They are incompatible with acids; mixing nitriles with strong oxidizing acids can lead to extremely violent reactions. Nitriles are generally incompatible with other oxidizing agents such as peroxides and epoxides. The combination of bases and nitriles can produce hydrogen cyanide. Nitriles are hydrolyzed in both aqueous acid and base to give carboxylic acids (or salts of carboxylic acids). These reactions generate heat. Peroxides convert nitriles to amides. Nitriles can react vigorously with reducing agents. Acetonitrile and propionitrile are soluble in water, but nitriles higher than propionitrile have low aqueous solubility. They are also insoluble in aqueous acids.

Waste Disposal

Incineration in a unit operating @ 850C equipped with off-gas scrubbing equipment.