Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) is an organic compound mainly used as a broad spectrum, nonsystemic fungicide, with other uses as a wood protectant, pesticide, acaricide, and to control mold, mildew, bacteria, algae. Chlorothalonil-containing products are sold under the names Bravo, Echo, and Daconil. It was first registered for use in the US in 1966. In 1997, the most recent year for which data are available, it was the third most used fungicide in the US, behind only sulfur and copper, with 12 million pounds (5.4 million kilograms) used in agriculture that year. Including nonagricultural uses, the United States Environmental Protection Agency (EPA) estimates, on average, almost 15 million lb (6.8 million kg) were used annually from 1990 to 1996.
|Preferred IUPAC name
3D model (JSmol)
|UN number||3276, 2588|
CompTox Dashboard (EPA)
|Molar mass||265.90 g·mol−1|
|Appearance||white crystalline solid|
|Density||1.8 g cm−3, solid|
|Melting point||250 °C (482 °F; 523 K)|
|Boiling point||350 °C (662 °F; 623 K) (760 mmHg)|
|10 mg/100 mL|
|GHS signal word||Danger|
|H317, H318, H330, H335, H351, H400, H410|
|P201, P202, P260, P261, P271, P272, P273, P280, P281, P284, P302+352, P304+340, P305+351+338, P308+313, P310, P312, P320, P321, P333+313, P363, P391, P403+233, P405, P501|
hexachlorobenzene, dichlorobenzene, chlorobenzene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
In the US, chlorothalonil is used predominantly on peanuts (about 34% of usage), potatoes (about 12%), and tomatoes (about 7%), although the EPA recognizes its use on many other crops. It is also used on golf courses and lawns (about 10%) and as a preservative additive in some paints (about 13%), resins, emulsions, and coatings.
Chlorothalonil is commercially available in many different formulations and delivery methods. It is applied as a dust, dry or water-soluble grains, a wettable powder, a liquid spray, a fog, and a dip. It may be applied by hand, by ground sprayer, or by aircraft.
Mechanism of actionEdit
According to the EPS, chlorothalonil is a toxicity category I eye irritant, producing severe eye irritation. It is in toxicity category II, "moderately toxic", if inhaled (inhaled LD50 0.094 mg/l in rats.) For skin contact and ingestion, chlorothalonil is rated toxicity category IV, "practically nontoxic", meaning the oral and dermal LD50 is greater than 10,000 mg/kg.
Chlorothalonil is highly toxic to fish and aquatic invertebrates, but not toxic to birds.
At a concentration of 164 µg/L, chlorothalonil was found to kill a species of frog within a 24-hour exposure.
Common chlorothalonil synthesis procedures frequently result in contamination of it with small amounts of hexachlorobenzene(HCB), which is toxic. US regulations limit HCB in commercial production to 0.05% of chlorothalonil. According to the EPA report, "post-application exposure to HCB from chlorothalonil is not expected to be a concern based on the low level of HCB in chlorothalonil. 2,3,7,8 Tetrachlorodibenzo-Dioxin being one of the most potent carcinogens known is also a known contaminant"
Chlorothalonil has been detected in ambient air in Minnesota and Prince Edward Island, as well as in groundwater in Long Island, New York and Florida. In the first three cases, the contamination is presumed to have come from potato farms. It has also been detected in several fish kills in Prince Edward Island.
The main breakdown product of chlorothalonil is hydroxy-2,5,6-trichloro-1,3-dicyanobenzene (SDS-3701). It has been shown to be 30 times more acutely toxic than chlorothalonil and more persistent in the environment. Laboratory experiments have shown it can thin the eggshells of birds, but no evidence supports this happening in the environment.
In 2019, European Union states voted overall to ban chlorothalonil after a review of the evidence found that "a high risk to amphibians and fish was identified for all representative uses", and that chlorothalonil breakdown products may cause DNA damage. Around the same time, research indicated chlorothalonil and other fungicides to be the strongest factor in bumblebee population decline.
Chlorothalonil can be produced by the direct chlorination of isophthalonitrile or by dehydration of tetrachloroisophthaloyl amide with phosphoryl chloride. It is a white solid. It breaks down under basic conditions, but is stable in neutral and acidic media. Technical grade chlorothalonil contains traces of dioxins and hexachlorobenzene, a persistent organic pollutant banned under the Stockholm Convention.
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- Cox, Caroline (1997), "Fungicide Factsheet: Chlorothalonil", Journal of Pesticide Reform, 17 (4): 14–20, archived from the original on 10 November 2010
- Carrington, Damian (29 March 2019). "EU bans UK's most-used pesticide over health and environment fears". the Guardian. Retrieved 29 March 2019.
- "European Commission votes to ban fungicide Chlorothalonil".
- Franz Müller, Peter Ackermann, Paul Margot. "Fungicides, Agricultural, 2. Individual Fungicides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.o12_o06.CS1 maint: uses authors parameter (link)
- Extension Toxicology Network: Chlorothalonil Pesticide Information Profile
- Chlorothalonil in the Pesticide Properties DataBase (PPDB)