Chlorothalonil

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. 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. Chlorothalonil reduces deactivates glutathione. Its mechanism of action is similar to that of trichloromethyl sulfenyl fungicides such as captan and folpet. 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. Long-term exposure to chlorothalonil resulted in kidney damage and tumors in animal tests. Chlorothalonil is a Group B2 'probable human carcinogen', based on observations of cancers and tumors of the kidneys and forestomachs in laboratory animals fed diets containing chlorothalonil. Chlorothalonil was found to be an important factor in the decline of the honey bee population, by making the bees more vulnerable to the gut parasite Nosema ceranae.