Chlorothalonil

data) 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. ==Mechanism of action==

Chlorothalonil reacts with glutathione giving an glutathione adduct with elimination of HCl. Its mechanism of action is similar to that of trichloromethyl sulfenyl fungicides such as captan and folpet. ==Toxicity==

Acute 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 0.094 mg/L in rats.) For skin contact and ingestion, chlorothalonil is rated toxicity category IV, "practically nontoxic", meaning the oral and dermal 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 day. Contaminants 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-Tetrachlorodibenzodioxin being one of the most potent carcinogens known is also a known contaminant". ==Environmental contamination==

Chlorothalonil has been detected in ambient air Prince Edward Island, as well as in groundwater in Long Island, New York The main breakdown product of chlorothalonil is SDS-3701 (structure shown below). SDS-3701 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. Agrochemicals are claimed to be the strongest factor in bumblebee population decline. Bans In March 2019, as a result of the previously mentioned research, the European Union banned the use of chlorothalonil ==Production==

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 TCDD and hexachlorobenzene, both are persistent organic pollutants banned under the Stockholm Convention. ==References==