Chlorothalonil, also known as tetrachloroisophthalonitrile, is a broad spectrum, non-systemic fungicide. 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 is available, it was the third most used fungicide in the US, behind only sulfur and copper, with some 12 million lbs used in agricultural alone that year. Including non-agricultural uses, the EPA estimates that on average almost 15 million lbs were used in annually from 1990-1996.
In the US, chlorothalonil is used predominantly on peanuts
, and tomatoes
. It is also used on golf courses and lawns and as an additive in some paints.
According to the United States Environmental Protection Agency
, chlorothalonil is a Category I "severe" eye irritant. It is not considered to be acutely toxic by ingestion (its oral LD50
is greater than 10,000 mg/kg), but is toxic when inhaled. In animal tests, long term chlorothalonil exposure resulted in kidney
damage. Chlorothalonil is a class B2 "probable carcinogen
", based on observations of cancers
of the kidneys and forestomach
in laborotory animals fed diets containing chlorothalonil.
Chlorothalonil is highly toxic to fish and aquatic Invertebrates, but not toxic to birds.
Chlorothalonil has been detected in ambient air in Minnesota
and Prince Edward Island
. In both cases, the contamination is presumed to have come from potato farms.
The main breakdown product of chlorothalonil is SDS-3701 (4-hydroxy-2,5,6-trichloroisophthalonitrile). It has been shown to be 30 times more acutley toxic than chlorothalonil and more persistent in the environment. Laboratory experiments have shown that it can thin the eggshells of birds, but there is no evidence that this is happening in the environment.
Chlorothalonil can by produced by the direct chlorination of isophthalonitrile or by treating tetrachloroisophthaloyl amide with phosphoryl chloride
. It breaks down under basic conditions but is stable in neutral and acidic media. Technical chlorothalonil contains traces of dioxins
, a persistent organic pollutant
banned under the Stockholm Convention