Chlorothalonil
Encyclopedia
Chlorothalonil is a polychlorinated aromatic mainly used as a broad spectrum, non-systemic 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 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.
(about 34% of US usage), potatoes (about 12%), and tomatoes (about 7%), though 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.
molecules to alternate forms which cannot participate in essential enzymatic
reactions, ultimately leading to cell death, similar to the mechanism of trichloromethyl sulfenyl.
, 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 non-toxic," meaning the oral and dermal is greater than 10,000 mg/kg.
damage and tumors in animal tests.
", based on observations of cancers and tumors of the kidneys and forestomach in laboratory animals fed diets containing chlorothalonil. ticides.
Chlorothalonil has been suggested as a partial cause of Colony Collapse Disorder
, among many other factors.
At a concentration of 164µg/L, chlorothalonil was found to kill test a species of frog within a 24h exposure.
, which is itself 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."
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.
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.
. It breaks down under basic conditions but is stable in neutral and acidic media. Technical chlorothalonil contains traces of dioxins
and hexachlorobenzene
, a persistent organic pollutant
banned under the Stockholm Convention
.
Fungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
, with other uses as a wood protectant, pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
, acaricide, and to control mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
, mildew
Mildew
Mildew refers to certain kinds of molds or fungi.In Old English, it meant honeydew , and later came to mean mildew in the modern sense of mold or fungus....
, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
. 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
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, with some 12 million lbs used in agricultural alone that year. Including non-agricultural uses, the EPA
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
estimates that on average almost 15 million lbs were used in annually from 1990-1996.
Uses
In the US, chlorothalonil is used predominantly on peanutsPeanuts
Peanuts is a syndicated daily and Sunday American comic strip written and illustrated by Charles M. Schulz, which ran from October 2, 1950, to February 13, 2000, continuing in reruns afterward...
(about 34% of US usage), potatoes (about 12%), and tomatoes (about 7%), though 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
Wettable powder
A Wettable Powder is an insecticide or other pesticide formulation consisting of the active ingredient in a finely ground state combined with wetting agents and sometimes bulking agents. Wettable powers are designed to be applied as a dilute suspension through liquid spraying equipment...
, a liquid spray, a fog, and a dip. It may be applied by hand, by ground sprayer, or by aircraft.
Mechanism of action
Chlorothalonil reduces fungal intracellular glutathioneGlutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...
molecules to alternate forms which cannot participate in essential enzymatic
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
reactions, ultimately leading to cell death, similar to the mechanism of trichloromethyl sulfenyl.
Acute
According to the United States Environmental Protection AgencyUnited States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
, chlorothalonil is a Toxicity Category I
Toxicity category rating
Section 156.62 of Title 40 of the Code of Federal Regulations establishes four Toxicity Categories for acute hazards of pesticide products, Category I being the highest toxicity category. Most human hazard, precautionary statements, and human personal protective equipment statements are based upon...
eye irritant, producing severe eye irritation. It is in Toxicity Category II
Toxicity category rating
Section 156.62 of Title 40 of the Code of Federal Regulations establishes four Toxicity Categories for acute hazards of pesticide products, Category I being the highest toxicity category. Most human hazard, precautionary statements, and human personal protective equipment statements are based upon...
, "moderately toxic," if inhaled (inhaled 0.094 mg/L in rats.) For skin contact and ingestion, chlorothalonil is rated Toxicity Category IV
Toxicity category rating
Section 156.62 of Title 40 of the Code of Federal Regulations establishes four Toxicity Categories for acute hazards of pesticide products, Category I being the highest toxicity category. Most human hazard, precautionary statements, and human personal protective equipment statements are based upon...
, "practically non-toxic," meaning the oral and dermal is greater than 10,000 mg/kg.
Chronic
Long term exposure to chlorothalonil resulted in kidneyKidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
damage and tumors in animal tests.
Carcinogenic
Chlorothalonil is a Group B2 "probable human carcinogenCarcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
", based on observations of cancers and tumors of the kidneys and forestomach in laboratory animals fed diets containing chlorothalonil. ticides.
Environmental
Chlorothalonil is highly toxic to fish and aquatic invertebrates, but not toxic to birds.Chlorothalonil has been suggested as a partial cause of Colony Collapse Disorder
Colony Collapse Disorder
Colony collapse disorder is a phenomenon in which worker bees from a beehive or European honey bee colony abruptly disappear. While such disappearances have occurred throughout the history of apiculture, the term colony collapse disorder was first applied to a drastic rise in the number of...
, among many other factors.
At a concentration of 164µg/L, chlorothalonil was found to kill test a species of frog within a 24h exposure.
Contaminants
Common chlorothalonil synthesis procedures frequently result in chlorothalonil contaminated with small amounts of hexachlorobenzeneHexachlorobenzene
Hexachlorobenzene, or perchlorobenzene, is a chlorocarbon with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt...
, which is itself 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."
Environmental contamination
Chlorothalonil has been detected in ambient air in MinnesotaMinnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
and Prince Edward Island
Prince Edward Island
Prince Edward Island is a Canadian province consisting of an island of the same name, as well as other islands. The maritime province is the smallest in the nation in both land area and population...
, as well as in groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
in Long Island, New York and Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
. In the first three 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.
Chemistry
Chlorothalonil can by produced by the direct chlorination of isophthalonitrile or by treating tetrachloroisophthaloyl amide with phosphoryl chloridePhosphoryl chloride
Phosphoryl chloride is a colourless liquid with the formula 3. It hydrolyses in moist air to phosphoric acid to release choking fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide...
. It breaks down under basic conditions but is stable in neutral and acidic media. Technical chlorothalonil contains traces of dioxins
Dioxins and dioxin-like compounds
Dioxins and dioxin-like compounds are by-products of various industrial processes, and are commonly regarded as highly toxic compounds that are environmental pollutants and persistent organic pollutants . They include:...
and hexachlorobenzene
Hexachlorobenzene
Hexachlorobenzene, or perchlorobenzene, is a chlorocarbon with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt...
, a persistent organic pollutant
Persistent organic pollutant
thumb|right|275px|State parties to the Stockholm Convention on Persistent Organic PollutantsPersistent organic pollutants are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes...
banned under the Stockholm Convention
Stockholm Convention
Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed in 2001 and effective from May 2004, that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
.