Chlorothalonil

Chlorothalonil
Names
Preferred IUPAC name
2,4,5,6-Tetrachlorobenzene-1,3-dicarbonitrile
Other names
2,4,5,6-Tetrachloroisophthalonitrile
Bravo
Daconil
Tetrachloroisophthalonitrile
Celeste
Bronco
Agronil
Aminil
Identifiers
1897-45-6 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:3639 N
ChEMBL ChEMBL468167 N
ChemSpider 13861400 YesY
ECHA InfoCard 100.015.990
KEGG C11037 N
RTECS number NT2600000
UNII J718M71A7A N
Properties
C8Cl4N2
Molar mass 265.91 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)
0.06 g/100 ml
log P 2.88–3.86
Related compounds
benzonitrile;
hexachlorobenzene, dichlorobenzene, chlorobenzene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

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.[1] 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 some 12 million pounds used in agriculture alone that year.[2] Including nonagricultural uses, the EPA estimates, on average, almost 15 million pounds were used annually from 1990-1996.[1]

Uses

In the US, chlorothalonil is used predominantly on peanuts (about 34% of usage), potatoes (about 12%), and tomatoes (about 7%), though the EPA recognizes its use on many other crops.[1] 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.[1]

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.[1]

Mechanism of action

Chlorothalonil reduces fungal intracellular glutathione molecules to alternate forms which cannot participate in essential enzymatic reactions, ultimately leading to cell death, similar to the mechanism of trichloromethyl sulfenyl.[3]

Toxicity

Acute

According to the United States Environmental Protection Agency, 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.[1]

Chronic

Long-term exposure to chlorothalonil resulted in kidney damage and tumors in animal tests.[1]

Carcinogenic

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.[1]

Environmental

Chlorothalonil was found to be an important actor in the decline of the honey bee population, by making the bees more vulnerable to the gut parasite Nosema ceranae.[4]

Chlorothalonil is highly toxic to fish and aquatic invertebrates, but not toxic to birds.[5]

At a concentration of 164 µg/l, chlorothalonil was found to kill a species of frog within a 24-hour exposure.[6]

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 Tetrachlorodibenzo-Dioxin being one of the most potent carcinogens known is also a known contaminant"[1]

Environmental contamination

Chlorothalonil has been detected in ambient air in Minnesota[7] and Prince Edward Island,[8] as well as in groundwater in Long Island, New York[1] and Florida.[1] In the first three cases, the contamination is presumed to have come from potato farms.

The main breakdown product of chlorothalonil is 4-hydroxy-2,5,6-trichloroisophthalonitrile (SDS-3701). It has been shown to be 30 times more acutely toxic than chlorothalonil and more persistent in the environment.[9] Laboratory experiments have shown it can thin the eggshells of birds, but no evidence supports this happening in the environment.[1]

Production

Chlorothalonil can be produced by the direct chlorination of isophthalonitrile or by dehydration of tetrachloroisophthaloyl amide with phosphoryl chloride.[10] It is a white solid. It breaks down under basic conditions, but is stable in neutral and acidic media.[5] Technical grade chlorothalonil contains traces of dioxins and hexachlorobenzene,[1] a persistent organic pollutant banned under the Stockholm Convention.

Chlorothalonil use in the US in pounds per square mile in 2002, Source: USGS

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 Reregistration Eligibility Decision for chlorothalonil, US EPA, 1999.
  2. ↑ PESTICIDE USE IN U.S. CROP PRODUCTION: 1997 National Center for Food and Agricultural Policy, 1997.
  3. ↑ Tillman, Ronald; Siegel, Malcom; Long, John (June 1973), "Mechanism of action and fate of the fungicide chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) in biological systems : I. Reactions with cells and subcellular components of Saccharomyces pastorianus", Pesticide Biochemistry and Physiology, 3 (2): 160–167, doi:10.1016/0048-3575(73)90100-4
  4. ↑ Jeffery S. Pettis,Elinor M. Lichtenberg,Michael Andree,Jennie Stitzinger,Robyn Rose, Dennis vanEngelsdorp "Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae" PLOS ONE, 24 July 2013, Online: 9 April 2014.
  5. 1 2 Environmental Health Criteria 183, World Health Organization, 1996.
  6. ↑ Taegan McMahon, Neal Halstead, Steve Johnson, Thomas R. Raffel, John M. Romansic, Patrick W. Crumrine, Raoul K. Boughton, Lynn B. Martin, Jason R. Rohr "The Fungicide Chlorothalonil is Nonlinearly Associated with Corticosterone Levels, Immunity, and Mortality in Amphibians" Environ Health Perspectives, 2011, Online: 4 April. doi:10.1289/ehp.1002956
  7. ↑ Pesticides and Air Pollution in Minnesota: The Frequency of Detection of Chlorothalonil, a Fungicide Used on Potatoes. Pesticide Action Network North America, Oct 2007.
  8. ↑ White LM, Ernst WR, Julien G, Garron C, Leger M (2006). "Ambient air concentrations of pesticides used in potato cultivation in Prince Edward Island, Canada". Pest Manag. Sci. 62 (2): 126–36. doi:10.1002/ps.1130. PMID 16358323.
  9. ↑ Cox, Caroline (1997), "Fungicide Factsheet: Chlorothalonil", Journal of Pesticide Reform, 17 (4): 14–20
  10. ↑ Franz Müller, Peter Ackermann and Paul Margot "Fungicides, Agricultural, 2. Individual Fungicides" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.o12_o06
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