chlorothalonil

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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 reacts with glutathione giving an glutathione adduct with elimination of HCl. Its mechanism of action is similar to that of trichloromethyl sulfenyl fungicides{{Citation

| last1 = Tillman

| first1 = Ronald

| last2 = Siegel

| first2 = Malcolm

| last3 = Long

| first3 = John

| title = 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

| journal = Pesticide Biochemistry and Physiology

| volume = 3

| issue = 2

| pages = 160–167

| date = June 1973

| doi = 10.1016/0048-3575(73)90100-4

}} such as captan and folpet.{{cite journal |title= Reactions of certain trichloromethyl sulfenyl fungicides with low-molecular-weight thiols. In vivo studies with cells of Saccharomyces pastorianus |first= Malcolm R. |last= Siegel |journal= J. Agric. Food Chem. |year= 1970 |volume= 18 |issue= 5 |pages= 823–826 |doi= 10.1021/jf60171a034 |pmid= 5474238 }}

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.

International Agency for Research on Cancer IARC has assessed chlorothalonil as a Group 2B "possible 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.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. [http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0070182]

Chlorothalonil is highly toxic to fish and aquatic invertebrates, but not toxic to birds.[http://www.inchem.org/documents/ehc/ehc/ehc183.htm Environmental Health Criteria 183], World Health Organization, 1996.

At a concentration of 164 μg/L, chlorothalonil was found to kill a species of frog within a 24-hour exposure.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}}

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".

Chlorothalonil has been detected in ambient air Prince Edward Island,{{cite journal |vauthors = White LM, Ernst WR, Julien G, Garron C, Leger M |title=Ambient air concentrations of pesticides used in potato cultivation in Prince Edward Island, Canada |journal=Pest Manag. Sci. |volume=62 |issue=2 |pages=126–36 |year=2006 |pmid=16358323 |doi=10.1002/ps.1130}} 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. It has also been detected in several fish kills in Prince Edward Island.{{Cite web|url=https://www.princeedwardisland.ca/sites/default/files/publications/fish_kill_statistic_1962-2016.pdf|title=Island Fish Kills from 1962 to 2016|website=Government of PEI|access-date=12 December 2016}}

The main breakdown product of chlorothalonil is hydroxy-2,5,6-trichloro-1,3-dicyanobenzene (SDS-3701). It has been shown to be 30 times more acutely toxic than chlorothalonil and more persistent in the environment.{{cite journal |last1=Arena |first1=Maria |last2=Auteri |first2=Domenica |last3=Barmaz |first3=Stefania |last4=Bellisai |first4=Giulia |last5=Brancato |first5=Alba |last6=Brocca |first6=Daniela |last7=Bura |first7=Laszlo |last8=Byers |first8=Harry |last9=Chiusolo |first9=Arianna |last10=Court Marques |first10=Daniele |last11=Crivellente |first11=Federica |last12=De Lentdecker |first12=Chloe |last13=Egsmose |first13=Mark |last14=Erdos |first14=Zoltan |last15=Fait |first15=Gabriella |last16=Ferreira |first16=Lucien |last17=Goumenou |first17=Marina |last18=Greco |first18=Luna |last19=Ippolito |first19=Alessio |last20=Istace |first20=Frederique |last21=Jarrah |first21=Samira |last22=Kardassi |first22=Dimitra |last23=Leuschner |first23=Renata |last24=Lythgo |first24=Christopher |last25=Magrans |first25=Jose Oriol |last26=Medina |first26=Paula |last27=Miron |first27=Ileana |last28=Molnar |first28=Tunde |last29=Nougadere |first29=Alexandre |last30=Padovani |first30=Laura |last31=Parra Morte |first31=Juan Manuel |last32=Pedersen |first32=Ragnor |last33=Reich |first33=Hermine |last34=Sacchi |first34=Angela |last35=Santos |first35=Miguel |last36=Serafimova |first36=Rositsa |last37=Sharp |first37=Rachel |last38=Stanek |first38=Alois |last39=Streissl |first39=Franz |last40=Sturma |first40=Juergen |last41=Szentes |first41=Csaba |last42=Tarazona |first42=Jose |last43=Terron |first43=Andrea |last44=Theobald |first44=Anne |last45=Vagenende |first45=Benedicte |last46=Verani |first46=Alessia |last47=Villamar‐Bouza |first47=Laura |title=Peer review of the pesticide risk assessment of the active substance chlorothalonil |journal=EFSA Journal |date=January 2018 |volume=16 |issue=1 |pages=e05126 |doi=10.2903/j.efsa.2018.5126|pmid=32625673 |pmc=7009683 |doi-access=free }}{{Citation

|last = Cox

|first = Caroline

|title = Fungicide Factsheet: Chlorothalonil

|journal = Journal of Pesticide Reform

|volume = 17

|issue = 4

|pages = 14–20

|year = 1997

|url = http://www.pesticide.org/get-the-facts/pesticide-factsheets/factsheets/chlorothalonil

|archive-url = https://web.archive.org/web/20101110064601/http://www.pesticide.org/get-the-facts/pesticide-factsheets/factsheets/chlorothalonil

|archive-date = 10 November 2010}} Laboratory experiments have shown it can thin the eggshells of birds, but no evidence supports this happening in the environment.

In 2019, a review of the evidence found that "a high risk to amphibians and fish was identified for all representative uses", and that chlorothalonil breakdown products may cause DNA damage.{{cite web | last=Carrington | first=Damian | title=EU bans UK's most-used pesticide over health and environment fears | website=The Guardian | date=2019-03-29 | url=http://www.theguardian.com/environment/2019/mar/29/eu-bans-widely-used-pesticide-over-safety-concerns | access-date=2019-03-29}}{{Cite web | url=https://www.farminguk.com/news/European-Commission-votes-to-ban-fungicide-Chlorothalonil_51641.html | title=European Commission votes to ban fungicide Chlorothalonil}} Chlorothalonil and other fungicides are claimed to be the strongest factor in bumblebee population decline.

File:2,4,5-trichloro-6-hydroxyisophthalonitrile.svg|2,4,5-trichloro-6-hydroxy­isophthalonitrile (SDS-3701)

File:R417888.svg|Chlorothalonil sulfonic acid (R417888)

File:R471811.svg|R471811

Syngenta sued to stop communication by Swiss health authorities with the Swiss public regarding the "relevance" of specific metabolites of chlorothalonil that Swiss authorities detected in high concentrations in the groundwater from which hundreds of thousands of Swiss people obtain drinking water. The court banned Swiss health authorities from communicating with the public about the dangers posed by some of the metabolites.Le Monde, 27 Sept. 2022 [https://www.lemonde.fr/en/environment/article/2022/09/27/by-products-of-pesticide-banned-in-2019-found-in-swiss-drinking-water_5998346_114.html "By-Products of Pesticide Banned in 2019 Found in Swiss Drinking Water, Syngenta, The Producer of The Fungicide Chlorothalonil, Has Sued Swiss Health Authorities for Making Public The Danger Posed by Certain Derivatives of The Pesticide,"]

In March 2019, as a result of the previously mentioned research, the European Union banned the use of chlorothalonil dated to take effect May 20, 2020. Switzerland followed in December 2019.{{cite news |title=Swiss ban widely-used pesticide over health and environment fears |url=https://www.swissinfo.ch/eng/chlorothalonil_swiss-ban-widely-used-pesticide-over-health-and-environment-fears/45429716 |access-date=12 December 2019 |work=swissinfo |language=en}}

Chlorothalonil can be produced by the direct chlorination of isophthalonitrile or by dehydration of tetrachloroisophthaloyl amide with phosphoryl chloride.{{Ullmann |author=Franz Müller |author2=Peter Ackermann |author3=Paul Margot |title=Fungicides, Agricultural, 2. Individual Fungicides|doi=10.1002/14356007.o12_o06}} 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 dioxins and hexachlorobenzene, a persistent organic pollutant banned under the Stockholm Convention.

{{reflist|refs=

{{cite web | author=National Farmers' Union of England and Wales | title=Chlorothalonil use-by date approaching | website=NFU Online | url=http://www.nfuonline.com:443/sectors/crops/crops-news/chlorothalonil-use-by-date-approaching/ | access-date=2021-03-16}}

}}

• [http://extoxnet.orst.edu/pips/chloroth.htm Extension Toxicology Network: Chlorothalonil Pesticide Information Profile]
• {{PPDB|150}}
• {{cite web | title=2017 Pesticide Use Maps - Low | website=Water Resources | publisher=United States Geological Survey | url=http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2017&map=CHLOROTHALONIL&hilo=L | access-date=2021-03-16}}
• {{cite web | title=2017 Pesticide Use Maps - High | website=Water Resources | publisher=United States Geological Survey | url=http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2017&map=CHLOROTHALONIL&hilo=H | access-date=2021-03-16}}

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Category:Fungicides

Category:Nitriles

Category:Chloroarenes

Category:IARC Group 2B carcinogens