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Isoproturon

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Isoproturon (IPU) is a urea class selective herbicide, which has been used to control annual grasses and many broad leafed weeds in wheat, barley, rye and triticale.[5]

Isoproturon
Names
IUPAC name
1,1-dimethyl-3-(4-propan-2-ylphenyl)urea [2]
Other names
IPU, ipuron[1]
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.047.108 Edit this at Wikidata
EC Number
  • 251-835-4
KEGG
UNII
  • InChI=1S/C12H18N2O/c1-9(2)10-5-7-11(8-6-10)13-12(15)14(3)4/h5-9H,1-4H3,(H,13,15)
    Key: InChIKey=PUIYMUZLKQOUOZ-UHFFFAOYSA-N
  • N(C(N(C)C)=O)C1=CC=C(C(C)C)C=C1
Properties
C12H18N2O
Molar mass 206.289 g·mol−1
Appearance Colourless Crystals[1]
Density 1160 kg/m3[1]
Melting point 158[3] °C (316 °F; 431 K)
Boiling point 353[4] °C (667 °F; 626 K)
65 mg/L (22°C)[5]
Solubility in acetone 38 mg/L[1]
Solubility in methanol 75 mg/L[1]
Solubility in benzene 5 mg/L[1]
Solubility in xylol 4 mg/L[1]
Solubility in n-hexane 0.2 mg/L[1]
Vapor pressure 3.3 μPa (20°C),[5] 31.5 mPa (77°C)[1]
Hazards
GHS labelling:[6]
GHS08: Health hazardGHS09: Environmental hazard
H351, H373, H410
P203, P260, P261, P271, P273, P280, P304+P340, P317, P318, P319, P391, P405, P501
Lethal dose or concentration (LD, LC):
3350 mg/kg (mice, oral)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Isoproturon was introduced in 1971[7] by Hoechst AG, (now AgrEvo GmbH), Rhône-Poulenc and Ciba-Geigy AG.[1] It was once one of the most widely used herbicides in the world, however it has suffered various bans, notably in the USA in the late 1900s, and until 2016 was sold in 22 European countries.[8]

Regulatory Status

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IPU is used in India.[9]

United Kingdom

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Isoproturon was banned in March 2007, taking effect in July 2009, due to its effects on the aquatic environment.[10] New registration is pending in the UK for low-dose formulations.[7]

European union

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Isoproturon's registration in the European Union is expired, though under EC Regulation 1107/2009 it is approved in the Netherlands and no other EU member nation.[7] The EU's ban took effect from the 30th of September 2016.[11]

The EU Commission, that also banned amitrole, did so only partially on endocrine disruption concerns, and other unclear grounds. If it had been for only endocrine disruption, it is likely exemptions would be available (for 'serious danger to plant health' or 'negligible exposure') under EU law.[11] The European Court of Justice ruled in December 2015 that the commission illegally broke their "clear, precise and unconditional obligation" to publish scientific criteria.[12]

Australia

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Isoproturon was never registered in Australia. Agronomist Bill Crabtree estimates potential A$47 billion savings if IPU had been available since 1980. Trials to register IPU were ongoing in 2023.[13][14]

United States

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Isoproturon is not registered in the United States.

Formulation and Usage

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Technical grade isoproturon is >97% pure, and is then sold in commercial formulations, usually as an SC, suspended concentrate, or WP, wettable powder.[1]

Weeds controlled by IPU include annual grasses, such as black-twitch, common windgrass, common wild oat, and annual meadow grass. It is used in spring and winter to control many annual broad leaved weeds, such as wheat, rye, barley, triticale,[1] sugarcane, citrus, cotton and asparagus.[9] It is not used on durum wheat because of isoproturon's phytotoxicity to it, however it is nonphytotoxic to other cereals.[1]

Isoproturon's herbicide resistance class is class C2 (HRAC) or class 7 (WSSA). Black-twitch and lesser canary grass have shown resistant examples.[7]

Degradation

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Isoproturon is non-persistent in soil; very photochemically stable, and stable to acids and alkalis,[1] but under sustained ultraviolet light can degrade into some eleven products,[5] and can be hydrolytically cleaved by strong bases on heating.[1]

Degradation is mainly N-demethylation and oxidation of the ring-isopropyl group. Variations in order give rise to a few possible pathways, and the balance of demethylation and oxidation can allow selective activity of the herbicide. Both reactions may occur, making a typical degradation product of 2-(4-Aminophenyl)propan-2-ol (also called Dimethyl-p-Aminobenzylalkohol),[5] which is an irritant and may be harmful if swallowed.[15]

Most isoproturon is expected to have degraded in soil after 6-28 days; the rate is temperature sensitive as the process is driven by enzymes and microbes.[1] In water, the DT50 is 40 days, and and in water sediments 149 days.[7]

Metabolism in plants usually follows the path beginning with isopropyl side chain oxidation.[5]

Safety and Ecotoxicity

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Isoproturon is in the WHO's toxicity class III: Slightly Hazardous. The oral LD50 is 3350 mg/kg (mice), and percutaneously for rats is >2000 mg/kg. It is non-irritating to skin and eyes, as tested on rabbits. A dietary NOEL over 90 days for rates is 80 mg/kg, for dogs 50 mg/kg.[1] IPU is an endocrine disruptor.[7]

Isoproturon is not toxic to bees and birds but can harm fish, with LC50 of 191 mg/L (carp), guppies 91 mg/L, and catfish just 9 mg/L.[1] The UK Environment Agency set a non-statutatory acceptable average water limit of 2 µg/L or 20 µg/L in one measurement.[7] In rats, the half life of ingested isoproturon is about 8 hours, excretion being 86% through urination.[5]

Tradenames

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  • Isoproturon
  • Alon (AgrEvo)
  • Arelon (AgrEvo)
  • Avanon (Gharda)
  • Isoguard (Gharda)
  • Graminon (Ciba-Geigy AG)
  • Phytosanitaire (Rhone-Poulenc)
  • Tolkan (Rhone-Poulenc)

References

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  1. ^ a b c d e f g h i j k l m n o p q r s Tomlin, Clive (1994). The Pesticide Manual Incorporating the Agrochemicals Handbook (Tenth ed.). State Library of Western Australia: The Royal Society of Chemistry. p. 611. ISBN 0-948404-79-5.
  2. ^ "Isoproturon". Pubchem.
  3. ^ "CAS Common Chemistry". Retrieved 23 August 2024.
  4. ^ "About Isoproturon". ChemNet.com. Retrieved 24 August 2024.
  5. ^ a b c d e f g Roberts, Terry (1998). Metabolic pathways of agrochemicals: Part 1, Herbicides and plant growth regulators. Cambridge: Royal Society of Chemistry. ISBN 978-0-85404-494-8. Retrieved 23 August 2024.
  6. ^ "Hazardous Chemical Information System". SafeWork Australia. Retrieved 23 August 2024.
  7. ^ a b c d e f g "Isoproturon". Pesticide Properties DataBase. Retrieved 24 August 2024.
  8. ^ Leoci, Raffaella; Ruberti, Marcello (12 October 2020). "Isoproturon: A Controversial Herbicide Hard to Confine in a Global Market". Journal of Sustainable Development. 13 (6): 43. doi:10.5539/jsd.v13n6p43. Retrieved 12 August 2024.
  9. ^ a b Liu, Jing (1 January 2010). "Chapter 80 - Phenylurea Herbicides". Hayes' Handbook of Pesticide Toxicology (Third Edition): 1725–1731. doi:10.1016/B978-0-12-374367-1.00080-X. ISBN 978-0-12-374367-1.
  10. ^ Lawson, Alex. "Isoporturon ban comes in". Fresh Produce Journal. Retrieved 24 August 2024.
  11. ^ a b Neslen, Arthur (19 April 2016). "Europe bans two endocrine-disrupting weedkillers". The Guardian. Retrieved 24 August 2024.
  12. ^ "Judgment in Case T-521/14 Sweden v Commission" (PDF). PRESS RELEASE No 145/15. General Court of the European Union. 16 December 2015.
  13. ^ "4farmers instagram". 4Farmers Australia. Retrieved 24 August 2024.
  14. ^ Nicoletti, John; Crabtree, Bill (19 January 2024). "The lack of Isoproturon hurts wheat farmers". Farm Weekly. Retrieved 24 August 2024.
  15. ^ "C & L Inventory". European Chemicals Agency. Retrieved 23 August 2024.
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  • Isoproturon in the Pesticide Properties DataBase (PPDB)
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