Ioxynil

Ioxynil

Names
IUPAC name 4-Hydroxy-3,5-diiodophenyl cyanide
Other names Iodoxynil, Ioxinil,
Identifiers
CAS Number	1689-83-4^Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:81821
ChEMBL	ChEMBL509523
ChemSpider	14774^Y
ECHA InfoCard	100.015.347
KEGG	C18546^Y
PubChem CID	15530
UNII	8Y734M4V9E
UN number	2588
CompTox Dashboard (EPA)	DTXSID8022161
InChI InChI=1S/C7H3I2NO/c8-5-1-4(3-10)2-6(9)7(5)11/h1-2,11H Key: NRXQIUSYPAHGNM-UHFFFAOYSA-N
SMILES C1=C(C=C(C(=C1I)O)I)C#N
Properties
Chemical formula	C7H3I2NO
Molar mass	370.916 g·mol^−1
Appearance	Crystalline colourless[1]
Odor	Phenol-like[1]
Melting point	212[1] °C (414 °F; 485 K)
Solubility in water	0.05 g/L [1]
Solubility in acetone	7 %w/v[2]
Solubility in dimethylformide	74 %w/v[2]
Solubility in ethanol	2 %w/v[2]
Solubility in cyclohexane	14 %w/v[2]
Solubility in tetrahydrofuran	34 %w/v[2]
Solubility in benzene	0.5 %w/v[2]
Vapor pressure	< 0.001 Pa [1]
Hazards
GHS labelling:[3]
Pictograms
Signal word	Danger
Hazard statements	H301, H319, H361, H410
Lethal dose or concentration (LD, LC):
LD50 (median dose)	110 mg/kg (rat, oral)[1]
LC50 (median concentration)	0.38 mg/L (rat, inhalation), 6.8 mg/L (fish)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Ioxynil is a post-emergent^[4] selective nitrile herbicide. It is used in Australia, New Zealand^[5] and Japan^[6] to control broadleaf weeds via the inhibition of photosynthesis. It is used notably on onion crops,^[7] among others, normally at 300–900 g/Ha.^[8] It was introduced in 1966. The supply of ioxynil is decreasing, as of 2019 but the herbicide remains effective.^[9]

History

Ioxynil and bromoxynil (along with 2,4-DB and MCPB) were patented by Louis Wain as joint-head of the chemistry department at Wye College,^[10] and coincidentally discovered independently by May & Baker in England screening spare nitriles for herbicide activity, and by Amchem Products Inc in America doing similar screening, all in 1963. Commercial prospects were promising, as cereals could tolerate large amounts, over 2 lbs/ac;^[11] even 4 lbs/ac only temporarily scorches.^[12]

Wain theorised ioxynil and bromoxynil, the nitrile (-CN) group herbicides, because of the chemical similarity to a nitro (NO₂) group, and on their success, the -SO₂CH₃ group was explored, leading to the discovery of methylsulphone herbicides.^{[10]: 448-450}

May & Baker, a subsidiary of Rhone-Poulenc began ioxynil's, and the very similar bromoxynil's, production in Norwich in 1965,^[13][2] where it has continued for over 40 years.^[14] By 1968, ioxynil (as "Buctril") was registered for use in the USA, Canada, the UK, Australia, New Zealand, Japan, the West Indies and most of Europe.^[2]

In the 2010s, ioxynil was produced in South Africa to alleviate shortages.^[15]

Regulations

Today, ioxynil is banned in the EU and used in Brazil,^[16] China (as octanoate),^[17] New Zealand,^[18] Australia, South Africa and Japan.^{[citation needed]}

The UK followed the EU's ban (taking effect 1 September 2015) to ban ioxynil's sale; the European approval lapsing under Regulation (EC) 1107/2009.^[19]

India and Columbia raised concerns about the EU's maximum allowed residue for ioxynil (amongst other pesticides), saying the EU's stance was too precautionary and not based on evidence, which is yet inconclusive on their genotoxicity.^[20] Bayer, Syngenta and others launched a lawsuit against the 2022 ban on exporting EU-prohibited pesticides from the EU to nations where they are legal, however the French Constitutional Court has upheld the ban.^[21]

Properties

Ioxynil is a flammable solid with a weak phenolic smell and decays under UV light.^[22] Ioxynil's octanoate, ioxynil octanoate, or 4-cyan-2,6-diiodphenyloctanoate, is likewise a colourless insoluble solid and hydrolyses to ioxynil in basic conditions.^[23]

The taste of ioxynil is "slight, not characteristic."^[2]

Mechanism and effect

Ioxynil acts via photosynthesis inhibition.^[7] It and bromoxynil uncouple oxidative phosphorylation and inhibit photosynthetic phosphorylation. Ioxynil additionally breaks down into iodide ions which inhibit plant growth again.^[10] Ioxynil may also inhibit photoreduction of ferricyanide, fixation of carbon dioxide, photoreduction of NAPD or of endogenous plastoquinone. Ioxynil acts as an electron transport inhibitor and uncoupling agent.^[2]

Symptoms on weeds appear after a few hours or days. Areas of collapsed tissue appear, rapidly becoming necrotic. In good conditions on small plants, necrosis may complete within two days but some weeds can take up to three weeks to die. Effectiveness is enhanced if any times of high humidity occur 1 or 2 days after application. Light and temperature speed up herbicidal action.^[2]

Ioxynil is a Group C, (Australia), C3 (Global) or Group 6, (numeric) resistance class herbicide.^[24]

Toxicology

Ioxynil is toxic to mammals, with an oral LD₅₀ of 110 mg/kg (rats), dermal LD₅₀ of 800 mg/kg, and inhalative LC₅₀ of 0.38 mg/L over four hours. Ioxynil is toxic to fish, with a 96 hour LC₅₀ of 6.8 mg/L, and 3.9 mg/L for daphnia.^[1] Plankton and bloodworms are also effected.^[25] The oral LD₅₀s in mice, guinea-pigs, rabbits and dogs respectively are 230, 76, 180, > 100 mg/kg.^[2]

Ioxynil can affect the human thyroid via binding to transthyretin, a thyroid hormone binding protein which transports thyroid hormone in the blood. It can provoke thyroid tumors in rats, and can disrupt zebrafish's heart development.^[6]

Environmental fate

Ioxynil is a contact herbicide and has no residual soil activity or translocation, so spray coverage must be thorough as unsprayed weeds will not be controlled;^[4] large enough weeds may even contain surviving portions that resprout, and resistance can occur at later growth stages.^[11] Translocated chemical may produce chlorosis but is unlikely to be lethal.^[2]

Ioxynil bioaccumulates, although it does not linger long in the environment.^[25] Ioxynil, bromoxynil, and their octanoate variants, leave negligible residues after use on crops. In all cases, under 0.01 ppm, the limit of detection, though some inactive content may be adsorbed into the soil.^[2]

Lists

Ioxynil is or has been sold under these tradenames: Ioxynil, Unyunox, Totril, Toxynil, Hawk, Hocks, Sanoxynil, Iotril, Certrol, Actril, Actrilawn, Bentrol, Belgran, Bronx, Cipotril, Dantril, Oxytril, Mextrol-Biox, Sanoxynil, Shamseer-2, Stellox, Iotox, Iconix and Trevespan. Some products include multiple active ingredients.^{[citation needed]}

Ioxynil has been sold in formulations also containing bromoxynil and isoproturon.^{[citation needed]}

It is used to control these weeds: bellvine, burr medic, capeweed, chickweed, climbing buckwheat, common heliotrope, common sowthistle, corn gromwell, dandelion, dead nettle, fat-hen, fumitory, green amaranth, green crumbleweed, bittercress, ox tongue, pigweed, potato weed, saffron thistle, scarlet pimpernel, shepherd's purse, slender celery, smallflower mallow, stagger weed, threecornered Jack, three flowered nightshade, turnip weed, Ward's weed, wild radish, wild turnip, wireweed,^[4] annual sowthistle, cornbind, musky storksbill, willow weed, buttercup, field pansy, groundsel, plantain, speedwell, stinking mayweed,^[5] the knotweed family broadly, in particular tartary buckwheat, the composite or sunflower family, chamomile, mayweed, some borages, fiddlenecks, gromwells^[2] and prickly paddy melon.^[7]

Crops situations which ioxynil has been used on include: onions, spring onions, welsh onions,^[26] garlic onions,^[5] cereals, leeks, garlic, shallots, flax, sugarcane, forage grasses, lawns and turf.^[27] Peas,^[12] oats, maize, sorghum and rice show high tolerance.^[11] Limited resistance is seen in lucerne, clover and carrot.^[12]

References

1. "Ioxynil SDS" (PDF). LGC. Retrieved 10 September 2024.
2. "Technical Bulletin Ioxynil and Bromoxynil Selective Herbicides". International Journal of Pest Management: Part C. 14 (3): 301–322. September 1968. doi:10.1080/05331856809438464.
3. "Safety Data Sheet: Genfarm Ioxynil 250 Herbicide" (PDF).
4. "Unyunox 250 EC" (PDF). AgNova.
5. "Iotril Label". Adama. 24 September 2021. Retrieved 10 September 2024.
6. Li, Yi-Feng; Canário, Adelino V. M.; Power, Deborah M.; Campinho, Marco A. (1 March 2019). "Ioxynil and diethylstilbestrol disrupt vascular and heart development in zebrafish". Environment International. 124: 511–520. Bibcode:2019EnInt.124..511L. doi:10.1016/j.envint.2019.01.009. hdl:10400.1/14569. PMID 30685453.
7. "Ioxynil 250 Label" (PDF). Genfarm.
8. "Herbicide Ioxynil For Grain Fields". www.ageruo.com. Ageruo biotech. Retrieved 10 September 2024.
9. "New herbicide in onions shows promise". www.farmcraft.com.au. Farmcraft. 13 August 2019. Retrieved 9 September 2024.
10. Fowden, Leslie (2002). "Ralph Louis Wain, C.B.E. 29 May 1911 – 14 December 2000". Biographical Memoirs of Fellows of the Royal Society. 48: 439–458. doi:10.1098/rsbm.2002.0026. S2CID 70562660.
11. Holly, K. (December 1964). "Ioxynil and Bromoxynil as Herbicides". International Journal of Pest Management: Part C. 10 (4): 256–258. doi:10.1080/05331856409432879.
12. Holly, K.; Holroyd, J. (November 1963). "3,5-Di-iodo-4-hydroxyhenzonitrile. A progress report on experimental work by the A.R.C. Weed Research Organisation May - October 1963" (PDF). Africultural Research Council. Begbroke Hill, Kidlington, Oxford: Weed Research Organisation.
13. "Briar Chemicals – Company Profile". www.w2bchemicals.com. Retrieved 10 September 2024.
14. "J300 AC Drive Case Study". HID Online. HID Hitachi Ltd. 2003. Retrieved 10 September 2024.
15. Lewis, Sophie (31 August 2018). "South Africa comes to rescue to ease herbicide shortage". The Weekly Times. Retrieved 10 September 2024.
16. Russau, Christian (27 April 2020). "Pesticides, Cancer, double standards, and what Bayer has to do with the Amazon's rainforest fires". Association of Ethical Shareholders Germany. Ethical Shareholders. Retrieved 10 September 2024.
17. "Total of 20 Pesticides Initially Registered in China in 2013". Grainews.
18. "DECISION" (PDF). Environmental Protection Authority of New Zealand. 6 May 2018.
19. "UK withdraws products containing ioxynil". AgNews. 19 November 2014. Retrieved 10 September 2024.
20. "U.S. voices concerns at WTO meeting on pesticides, tariffs, etc". Food Safety News. November 16, 2018. Retrieved 10 September 2024.
21. "Frankreich: Erfolg gegen Pestizid-Exporte \ Wegweisendes Urteil des höchsten Gerichts". radio dreyeckland 102.3. 10 February 2020. Retrieved 10 September 2024.
22. Record of Ioxyniloctanoat in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 2016-02-01.
23. Robert Irving Krieger (2001). Handbook of pesticide toxicology. Vol. 1. Academic Press. ISBN 978-0-12-426260-7.
24. "Australia Herbicide Classification Lookup". Herbicide Resistance Action Committee.
25. Mäenpää, Kimmo A; Sormunen, Arto J; Kukkonen, Jussi V. K (1 November 2003). "Bioaccumulation and toxicity of sediment associated herbicides (ioxynil, pendimethalin, and bentazone) in Lumbriculus variegatus (Oligochaeta) and Chironomus riparius (Insecta)". Ecotoxicology and Environmental Safety. 56 (3): 398–410. Bibcode:2003EcoES..56..398M. doi:10.1016/S0147-6513(03)00010-1. PMID 14575680. Retrieved 10 September 2024.
26. "Iconix Label" (PDF). Imtrade Australia Pty Ltd.
27. "Ioxynil". Pesticide Properties DataBase. Retrieved 8 September 2024.

External links

• Ioxynil in the Pesticide Properties DataBase (PPDB)