Diquat is the
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
common name
In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...
for an
organic dication that, as a
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
with
counterion
160px, Polystyrene sulfonate, a cation-exchange resin, is typically supplied with as the counterion.">cation-exchange_resin.html" ;"title="Polystyrene sulfonate, a cation-exchange resin">Polystyrene sulfonate, a cation-exchange resin, is typical ...
s such as
bromide
A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...
or
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
is used as a contact
herbicide
Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
that produces
desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container.
...
and
defoliation
A defoliant is any herbicidal chemical sprayed or dusted on plants to cause their leaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, along with the ...
. Diquat is no longer approved for use in the
European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
, although its
registration
Register or registration may refer to:
Arts entertainment, and media Music
* Register (music), the relative "height" or range of a note, melody, part, instrument, etc.
* ''Register'', a 2017 album by Travis Miller
* Registration (organ), th ...
in many other countries including the USA is still valid.
Synthesis
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...
is oxidatively coupled to form
2,2′-bipyridine
2,2′-Bipyridine (bipy or bpy, pronounced ) is an organic compound with the formula C10H8N2. This colorless solid is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals ...
over a heated
Raney nickel catalyst. The ethylene bridge is formed by the reaction with
1,2-dibromoethane
1,2-Dibromoethane, also known as ethylene dibromide (EDB), is an organobromine compound with the chemical formula . Although trace amounts occur naturally in the ocean, where it is formed probably by algae and kelp, it is mainly synthetic. It is a ...
:
History
Diquat's herbicidal properties were recognized in 1955 in the
Imperial Chemical Industries
Imperial Chemical Industries (ICI) was a British chemical company. It was, for much of its history, the largest manufacturer in Britain.
It was formed by the merger of four leading British chemical companies in 1926.
Its headquarters were at M ...
(ICI) laboratories at
Jealott's Hill
Jealott's Hill is a village in the county of Berkshire, England, within the civil parish of Warfield. The settlement is on the A3095 road approximately north of Bracknell. The nearest railway station is in .
The name of the hill is reported to ...
, following its first synthesis at ICI's Dyestuffs Division in Blackley, England.
It was active on test plants at application rates as low as 0.1 lb/acre. It was found that only those quaternary salts which were capable of being converted by reducing agents to radical cations had herbicidal activity and another of these was
paraquat
Paraquat (trivial name; ), or ''N'',''N''′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is an organic compound with the chemical formula C6H7N)2l2. It is classified as a viologen, a family of redox ...
, which was more effective as a non-selective herbicide than diquat.
Initial attempts to commercialize diquat focused on its ability to control
broadleaved
A broad-leaved, broad-leaf, or broadleaf tree is any tree within the diverse botanical group of angiosperms that has flat leaves and produces seeds inside of fruits. It is one of two general types of trees, the other being a conifer, a tree with n ...
annual weeds while damage to cereal crops was, by comparison, minor. However, the
auxin
Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...
herbicides including ICI's
MCPA
MCPA (2-methyl-4-chlorophenoxyacetic acid) is a powerful, selective, widely used phenoxy herbicide. The pure compound is a brown-colored powder. MCPA has been extensively used in agriculture to control broad-leaf weeds as a growth regulator prima ...
were more selective and hence this use of diquat was unattractive.
Instead, diquat was combined with the use of specialised mechanised equipment which by the late 1950s was becoming common in the harvesting of crops such as potatoes. A concern in that use was the possibility that the compound could cause
stem-end rot, but protocols were developed that overcame this problem and it was introduced commercially for potato haulm desiccation in 1961.
In the mid 1960s, diquat's use was extended to the pre-harvest desiccation of oilseed crops such as sunflower, linseed, cotton and soya.
The patent to the active ingredient has now expired in all countries.
Mode of action
When acting as a herbicide, diquat inhibits photosynthesis. In light-exposed plants, it accepts an electron from
photosystem I
Photosystem I (PSI, or plastocyanin–ferredoxin oxidoreductase) is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I is an integral membrane protein complex that uses ...
(more specifically
ferredoxin
Ferredoxins (from Latin ''ferrum'': iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied t ...
), to form its green radical cation:
:
iquatsup>2+ + e
− iquatsup>+•
The electron is then transferred to molecular oxygen, producing destructive
reactive oxygen species
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.
The reduction of molecular oxygen () p ...
. In forming these, the diquat dication is regenerated and is again available to shunt electrons from photosystem I to restart the cycle.
Formulation
Diquat is made available to end users only in
formulated products. Since it has extremely high solubility in water modern formulations contain up to 40% of the active dibromide salt.
Usage
All pesticides are required to seek registration from appropriate authorities in the country in which they will be used.
In the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, the
Environmental Protection Agency
A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...
(EPA) is responsible for regulating pesticides under the
Federal Insecticide, Fungicide, and Rodenticide Act
The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) is a United States federal law that set up the basic U.S. system of pesticide regulation to protect applicators, consumers, and the environment. It is administered and regulated by t ...
(FIFRA) and the
Food Quality Protection Act
The Food Quality Protection Act (FQPA), or H.R.1627, was passed unanimously by Congress in 1996 and was signed into law by President Bill Clinton on August 3, 1996. The FQPA standardized the way the Environmental Protection Agency (EPA) would man ...
(FQPA).
A pesticide can only be used legally according to the directions on the label that is included at the time of the sale of the pesticide. The purpose of the label is "to provide clear directions for effective product performance while minimizing risks to human health and the environment". A label is a legally binding document that mandates how the pesticide can and must be used and failure to follow the label as written when using the pesticide is a federal offense.
Within the European Union, a 2-tiered approach is used for the
approval and authorisation of pesticides. Firstly, before a formulated product can be developed for market, the active substance must be approved for the European Union. After this has been achieved, authorisation for the specific product must be sought from every Member State that the applicant wants to sell it to. Afterwards, there is a monitoring programme to make sure the pesticide residues in food are below the limits set by the
European Food Safety Authority
The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...
. Although diquat was used in many European countries from the 1960s, an EU directive has removed its approval for any use, effective from 12 October 2018.
Diquat is an unusual herbicide because it is often not used for weed control but is instead applied directly on mature crops. This causes desiccation, making the crop easier to harvest, particularly with mechanised equipment. The advantage to the farmer can be to advance the harvesting date, reduce the time taken to harvest and, in the case of seed crops, reduce the moisture content of the seed and increase its useful yield.
Farmers can act in their best economic interest: the value of these benefits can be estimated and the total cost of using the herbicide, including the cost, for example of aerial spraying, informs the decision to purchase. This
cost-benefit analysis by the end user sets a maximum price which the supplier can demand. When used as a conventional herbicide for weed control, diquat must be applied after the weeds have emerged since it is only effective on contact with green tissue. In this use it is fast-acting in sunlight and more effective on broadleaved weeds than grasses.
Mixing of diquat with other herbicides is also feasible.
The estimated annual use of diquat in US agriculture is mapped by the US Geological Survey. This shows that use is fairly stable and in 2018, the latest date for which figures are available, was about annually, almost exclusively in fruit and vegetable crops.
Beyond agriculture, diquat is also used to control invasive species such as submerged aquatic vegetation in the California Delta. Because California public drinking water is drawn through the delta as part of the California State Water Project, trace amounts of this pesticide are in much of the state's water supply.
Human safety
Diquat dibromide is moderately toxic. It may be harmful to humans if swallowed, inhaled, or absorbed through the skin in large quantities.
Its chronic neurotoxic effects have been investigated.
First aid measures are included with the label information.
The
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) and
Food and Agriculture Organization
The Food and Agriculture Organization of the United Nations (FAO)french: link=no, Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is an intern ...
(FAO) joint meeting on pesticide residues has determined that the
acceptable daily intake
Acceptable daily intake or ADI is a measure of the amount of a specific substance (originally applied for a food additive, later also for a residue of a veterinary drug or pesticide) in food or drinking water that can be ingested (orally) daily ove ...
for diquat (as its ion) is 0-0.006 mg/kg bodyweight per day, with an acute
reference dose A reference dose is the United States Environmental Protection Agency's maximum acceptable oral dose of a toxic substance.Reference doses are most commonly determined for pesticides. The EPA defines an oral reference dose (abbreviated RfD) as:
es ...
of 0.8 mg/kg bodyweight. The
Codex Alimentarius
The Codex Alimentarius () is a collection of internationally recognized standards, codes of practice, guidelines, and other recommendations published by the Food and Agriculture Organization of the United Nations relating to food, food production ...
database maintained by the FAO lists the maximum residue limits for diquat in various food products.
Effects on the environment
Diquat bonds strongly to mineral and organic particles in soil and water, where it remains without significant degradation for years. However, bound to clays, diquat is biologically inactive at the concentrations typically observed in agricultural soils.
Brands
By international convention and in many countries the law, pesticide labels are required to include the common name of the active ingredients. These names are not the exclusive property of the holder of any patent or
trademark
A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from others ...
and as such they are the easiest way for non-experts to refer to individual chemicals. Companies selling pesticides normally do so using a brand name or
wordmark
__notoc__
A wordmark, word mark, or logotype, is usually a distinct text-only typographic treatment of the name of a company, institution, or product name used for purposes of identification and branding. Examples can be found in the graphic iden ...
which allows them to distinguish their product from competitor products having the same active ingredient. In many cases, this branding is country and formulation-specific so after several years of sales there can be multiple brand names for a given active ingredient. The situation is made even more complicated when companies license their ingredients to others, as is often done. The licensee will normally wish to create their own set of trademarks for use in advertising and to promote to their customers. In addition, they may intend to mix the licensed product with their own proprietary materials and would certainly create a new brand for these mixtures.
It is therefore difficult to provide a comprehensive list of brand names for products containing diquat in its many salt and ester forms. The original ICI brand was Reglone and this name is still used by
Syngenta
Syngenta AG is a provider of agricultural science and technology, in particular seeds and pesticides with its management headquarters in Basel, Switzerland. It is owned by ChemChina, a Chinese state-owned enterprise.
Syngenta was founded in 2 ...
. Other names include Aquacide, Dextrone, Preeglone, Deiquat, Spectracide, Detrone, Tribune and Weedtrine-D.
See also
*
Paraquat
Paraquat (trivial name; ), or ''N'',''N''′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is an organic compound with the chemical formula C6H7N)2l2. It is classified as a viologen, a family of redox ...
References
Further reading
*
*
*
External links
*
*
{{Herbicides
Hepatotoxins
Herbicides
Nitrogen heterocycles
Quaternary ammonium compounds
Desiccants
Heterocyclic compounds with 3 rings
Nephrotoxins