Paraquat

from Wikipedia, the free encyclopedia
Structural formula
Structural formula of paraquat
General
Surname Paraquat
other names
  • 1,1'-dimethyl-4,4'-bipyridinium
  • Methyl viologen
Molecular formula C 12 H 14 Cl 2 N 2
Brief description

colorless solid

External identifiers / databases
CAS number
  • 4685-14-7
  • 1910-42-5 (dichloride)
  • 2074-50-2 (dimethyl sulfate)
EC number 217-615-7
ECHA InfoCard 100.016.015
PubChem 15938
Wikidata Q409669
properties
Molar mass 186.3 g mol −1 (paraquat cation)
Physical state

solid (salts of the pure substance)

density

1.24 g cm −3

Melting point

Decomposes at 300 ° C

solubility
  • easy in water (620 g l −1 )
  • low in organic solvents
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary

Dichloride

06 - Toxic or very toxic 08 - Dangerous to health 09 - Dangerous for the environment

danger

H and P phrases H: 301 + 311-315-319-330-335-372-410
P: 260-273-280-284-301 + 310-305 + 351 + 338
MAK

Switzerland: 0.1 mg m −3 (measured as inhalable dust )

Toxicological data
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Paraquat is a quaternary ammonium compound from the bipyridine herbicide family that is used as a contact herbicide . Paraquat was developed by the English company Imperial Chemical Industries (whose agricultural division is now part of the Swiss company Syngenta ) in 1955 and was first marketed in 1962 under the trade name Gramoxone. Syngenta dominates the $ 1 billion global paraquat business, with an estimated 40 percent market share, or about $ 400 million.

synthesis

Paraquat can be obtained by reacting 4,4'-bipyridine and methyl chloride . The former is created by coupling pyridine with sodium in liquid ammonia and dehydration with oxygen.

Synthesis of paraquat

properties

Oxidation / reduction of paraquat

In aqueous solutions, the paraquat cation takes up electrons in a reversible reaction . The resulting radical colors the solution a strong purple, which is why the substance is sometimes referred to as methyl viologen .

Mode of action

Z-diagram of photosynthesis with possible points of attack for herbicides, paraquat top right.

Paraquat is absorbed very quickly through plant surfaces, especially in warm and humid climates. In the chloroplasts , electrons are transferred from photosystem I to the paraquat cation , which then becomes a paraquat radical. The radical releases its excess electron to an oxygen molecule, creating hyperoxide . Hyperoxides are very reactive chemically and destroy unsaturated fatty acids in the chloroplast and cell membranes . Since the cation is repeatedly reduced to a radical by electrons, this process continues until the photosystem is destroyed. The cell membrane becomes porous and water is lost. The plants dry up within a few hours in sunny weather.

use

Plant protection

Usage in the USA

Paraquat is used against broad-leaved plants and grasses. Since it does not penetrate the bark of trees, it can be used for weed control in orchards and vineyards as well as in coffee , tea , oil palm or banana plantations , for example. Despite its frequent use, there are few cases of paraquat resistance in weeds.

Because of its high toxicity , paraquat has long been banned in the EU and Switzerland. Paraquat is still used in the USA, but is gradually being phased out in China.

Further areas of application

In South Africa, fire breaks are kept clear with the help of paraquat in order to prevent forest and bush fires . Paraquat is also used to allow plant material to dry faster. For example, it means that crop residues dry faster after growing pineapples and can be burned sooner.

Experimental medicine

Paraquat as MPP + and for induction of Parkinson's disease used in experimental model systems.

Environmental impact

The toxicity for fish depends on the type of fish and the hardness of the water ; a bioaccumulation is not observed in aquatic animals.

In the soil, paraquat is well absorbed by clay minerals and humus and is therefore hardly washed out. Due to the strong adsorption, the damaging effect of paraquat is buffered, on the other hand it can remain in the soil for many years. The half-life ( DT 50 value ) is given by the FAO as 1000 days. On the other hand, paraquat residues are rapidly decomposed on the surface of plants and under the influence of light.

Paraquat is not dangerous to bees; For birds Paraquat seems to be only moderately toxic.

Paraquat easily adsorbs on surfaces ( sediment , suspended matter ) and is only slowly degraded.

Admission

Paraquat is approved in around 100 countries worldwide (including the USA, Canada, Australia, Japan, New Zealand) and is now banned in over fifty nations, in Switzerland since 1989, in the EU since 2007. In Switzerland, Syngenta had claimed paraquat for years to have withdrawn from the market due to lack of demand. The Federal Council contradicted this representation in 2002. The non-governmental organization Declaration of Bern published an interview in 2011 with Urs Niggli , who was responsible for the approval at the Wädenswil Research Station . According to this, Maag AG (now Syngenta) tried to bring Paraquat back onto the market in Switzerland in the 1980s. The research institute in Wädenswil rejected the application for toxicological and ecotoxicological reasons. After the major fire in Schweizerhalle , Maag AG withdrew its objection to this decision.

On July 11, 2007, the European Court of Justice revoked the approval guideline for paraquat in the first instance. In October 2007, Syngenta prepared a reauthorisation application. In February 2009, Syngenta decided not to submit a new application for economic reasons. On April 1, 2011 the “Chemical Review Committee” of the UNEP / FAO Rotterdam Convention approved the inclusion of Gramoxone ® Super (active substance: 200 g Paraquat / L) in the “Prior Informed Consent (PIC) procedure” of Rotterdam -Convention recommended. However, the PIC list was blocked by Guatemala and India at the Conference of the Parties in March / April 2013. The discussion was postponed to the next Conference of the Parties in 2015. Since then, the decision has been postponed so that the subject will be the subject of the next Conference of the Parties in 2021.

A legal opinion from 2011, which was carried out on behalf of the European Center for Constitutional and Human Rights (ECCHR) and the Bern Declaration (EvB), concluded that Syngenta disregarded elementary human rights by selling its herbicide paraquat in developing countries . This practice still exists (as of 2019).

In 2017, Brazil decided to ban paraquat due to its harmful effects on health with a three-year transition period.

toxicology

The LD 50 in rats is 57–87 mg / kg body weight, for humans the LD 50 is estimated at 35 mg / kg body weight. Paraquat leads to many fatal cases of poisoning. It used to be sold as a reddish-brown, odorless solution. If this was poured into empty beverage bottles, it could be mistaken for cola drinks or red wine. In addition, paraquat is often used by suicides . Since the mid-1970s, paraquat formulations have mostly, but not always, been added to a conspicuous blue dye, a substance with a pungent odor and a fast-acting emetic as a preventive measure . The first symptoms of paraquat poisoning are often a severe burning sensation in the mouth and throat, pain in the abdomen, loss of appetite , dizziness , vomiting and diarrhea . In addition to shortness of breath , rapid heart rate , kidney failure , pain in the lung may occur and damage the liver.
In the case of paraquat poisoning, the administration of oxygen must be carefully considered, as it leads to fibrosis of the lungs. The reason for this is the accumulation of paraquat in the lung tissue. The oxygen regenerates the paraquat through oxidation and at the same time leads to the formation of hydrogen peroxide radicals, which primarily damage the lungs, but also the liver and kidneys. For this reason, antioxidants play a prominent role in paraquat toxicity.
Ingestion of a lethal dose leads to cramps , incoordination and ultimately irreversible pulmonary fibrosis . Death occurs after a few days, sometimes even after several weeks.

According to the WHO , the permitted daily dose is 0.004 mg / kg body weight. In the case of poisoning by paraquat, the immediate administration of activated charcoal is recommended, later increased diuresis , in the early stages also hemoperfusion . In addition to primary and secondary poison elimination, symptomatic therapy is of particular importance. There is no antidote .

The US Environmental Protection Agency (EPA) has classified paraquat as potentially carcinogenic and weakly mutagenic . A teratogenic effect can occur at high doses .

The use of paraquat preparations by small farmers in developing countries , who often use pesticides without the necessary protective measures, is problematic . The resources are often stored improperly, no protective clothing is worn or even barefoot and non-body covering clothing is worked, children are present while working in the fields and minimum distances to bodies of water are insufficient or not kept at all. The consequences are sometimes severe and chronic illnesses. One reason for improper use is that the instructions for use are incomprehensible for many users because they cannot read or speak a different language. Development organizations accuse the manufacturers of not working to improve the situation, as this could affect sales.

Trivia

Paraquat murders in Japan

In 1985, at least twelve people in Fukuyama and Hiroshima were poisoned with drinks that had been poisoned with paraquat by an unknown perpetrator. The modus operandi was always the same: apparently unobjectionable beverage cans were left on top of beverage machines or in the machine, which killed their finders with the tasteless paraquat they contained.

After twelve people were killed in this way, warnings were attached to the machines by many machine operators, urging them against drinking from abandoned cans. No further poisoning occurred after these warnings were published. The perpetrator or perpetrators were never caught.

Web links

Individual evidence

  1. ↑ Entry on paraquat dichloride. In: Römpp Online . Georg Thieme Verlag, accessed on April 13, 2014.
  2. ↑ a b c EXTOXNET: Substance and toxicity data .
  3. ↑ a b c d e f g h i j Entry on paraquate dichloride in the GESTIS substance database of the IFA , accessed on January 9, 2019(JavaScript required) .
  4. ↑ Entry on paraquat dichloride in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  5. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for paraquat dichloride ), accessed on November 25, 2019.
  6. ↑ a b Public Eye: How much longer paraquat? November 2017; accessed on December 11, 2017.
  7. ↑ Public Eye : Paraquat ; accessed on December 11, 2017.
  8. ↑ Directorate-General for Health and Food Safety of the European Commission: Entry on paraquat in the EU pesticide database; accessed on December 11, 2017.
  9. ^ Paraquat: A controversial chemical's second act. In: Reuters . April 2, 2015, accessed July 29, 2016 .
  10. ^ B. Streit: Uptake, accumulation and release of organic pesticides by benthic invertebrates. 2. Reversible accumulation of lindane, paraquat and 2,4-D from aquous solution by invertebrates and detritus. In: Arch. Hydrobiol. Suppl. 55, 1979, pp. 324-348.
  11. ↑ Fact sheets on pesticides (accessed January 11, 2009).
  12. ↑ Regulation (English).
  13. ↑ Public Eye: Paraquat ban in Switzerland: How Syngenta tries to twist unpleasant facts. October 18, 2011; accessed on December 11, 2017.
  14. ↑ Federal Office for Consumer Protection and Food Safety : Technical reports - BVL suspends approval for paraquat-containing pesticides. July 18, 2017, accessed October 11, 2019 .
  15. ^ Court of First Instance of the European Communities: Press release No. 45/07 (PDF file; 106 kB). July 11, 2007.
  16. ↑ Syngenta media release: Syngenta is preparing a new EU approval application for paraquat ( memento of January 14, 2010 in the Internet Archive ). October 9, 2007.
  17. ↑ Viewpoint on paraquat withdrawal in Europe ( Memento of December 11, 2010 in the Internet Archive ) (English).
  18. ↑ UN press release: Pesticides and industrial chemicals recommended for trade “watch list”. April 1, 2011, accessed May 22, 2011 .
  19. ^ Paraquat at the Rotterdam Convention - Paraquat Information Center. Retrieved October 11, 2019 .
  20. ^ Pesticide Action Network North America: Guatemala and India block listing of toxic paraquat formulation in the Rotterdam Convention. May 9, 2013, accessed September 4, 2013 .
  21. ^ Declaration by Bern and ECCHR: The Distribution of Paraquat: Does Syngenta Respect Human Rights? (PDF file; 527 kB).
  22. ↑ Stefan Häne: Too toxic for Switzerland - but exportable anyway. In: derbund.ch . March 15, 2019, accessed March 16, 2019 .
  23. ↑ Public Eye: Brazil bans paraquat - lobby is formed. October 23, 2017; accessed on December 11, 2017.
  24. ↑ Einar Göhring: The paraquat poisoning . epubli Berlin, 2017, ISBN 978-3-7375-4269-2 .
  25. ↑ Ashish Goel, Praveen Aggarwal: Pesticide poisoning . In: The National Medical Journal of India . tape 20 , no. 4 , August 1, 2007, p. 182-191 , PMID 18085124 .
  26. ↑ James S. Bus, James E. Gibson: Paraquat. Model for oxidant-initiated toxicity . In: Environmental Health Perspectives . tape 55 . National Institute of Environmental Health Sciences, April 1984, pp. 37-36 , PMID 6329674 , PMC 1568364 (free full text).
  27. ↑ Zacharias E. Suntres: Role of antioxidants in paraquat toxicity . In: Toxicology . tape 180 , no. 1 , October 30, 2002, p. 65-77 , doi : 10.1016 / s0300-483x (02) 00382-7 ( PDF ).
  28. ↑ Clyde Haberman: Japanese Puzzle: the Vending Machine Murders . In: The New York Times . December 10, 1985 ( nytimes.com ).