PARAQUAT

Emetic
PP796, 2-amino-4, 5-dihydro-6-methyl-4-propyls-triazole-[1,5-a]pyrimidin-5-one
(FAO 2008)
Its molecular formula is: C 9 H 13 N 5 O. No
information could be found about its health
effects other than causing vomiting.
Contaminants
Free 4,4’-bipyridyl; terpyridines (FAO 2008)
4,4’-bipyridyl is the precursor of paraquat and
there is evidence linking it to skin cancer (see
Toxicology, Cancer). Little information appears to
be available on the health effects of terpyridines.
1.3 Metabolites
Paraquat is excreted largely unmetabolised,
along with small quantities of monoquat (1.9%),
paraquat monopyridone (3.2%), and paraquat
dipyridone (1.1%) (INCHEM 1986).
1.4 Mode of action in weeds
Paraquat is a fast-acting, non-selective
contact herbicide that is absorbed by the
foliage. It destroys plant tissue by disrupting
photosynthesis and rupturing cell membranes,
which allows water to escape leading to rapid
desiccation of foliage (Dinis-Olivera et al 2006).
It can also be translocated within the plant,
increasing the likelihood of residues.
1.5 Uses
Paraquat is used as a herbicide, desiccant,
defoliant, and plant growth regulator (US EPA
1997). It is used for controlling broadleaf weeds
and grasses in more than 100 different crops,
including plantations (Paraquat Information
Centre 2010a). According to industry sources,
between 1995 and 2001 3.9% of total global
sales were to oil palm plantations, 3.1% to
banana plantation and 2.5% to tea estates – in
all 9.5% of total sales to just 3 plantation crops
mainly in developing countries (Gochez 2009).
Other major crop uses are for maize, orchards,
soybeans, vegetables, potatoes, rice, and cotton.
It is used for wheat, apples, oranges, coffee,
cocoa, and rubber. It is used as a pre-harvest
defoliant or desicant on crops such as cereals,
cotton, beans, hops, sugar cane, pineapple, soy,
potatoes, and sunfl owers; and as a post-harvest
desiccant to speed up removal of spent plants
such as tomato plants. It is applied to pine trees
to induce turpentine production. Paraquat is
employed in no-till agriculture, killing grasses and
weeds to minimise ploughing and help prevent
soil erosion. It is used for weed control in nonagricultural
areas such as roadsides, airports,
around commercial buildings, drains, irrigation
ditches, and waterways. It has been employed
for killing illegal marijuana crops in the U.S. and
in Mexico. It has also been reported as used in
shrimp and prawn farming (PAN UK 2003).
Most use takes place in developing countries,
where the conditions of use (hot often humid
climate, lack of protective clothing, leaking
equipment, continuous use, lack of control over
the workplace, lack of awareness of hazard, and
lack of medical facilities) make its use particularly
hazardous.
Paraquat is now being promoted as an
alternative to glyphosate to overcome the
increasing problem of glyphosate resistance in
countries with widespread use of Roundup on
GM crops (Paraquat Information Centre 2010b).
In the US paraquat is recommended for use in
conservation tillage programmes, mixed with up
to 3 other herbicides, each with a different mode
of action, because of the advent of superweeds
like Palmer amaranth (Ho 2010).
Paraquat is also put to a number of illegal uses.
It is believed to have been used to catch mud
lobsters in Fiji, which were linked to the death
of a woman who consumed some (Fiji Times
2010a).
1.6 Manufacturers
Syngenta (formerly Zeneca, ICI), the world‘s
largest agrichemical corporation, is the major
manufacturer (with plants in UK and China),
selling the product under the trade name
Gramoxone. It is produced in many other
countries under different trade names.
China is reported to be the world’s largest
manufacturer of paraquat, and production is
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