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Metaldehyde is an
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...
with the formula (C8H16O4). It is used as a pesticide against slugs,
snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...
s, and other gastropods. It is the cyclic
tetramer A tetramer () ('' tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula ...
of acetaldehyde.


Production and properties

Metaldehyde is flammable, toxic if ingested in large quantities, and irritating to the skin and eyes.  It has a white crystalline appearance with a menthol odor. Metaldehyde is obtained in moderate yields by treatment of acetaldehyde with various acid catalysts, such as
hydrogen bromide Hydrogen bromide is the inorganic compound with the formula . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room tempe ...
, and cooling. The liquid trimer, paraldehyde is also obtained. The reaction is reversible; upon heating to about 80 °C, metaldehyde and paraldehyde revert to acetaldehyde. Metaldehyde exists as a mixture of four
stereoisomers In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms ...
, molecules that differ with respect to the relative orientation of the
methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ma ...
s on the 8-membered ring. The stereoisomers have respectively the molecular symmetries C (with symmetry of order 2), C (order 4), D (order 8), and C (order 8). All have at least one plane of reflexion, so none of them is
chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from i ...
.


Uses


As a pesticide

It is sold under various
trade name A trade name, trading name, or business name, is a pseudonym used by companies that do not operate under their registered company name. The term for this type of alternative name is a "fictitious" business name. Registering the fictitious name w ...
s as a
molluscicide Molluscicides () – also known as snail baits, snail pellets, or slug pellets – are pesticides against molluscs, which are usually used in agriculture or gardening, in order to control gastropod pests specifically slugs and snails which damag ...
, including Antimilice, Ariotox, Blitzem (in Australia), Cekumeta, Deadline, Defender (in Australia), Halizan, Limacide, Limatox, Limeol, Meta, Metason, Mifaslug, Namekil, Slug Fest, and Slugit. Typically it is applied in pellet form, but it is also found as a liquid spray, granules, paste, or dust.  Often the pesticide includes bran or molasses to attract pests, making it attractive to household pets as well. Metaldehyde is effective on pests by contact or ingestion and works by limiting the production of mucus in mollusks making them susceptible to dehydration. Metaldehyde products were used to control the invasive African land snail population in Miami-Dade County in Florida.  Experimental use permits from the U.S. Environmental Protect Agency authorized the application amount and usage in residential areas. Due to the contamination of drinking water by metaldehyde's use in agriculture, a specialist organisation was established in 2008 called "The Metaldehyde Stewardship Group (MSG)". On 19 December 2018, the British government banned the use of metaldehyde slug pellets outdoors from spring 2020; after this date it would only be legal to use it in permanent greenhouses. In July 2019, the ban was overturned after the High Court in London agreed with a challenge to its legality. Metaldehyde pellets returned to the UK market until 18 September 2020, when the British government banned the use of metaldehyde slug pellets outdoors after 31 March 2022.


Other uses

Metaldehyde was originally developed as a solid fuel. It is still used as a camping fuel, also for military purposes, or solid fuel in lamps. It may be purchased in a tablet form to be used in small stoves, and for preheating of Primus type stoves. It is sold under the trade name of "META" by Lonza Group of Switzerland; it can be included in the
field ration A field ration (combat ration, ration pack, or food packet) is a type of prepackaged or canned military ration. Field rations are distinguished from garrison rations by virtue of being designed for minimal preparation in the field, as well ...
of some nations.


Safety and toxicity to pets and humans

Metaldehyde has a toxicity profile identical to that for acetaldehyde, being mildly toxic and a respiratory irritant at the 50 ppm level. In terms of water safety, during periods of rainfall metaldehyde pellets become agitated and can seep into natural water courses. The European Commission restricts metaldehyde levels to 0.1 µg/L in drinking water. Metaldehyde-containing slug baits are banned in some countries as they are toxic to dogs and cats and disturb the natural ecosystems. There is no antidote or specific treatment plan for metaldehyde poisoning. Symptoms of poisoning in dogs and cats vary and are very similar to poisonings by other substances, however they can include tremors, drooling, hyperthermia, vomiting, and restlessness.  If left untreated, symptoms will proceed to seizures and death within days.  Severity of symptoms and speed of onset depend on the quantity ingested and the other contents of the stomach which affect absorption. A diagnosis can be made by an analysis of stomach contents, which tend to have an apple cider vinegar odor, as well as a history of exposure to the chemical.  Treatment includes IV fluids, sedation, lowering body temperature, and purging of stomach contents with charcoal.  Prompt and aggressive medical attention after a poisoning may make a full recovery possible within 2–3 days. Due to this toxicity, pet owners may want to investigate alternatives which are not as toxic to pets, such as
Ferric Sodium EDTA Ferric sodium EDTA, also known as sodium ferric ethylenediaminetetraacetate, is a broad spectrum molluscicide used to kill snails and slugs and protect agricultural crops and garden plants, and in particular to eliminate infestations of '' Cornu as ...
or
iron(III) phosphate Iron(III) phosphate, also ferric phosphate, is the inorganic compound with the formula Fe PO4. Several related materials are known, including four polymorphs of FePO4 and two polymorphs of the dihydrate FePO4·(H2O)2. These materials find few ...
. The metaldehyde tablets resemble candies and do not taste bad, making accidental ingestion possible by children or even by adults unaware of their true nature. Their use was popular during the interwar period and several cases of poisoning resulted. Baits may contain a
bittering agent A bittering agent is a flavoring agent added to a food or beverage to impart a bitter taste, possibly in addition to other effects. While many substances are bitter to a greater or lesser degree, a few substances are used specifically for their bi ...
to prevent accidental consumption by pets or children. Oral ingestion of metaldehyde have been described in adults attempting suicide. Amongst them, majority experienced gastrointestinal or neurological symptoms. When compared to humans with accidental ingestion of metaldehyde, those attempting suicide tended to be symptomatic, develop seizures, require care at the intensive care unit, and suffered longer hospitalizations.


See also

*
Methiocarb Methiocarb is a carbamate pesticide (an acetylecholinesterase inhibitor) which is used as an insecticide, bird repellent, acaricide and molluscicide since the 1960s. Methiocarb has contact and stomach action on mites and neurotoxic effects on m ...
* Paraldehyde


References


External links


National Pesticide Information Center (NPIC)
Information about pesticide-related topics. *
Get Rid of Slugs and Snails, Not Puppy Tails! Case Profile
- National Pesticide Information Center *

- National Pesticide Information Center

* Slug controls (on Wikibooks) * {{PPDB, 446 Molluscicides Acetals Oxygen heterocycles Eight-membered rings Heterocyclic compounds with 1 ring