Cadusafos (2- utan-2-ylsulfanyl(ethoxy)phosphorylulfanylbutane) is a chemical

insecticide Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, i ...

and

nematicide A nematicide is a type of chemical pesticide used to kill plant- parasitic nematodes. Nematicides have tended to be broad-spectrum toxicants possessing high volatility or other properties promoting migration through the soil. Aldicarb (Temik), a ...

often used against

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

nematode populations. The compound acts as a

acetylcholinesterase inhibitor Acetylcholinesterase inhibitors (AChEIs) also often called cholinesterase inhibitors, inhibit the enzyme acetylcholinesterase from breaking down the neurotransmitter acetylcholine into choline and acetate, thereby increasing both the level an ...

. It belongs the chemical class of synthetic organic

thiophosphate Thiophosphates (or phosphorothioates, PS) are chemical compounds and anions with the general chemical formula (''x'' = 0, 1, 2, or 3) and related derivatives where organic groups are attached to one or more O or S. Thiophosphates feature tetrahedr ...

s and it is a volatile and persistent clear liquid. It is used on food crops such as tomatoes, bananas and chickpeas. It is currently not approved by the

European Commission The European Commission (EC) is the primary Executive (government), executive arm of the European Union (EU). It operates as a cabinet government, with a number of European Commissioner, members of the Commission (directorial system, informall ...

for use in the EU. Exposure can occur through

inhalation Inhalation (or inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms, inge ...

or contact with the skin. The compound is highly toxic to

nematodes The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (he ...

earthworms An earthworm is a soil-dwelling terrestrial animal, terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (biology), class (or subclass (biology), subclass, depending on ...

and birds but poses no

carcinogenic A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and Biological agent, biologic agent ...

risk to humans.

History

patent application A patent application is a request pending at a patent office for the grant of a patent for an invention described in the patent specification and a set of one or more claim (patent), claims stated in a formal document, including necessary officia ...

for Cadusafos was first filed in Europe on August 13, 1982 by

FMC Corporation FMC Corporation is an American chemical manufacturing company headquartered in Philadelphia, Pennsylvania, which originated as an insecticide producer in 1883 and later diversified into other industries. In 1941 at the beginning of US involvemen ...

, an American chemical company which originated as an insecticide producer. In their patent application, they claimed that the compound should preferably be used to “control nematodes and soil insects, but may also control some insects which feed on the above ground portions of the plant.” The patent is expired, meaning that the compound is commercially available from chemical vendors such as

Sigma Aldrich Sigma-Aldrich (formally MilliporeSigma) is an American chemical, life science, and biotechnology company owned by the multinational chemical conglomerate Merck Group. Sigma-Aldrich was created in 1975 by the merger of Sigma Chemical Company and ...

. However, the pesticide is not approved for use in Europe due to the lack of information on consumer exposure and the risk to groundwater.

Structure and reactivity

Cadusafos is a synthetic organic

compound which is observed as a volatile and persistent clear liquid. The toxin is an

organothiophosphate Organothiophosphates or organophosphorothioates are a subclass of organophosphorus compounds and of thiophosphate compounds. They are the organic compounds that contain a phosphate group in which one or more oxygen atoms is substituted by sulfur. ...

. Organothiophosphorus compounds are identified as compounds which contain carbonphosphorus bonds where the

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

atom is also bound to

sulphur Sulfur (American spelling and the preferred IUPAC name) or sulphur (English in the Commonwealth of Nations, Commonwealth spelling) is a chemical element; it has Symbol (chemistry), symbol S and atomic number 16. It is abundance of the chemical ...

. Many of these compounds serve as insecticides and cholinergic agents. Cadusafos contains the phosphorus atom bound to two sulphurs which are attached to iso-butyl substituents. The phosphorus is also connected to oxygen by a double bond and is bound to an ethyl

ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R� ...

group. The exact reactivity of Cadusafos as well as that of organothiophosphate compounds in general is, as of yet, unknown. However, the

cholinesterase The enzyme cholinesterase (EC 3.1.1.8, choline esterase; systematic name acylcholine acylhydrolase) catalyses the hydrolysis of choline-based esters: : an acylcholine + H2O = choline + a carboxylate Several of these serve as neurotransmitte ...

enzyme inhibition mechanism of action of these compounds works similarly to other organophosphates. Examples of organophosphates include

nerve gas Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...

ses such as

sarin Sarin (NATO designation GB nerve_agent#G-series.html" ;"title="hort for nerve agent#G-series">G-series, "B" is an extremely toxic organophosphorus compound.VX as well as pesticides like

malathion Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion. The compound's name is presumably ...

Synthesis

The synthesis of Cadusafos can be performed via the

substitution reaction A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...

of ''O''-ethyl phosphoric dichloride and two equivalents of 2-butanethiol.

Mechanism of action

Cadusafos is an

inhibitor Inhibitor or inhibition may refer to: Biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotransmi ...

of the enzyme

acetylcholinesterase Acetylcholinesterase (HUGO Gene Nomenclature Committee, HGNC symbol ACHE; EC 3.1.1.7; systematic name acetylcholine acetylhydrolase), also known as AChE, AChase or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme th ...

. This enzyme binds to acetylcholine and cleaves it into

choline Choline is a cation with the chemical formula . Choline forms various Salt (chemistry), salts, such as choline chloride and choline bitartrate. An essential nutrient for animals, it is a structural component of phospholipids and cell membrane ...

and

acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...

. Acetylcholine is a

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

which is used in neurons to pass on a neural stimulus. Cadusafos inhibits the function of acetylcholinesterase by occupying the

active site In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate, the ''binding s ...

of the enzyme which will no longer be able to function properly, resulting in the accumulation of acetylcholine. This might result in excessive nervous stimulation,

respiratory failure Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a r ...

and death. Cadusafos is an organothiophosphate, which is a subclass of

organophosphates In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...

. Organophosphates can act as an inhibitor for acetylcholinesterase in a way for which the mechanism is known. The active site of acetylcholinesterase contains an

anionic An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

site and an esteratic site. This esteratic side contains a

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − ...

at the 200th position, which usually binds acetylcholine. Organophosphate inhibitors can

phosphorylate In biochemistry, phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols: : This equation can be writt ...

this serine and with that inhibit the enzyme.

Metabolism and biotransformation

In a study, 14C radiolabeled Cadusafos was administered orally to rats. The excretion of feces, urine and CO₂ was monitored for seven days. This showed that cadusafos is readily absorbed (90-100%) and mainly eliminated via urine (around 75%), followed by elimination via expired air (10-15%) and via feces (5-15%). Over 90% of the administered dose was eliminated within 48 hours after administration. Analysis of tissue and blood samples collected after seven days showed a remaining radioactivity between 1-3%. The majority of this radioactivity was found in fat, liver, kidney and lung tissue and no evidence of accumulation was found. A different study was performed in order to identify the

metabolites In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

formed in rats after receiving either an oral or

intravenous Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutr ...

dose of Cadusafos. The metabolic products were analyzed using several analysis methods (

HPLC High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can origina ...

TLC TLC may refer to: Arts and entertainment Television * ''TLC'' (TV series), a 2002 British situational comedy television series that aired on BBC2 * TLC (TV network), formerly the Learning Channel, an American cable TV network ** TLC (Asia), an A ...

, GC-MS, ¹H-NMR and liquid scintillation). This indicated the presence of the parent compound, Cadusafos, as well as 10 other metabolites. The main pathway of metabolism involves the cleavage of the thio-(sec-butyl) group, forming two primary products: Sec-butyl mercaptan and Oethyl-S-(2-butyl) phosphorothioic acid (OSPA). These intermediate compounds are then degraded further into several metabolites. The major metabolites were hydroxysulfones, followed by phosphorothionic acids and

sulfonic acids In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

, which then form conjugates.

Toxicity

A study has been conducted by the Joint

FAO The Food and Agriculture Organization of the United Nations; . (FAO) is a List of specialized agencies of the United Nations, specialized agency of the United Nations that leads international efforts to defeat hunger and improve nutrition ...

WHO The World Health Organization (WHO) is a specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Geneva, Switzerland, and has 6 regional offices and 15 ...

Meeting on Pesticide Residues (JMPR), on rats in which the

lethal dose In toxicology, the lethal dose (LD) is an indication of the lethal toxicity of a given substance or type of radiation. Because resistance varies from one individual to another, the "lethal dose" represents a dose (usually recorded as dose per kilog ...

of Cadusafos was investigated. The researchers found a median lethal dose via the oral pathway of 68.4 mg/kg bodyweight (bw) in male rats and 82.1 mg/kg bw in female rats. The rats died of typical symptoms of acetylcholinesterase inhibition. Via the

dermal The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...

pathway, lower median lethal doses were found; mg/kg bw in males and 41.8 mg/kg bw in females. Considering the toxicity in humans, there is no data available yet regarding the median lethal dose for a human. The

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

(EPA), did publish a report on the safety concerns of Cadusafos used as a pesticide on bananas and concluded that “Potential acute and chronic dietary exposures from eating bananas treated with Cadusafos are below the level of concern for the entire U.S. population, including infants and children.”

Effects on animals

Cadusafos has been proved to be toxic to fish, aquatic invertebrates, bees,

and other

arthropods Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

. Further research was conducted on terrestrial vertebrates, and it is expected to have toxic effects on mammals. Besides its direct toxicity to multiple species, Cadusafos also has a potential to

bioaccumulate Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. Th ...

secondary poisoning Secondary poisoning, or relay toxicity, is the poisoning that results when one organism comes into contact with or ingests another organism that has poison in its system. It typically occurs when a predator eats an animal, such as a mouse, rat, or ...

for earthworm eating mammals and birds should also be taken into consideration. The estimated risk to bees and aquatic organisms is low due to the application of Cadusafos, even though the toxicity to bees is high. The compound is also estimated to be highly toxic to earthworms and birds. A multigeneration study in rats has established a No Adverse Effect Level (

NOAEL The no-observed-adverse-effect level (NOAEL) denotes the level of exposure of an organism, found by experiment or observation, at which there is no biologically or statistically significant increase in the frequency or severity of any adverse effe ...

) of 0.03 mg/kg bw per day for the inhibition of cholinesterase activity in plasma and

erythrocytes Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

. There has been no adequate evidence that Cadusafos could prove a

genotoxic Genotoxicity is the property of chemical agents that damage the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with mutagenicity, all mutagens are genotoxic, but some genotoxic s ...

compound. Due to this and additional research on mice and rats which proved Cadusafos as non-

, it can be concluded that Cadusafos is non-carcinogenic for humans.

Efficacy

Cadusafos proved to be very effective against parasitic

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

populations such as '' Rotylenchulus reniformis'' and ''

Meloidogyne incognita ''Meloidogyne incognita'' (root-knot nematode, RKN), also known as the southern root-nematode or cotton root-knot nematode is a plant-parasitic roundworm in the family Heteroderidae. This nematode is one of the four most common species worldwid ...

''. It showed to be more effective against endoparasitic nematodes than

ectoparasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

nematodes and when compared to other nematicides like triazophos,

methyl bromide Bromomethane, commonly known as methyl bromide, is an organobromine compound with chemical formula, formula Carbon, CHydrogen, H3Bromine, Br. This colorless, odorless, nonflammable gas is Bromine cycle, produced both industrially and biologically ...

aldicarb Aldicarb is a carbamate insecticide which is the active substance in the pesticide Temik. It is effective against thrips, aphids, spider mites, lygus, fleahoppers, and leafminers, but is primarily used as a nematicide. Aldicarb is a cholinest ...

carbofuran Carbofuran is a carbamate insecticide, banned in the US, the EU and Canada but still widely used in South America, Australia and Asia. It is a systemic insecticide, which means that the plant absorbs it through the roots, and from there the pla ...

and phorate, Cadusafos proved to be the most efficient. The effectiveness of Cadusafos improves when increasing the dosage or the exposure time.

Efficacy Efficacy is the ability to perform a task to a satisfactory or expected degree. The word comes from the same roots as '' effectiveness'', and it has often been used synonymously, although in pharmacology a distinction is now often made betwee ...

after application for several successive cropping seasons seemed to remain the same for up to four seasons. However, when it is used for more than 4 consecutive seasons, this can cause a linear decrease in the efficacy.

References

{{reflist Nematicides Ethyl esters Phosphorodithioates Insecticides Thioesters Sec-Butyl compounds