Phosmet

Key takeaways

Phosmet belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Phosmet to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Phosmet from memory before moving on to harder problems.

Reference excerpt

Phosmet is a phthalimide-derived, non-systemic, organophosphate insecticide used on plants and animals. It is mainly used on apple trees for control of codling moth, though it is also used on a wide range of fruit crops, ornamentals, and vines for the control of aphids, suckers, mites, and fruit flies.

History The first registered use of phosmet was in the United States in 1966, where it was used on a variety of crops including fruit trees (apple, pear, peach) and nut trees (almonds, walnuts) as a treatment for various pests such as the codling moth, leafrollers, and others. It has also been registered for use on cattle, swine, and dogs for treatment of lice, fleas, and ticks. It can also be used domestically for trees, bushes, and shrubs by homeowners. Phosmet is being used all over the world.

Structure and reactivity Phosmet is an organophosphate, consisting of a phthalimide and a dithiophosphate ester, with two methyl groups. The structure is a benzene ring connected to an imide, which is connected to the dithiophosphate.

Synthesis Phosmet is produced by reaction of N-chloromethylphthalimide with dimethyldithiophosphoric acid. The former, in turn, can be prepared by the reaction of phthalimide with formaldehyde and hydrogen chloride. Phosmet can also be obtained through the condensation of phthalimide with formaldehyde and conversion of the product to chloride which is reacted with sodium dimethylphosphorodithioate.

Mechanisms of action As an organophosphate, phosmet competitively inhibits pseudocholinesterase and acetylcholinesterase (AChE), preventing hydrolysis and inactivation of acetylcholine. Its inhibitory effects on the AChE enzyme leads to a pathological excess of acetylcholine in the body. Acetylcholine accumulates at nerve junctions, causing malfunction of the sympathetic, parasympathetic, and peripheral nervous systems and some of the central nervous system. Clinical signs of cholinergic excess can develop. The mechanism of inhibition consists of phosmet blocking the active site of the enzyme that binds the ester portion of acetylcholine. If signs of cholinesterase inhibition are present, atropine and pralidoxime are antidotal and may be coadministered.

Biotransformation

Absorption The absorption of phosmet in the body is rapid, based on live rat studies, with almost complete absorption (84.4%) within 24 hours of administering dose. At 0.5 hours after dosing, it was observed that the peak concentration of blood and plasma concentrations are observed. The elimination of phosmet takes place in two phases. The first phase corresponds with the distribution of the compound to tissues and has an observed half life of 0.2 to 6 hours. The second phase corresponds with the direct elimination of the compound and has a significantly longer half life of 41 to 1543 hours.

Distribution The distribution of the compound can be observed and analyzed at every dosage in a variety of tissues. The areas that display the highest level of activity can be found in the liver and the whole blood as this is where the major metabolic process takes place. The lowest level of activity for the compound can be observed in the bone and fat of the individual.

Excretion The primary excretory pathway for phosmet is through the urine or feces, with greater than 70% of the compound being excreted through the former and about 4.5% to 9.9% being excreted in the latter; by 12 hours, more than 50% of the radioactivity can be seen to have been eliminated from an animal organism. There also seems to be a relationship between the dose given to an organism and the excretion of the compound as well the radioactivity; in live animal studies it is observed that at a higher dose, excretion of the compound is significantly slower than at lower doses. Inversely, there is a higher reported radioactivity with acute exposure rather than repeated exposure.

Metabolism In the metabolism of phosmet, there are two major metabolites that are produced and excreted in the urine, N-(methylsulfinylmethyl)-phthalamic acid (U3) and N-methylsulfonylmethyl)-phthalamic acid (U6). The compound undergoes a series of various chemical reactions include thiophosphoryl hydrolysis, S-methylation, hydrolysis of the phtalamide ring to the respective phtalamide acid. The process ends with the sulfoxidation, via an FAD-containing monooxygenase, of the sulfur into either sulfoxide (U3) or sulfone (U6). In addition, analysis of both rat and cockroach faeces and urine in live animal studies showed that phosmet is metabolized in the liver, oxidizing the compound into phosmet-oxon. This is further validated through an in vitro study using rat liver microsomes, for which C-phosmet is incubated with said microsomes, and confirming metabolization of compound. The resulting compound to the metabolism along with U3 and U6 metabolites, is the Phosmet oxygen analogue Phosmet-oxon.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Phosmet

Start with the simplest possible case. Write down what Phosmet claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Phosmet before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Phosmet ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Phosmet

In research: Phosmet appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Phosmet in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Phosmet is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acetylcholinesterase inhibitors, Methyl esters, Neurotoxins, so understanding it makes those chapters shorter.
In everyday life: Look for Phosmet outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Phosmet in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phosmet means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Phosmet out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phosmet in simple terms?

Phosmet is a phthalimide-derived, non-systemic, organophosphate insecticide used on plants and animals. It is mainly used on apple trees for control of codling moth, though it is also used on a wide range of fruit crops, ornamentals, and vines for the control of aphids, suckers, mites, and fruit fl…

Why does Phosmet matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Phosmet?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Phosmet.