Bee Killing Chemicals?

This morning I read a story in the Sydney Morning Herald, "Bunnings to pull pesticide allegedly linked to bee deaths".  According to the story, cans of Yates "Confidor" which have been stocked by the homewares and hardware giant Bunnings, contains neonicotinoid, a class of compounds used as an insecticide that some studies have suggested affects bee's navigation and immune systems and ultimately leads to the death of the bee colony. Indeed, a story on this appeared in New Scientist in July 2017 in which Dave Goulson at the University of Sussex, UK, is quoted as saying, "Although the field trial results varied between countries, the overall evidence points to harmful effects for bees. I think you’d have to be pretty unreasonable at this point not to accept that, at least some of the time, these chemicals harm bees when used in normal farming practice.”  The same story quoted Richard Schmuck of Bayer, one of the makers of this class of insecticides, as saying, "We remain confident that neonicotinoids are safe when used and applied responsibly."

As the name neonicotinoids suggests, these are "new" molecules based on the molecular structure of nicotine shown below:

 Nicotine has been used as a pesticide for over 200 years. It is found lots of plants.  Up to 3% of the mass of the tobacco plant is nicotine, and trace amounts of nicotine are found in vegetables like eggplants, potatoes and tomatoes. When used as a pesticide,  it degrades rapidly in the environment and is not very selective so it is not really a good pesticide. For instance, a dose of 1mg per kg of body mas can kill a human.
Development of neonicotinoids began in the 1980s by Shell and1990s by Bayer. Neonicotinoids are generally less toxic to birds and mammals than they are to insects, and, some of the breakdown products are also toxic to insects, this is why they can be used as insecticides.
Consider the structural formula of imidacloprid, an example of a neonicotinoid and one of the most widely used insecticides:

 Imidacloprid was patented by Bayer in 1985 as the first commercial neonicotinoid. Traditionally insecticides were coated onto plants, "crop dusting", but neonicotinoids like  imidacloprid are water soluble and break down slowly in the environment so they are absorbed by plants. Bees are exposed to these compounds in the plant's pollen.
The early 2000s saw the introduction of two other neonicotinoid compounds;  clothianidin and thiamethoxam. 

clothianidin	thiamethoxam

Clothianidin can be used as a spray, dust or injectable liquid, depending on which plants it is being to protect.
In 2013 the European Union restricted the use of imidacloprid, clothianidin and thiamethoxam on crops that attract bees.

References:
http://www.smh.com.au/national/bunnings-to-pull-pesticide-allegedly-linked-to-bee-deaths-20180113-h0htzq.html
https://www.newscientist.com/article/2139197-strongest-evidence-yet-that-neonicotinoids-are-killing-bees/

Suggested Further Reading
IUPAC Nomenclature:  http://www.ausetute.com.au/namctut1.html
Introduction to Functional Groups: http://www.ausetute.com.au/fungroup.html
Molecular Formula: http://www.ausetute.com.au/molecularformula.html
2-Dimensional Structural Formula: http://www.ausetute.com.au/structural2D.html
Skeletal Structural Formula: http://www.ausetute.com.au/skeletal.html
 Introduction to Polarity of Molecules: http://www.ausetute.com.au/molpolar.html
Intermolecular Forces and Solubility:  http://www.ausetute.com.au/intermof.html
Aqueous Solutions (water as a solvent): http://www.ausetute.com.au/aqueous.html

Suggested Study Questions:

1. Use molecular model kits to build models of  the following molecules:
   • nicotine
   • imidacloprid
   • clothianidin
   • thiamethoxam
2. Draw a 2-dimensional (full display) structural formula for each of the following molecules:
   • nicotine
   • imidacloprid
   • clothianidin
   • thiamethoxam
3. Write the molecular formula for each of the following molecules:
   • nicotine
   • imidacloprid
   • clothianidin
   • thiamethoxam
4. Consider the nicotine molecule. Do you expect it to be soluble in water? Explain your answer.
5. Consider a molecule of imidacloprid. Do you expect it to be soluble in water? Explain your answer.
6. What property of clothianidin enables it to be used as a spray? Explain this property in chemical terms.
7.  What alteration to the structure of a nicotine molecule could you make so that it would become more soluble in water?
8. Carefully compare the structure of clothianidin and thiamethoxam (the molecular models you built could be useful here). In what ways are the molecules:
   • similar
   • different
9. Considering only the structure of nicotine and the neonicotinoids in this article, explain why nicotine might be more toxic to humans than the neonicotinoids.
10. Compare the quotes from Dave Goulson and Richard Schmuck in the article. In what ways are the two quotes:
    • similar
    • different
11. Imagine you have been asked by your government to decide whether or not to ban the use of neonicotinoids in agriculture. What would you advise? Explain why.

AlP Rat Poison

Dozens of mysterious sealed silver canisters containing aluminium phosphide have washed up on Australian beaches between 2012 and 2015. The Australian Maritime Safety Authority (AMSA) suspects all the canisters have come from the same ship which dumped or lost its cargo in the Pacific Ocean. Aluminium phosphide is used as a fumigant to poison rats on ships.

When solid aluminium phosphide, AlP, is exposed to water, it releases highly toxic phosphine gas, PH₃, which smells like rotting fish. The chemical reaction can be represented by the balanced chemical equation shown below:
AlP_(s) + 3H₂O_(l) → PH_3(g) + Al(OH)_3(aq)

This is a proton-transfer reaction in which water is acting as Brønsted-Lowry acid by donating a proton to phosphorus. Phosphorus is therefore acting as a Brønsted-Lowry base by accepting a proton from water. Aluminium phosphide will react with acids according to the following chemical
AlP_(s) + 3H⁺_(aq) → PH_3(g) + Al³⁺_(aq)

These reactions make aluminium phosphide a good choice for ridding a ship of rats.
Firstly, as a solid, AlP can easily be stored as pellets in air-tight, water-tight, containers until it is ready to be used. When required, the pellets can be scattered in the effected area . In the humid air aboard ship, the AlP will start reacting to produce toxic phosphine gas, that is, the area will be fumigated. But it is also possible to entice rats to eat AlP pellets mixed with food, in which case it will act as pesticide, because on entering the acidic stomach of the rat, it will produce the toxic phosphine.

Aluminium phosphide is  a very effective way to get ride of rats, so much so, that is widely used in agriculture to remove rats from grain silos.

References:
"Toxic canisters washing up on Australian beaches pose serious health risk"
 http://www.smh.com.au/environment/toxic-canisters-washing-up-on-australian-beaches-pose-serious-health-risk-20150917-gjp5se.html

"Controlling rabbits with aluminium phosphide tablets"
 http://agriculture.vic.gov.au/agriculture/farm-management/chemical-use/publications/chemical-industry-news/chemical-industry-news-no.-75-summer-autumn-2013

"Phosphine fumigation"
https://www.worksafe.qld.gov.au/injury-prevention-safety/hazardous-chemicals/specific-hazardous-chemicals/phosphine-fumigation

Further Reading
Definition of Acids and Bases
Proton-transfer Reactions
Mass-mole Calculations
Molar Volume of Gases

Suggested Study Questions:

1. The symbols of some elements are listed below. Name each element.
   • Al
   • P
   • H
   • O
   • K
   • He
   • At
2. Calculate the amount of aluminium phosphide in moles given the masses of AlP given below:
   • 10 g
   • 10 kg
   • 10 mg
   • 10 μg
3. Calculate the moles of phosphine gas produced when each mass of AlP below reacts with excess water in a ship's hull:
   • 10 g
   • 10 kg
   • 10 mg
   • 10 μg
4. Based on your answers to question 3 above, calculate the mass of phosphine produced for each mass of AlP used.
5. Your ship is sailing towards eastern Australia and has just crossed the Tropic of Capricorn. You have been asked to estimate the volume of phosphine gas that will be produced when you release AlP pellets into the ships hold. Which molar gas volume will you use; 22.71 L or 24.79 L ? Explain your answer.
6. Rats are currently infesting a small part of your ship, about 150 m³. How much solid AlP would be required to fumigate this area, but not leave any AlP residue left over?
7. The Cook has already tried to fumigate the pantry and is sure there is a silver canister around that still contains some AlP, it could be in the pile of empty canisters, or, it could be in the pile of full canisters. No-one wants to kill themselves by opening the canisters to find out, so can you suggest a method that could be used on board ship to determine how much AlP is present in each canister.
8. Explain why the reaction between aluminium phosphide and water is described as a proton-transfer reaction and not as a redox reaction.
9. Explain why, even though aluminium phosphide and phosphine are toxic, it is considered safe to use these to fumigate silos containing grain which will be eaten by humans.
10. The silver canisters that have washed up on Australian beaches have no labels, presumably these have come off while they were in the ocean. You have been asked to design new labels for the canisters. The labels must include suitable safety and handling information.