This happens everywhere and to this day and to this current moment happening right now even on a molecular scale. Happening on a scale we cannot see visibly. But, we can feel it and experience its consequences.
This is what we call migration and this is what are discussing today but not on a huge macro-scale, we are referring to the small minute stuff where the fun exists
- Definition
- Why do we say food matrix?
Food itself is a complex system consisting of various compounds existing altogether which gives it its physical, chemical, and organoleptic characteristics.
- How does this phenomenon happen?
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| https://byjus.com/biology/diffusion/ |
Food contact materials (FCMs)
Materials that come into contact with foods whether solid or liquid to contain/store/uptake/hold and to process them.
We have so many examples of these materials such as ceramics, rubber-based, plastic-based, aluminum, wooden, stainless steel, glass, and silicon-based
Observe the following pictures with the logo drawn on the label for the products
Now we get to the 3 big questions we need to ask ourselves and answer them through the lecture
- What makes a good candidate for food packaging?
- Origin of pollutants
- How does a pollutant migrate to the food matrix?
What do you think?
· To begin with, it must be able to protect the food from the outside environment obviously
· Cost effective (why would I invest in something that's proven to be extremely expensive?)
· It shouldn't break easily or else I would be losing (Economical and reputational value)
· It can be recycled to some extent
· Have a long shelf-life (high durability)
· Easily handled, transported, and processed
All of these good properties are required when we are looking for a good candidate to protect our foods after all, we are doing this to ensure one major rule which is to provide safe and sound food.
Finding a material that checks all these properties is like finding the hero of packaging materials and of course, major production companies will definitely capitalize on that and produce an ocean size amount of it
Let's take one food contact material and dissect it to the smallest scale. PLASTIC! I think without a doubt we could say that over 90% of us have used or are right now in possession of a plastic-based food contact material.
Plastic has most of the properties we mentioned earlier so why not produce tons of it
It is as if we have found the perfect material, NO!, wrong!!! let's agree that nothing is perfect!
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| Image source https://www.tradeindia.com/products/light-weight-smooth-finish-1-liter-plastic-bottle-8013853.html |
Perfection makes a dead end, grayish life with no joy, once reached (if possible) then you have got nothing else to do.
So now that we have discovered one of the globally produced materials of all time, we are now bearing its consequences. These are the challenges we are facing right now, handling the material, its raw materials (resources) which is a finite aspect, and shifting to sustain the resources. Last but not least, disposing of it or the correct disposition process.
All that we are referring to right now are the contaminants, they are countless. Such contaminants can migrate from food packaging materials. We will be discussing one contaminant with all its aspects. And perhaps the famous one that can exist everywhere is "Lead"
Now that we have defined what a good candidate for food packaging materials is, we shift to the second question which is " the origin of pollutants/contaminants"
Let's look at where can Lead originate from
An everyday source we may not realize is traffic, a study was made on Forty-five traffic controllers of Alexandria, Egypt road intersections on the assessment of lead toxicity, and found out that the average blood lead level was 68.28 ug/dl while according to the Council of State and Territorial epidemiologists reference blood lead level value is 3.5 ug/dl - this revelation clarified the reasons behind some traffic controllers sudden death when they arrive home falling down on the ground breathless.
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| Image source - https://www.uags.com.au/symbolic-traffic-controller-600-x-600-corflute |
Think about it for a second, you have people with god knows health conditions, their own workspace exists in a place where they are constantly experiencing non-stop origin of lead which is owed to the presence of something that is being the main reason for air pollution by lead.
This is because some gasoline use still has lead in it, (The use of leaded-gasoline) although some countries banned its use, some still use it. As well as, the products resulting from the lead-acid car battery.
Blood lead levels exceeding 25 ug/dl require immediate removal of the worker from the area to which blood lead levels increase
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| Image source - https://e360.yale.edu/features/tire-pollution-toxic-chemicals |
Now we move on to a second origin for lead which is the plastic material itself and its additives. From here on we are digging deeper into the real stuff.
We need first to know
how plastic is made/built. Think about it like how any building is built, you
need bricks as the building units (main) you need something to connect
each brick to one another (cement), you are going to need some supporting
materials (things to provide overall strength) like iron bars and for extra rigidity,
we will need sand and stones as fillers for any gaps and base reinforcement.
Let's put things into comparison, the bricks
are the main units - the things that make up the buildings, the
walls.
Same thing with plastic,
imagine the plastic is the main building unit and I am using something
equivalent to the bricks but on a smaller scale, we have main building units we
call them monomers, and the connecting substance here is the bond
that is making them attached to each other, and some added fillers and
strength and rigidity providing additives to make the bottle withstand
environmental factors e.g., UV light, oxidation, mechanical stress, and heat.
Monomers are like the bricks we discussed minutes ago when building, they are the soldiers, and they are the ones with the highest number in the system. Observe the following figure, a plastic bottle -these red dots are the monomers, they are the bricks we are talking about, these are millions upon billions of molecules bonded up together making up this shape we see right now.
Imagine it as if you see a pile of dust piled up together in a corner, if you just blow in it enough, this pile of dust will disperse into the air, and you will be able to see the particles of dust while they are still a little somewhat close to each other but then suddenly it is out of sight. Can you even see one particle? Of course not! so we can depict that the piled-up dust is a complete entity with atoms, these atoms are the dust particulates when they were piled up they were enough that we can see them.
The same applies to
anything we see right now including us, we are piles upon piles of atoms connected
to each other in a certain way in an unimaginable sophistication which ended up
making the glorious wonder of you. You deserve to be appreciated. Keep going!
Besides that, we have ingredients that assist the building blocks with some properties that make it a good candidate for packaging a food commodity, such as:
Fillers, Colorants, Lubricants, Plasticizers, and Antioxidants all of them are joining the main raw materials that make up the plastic material
These materials are like stones, sand, and iron bars they provide rigidity, strength, and ability to withstand environmental factors such as heat, sunlight, humidity, air, and mechanical impacts
Some ingredients provide aesthetic value such as pigments that are used as colorants and make up any art on your everyday cup of coffee
For instance, we have
different types of colorants they can be inorganic, organometallic or metallic compounds such as lead chromate which gives the color yellow, and Lead sulfate and molybdate both give
a red color.
Furthermore, we have
colorants that have cadmium as an ingredient such as Cadmium sulfide and
Cadmium selenide giving yellow and red pigments respectively.
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| Image source - https://pubmed.ncbi.nlm.nih.gov/34030075/ |
Even though metallic-based colorants exist, some countries prohibit their use.
Colorants are another source of lead pollution in food packaging materials.
Now we visit another source of Lead which comes from the early stages of production, let's roll back a little bit to when we spoke about how buildings are built from building blocks/units. We related that to the plastic materials being made up of units that we called Monomers, a Greek word that is divided into two words "Mono" which is equivalent to = one, and "Meros" which is equivalent to = part, putting them together makes up the word "one part" so we have one part connected to another part and so on and so forth till we make up the building or in our case the plastic bottle we use every day.
The following figure is more of a microscopic 2d-diagram of what one particle of our main building units (monomer) looks like, the following circular shapes are molecules with the bonds connecting them.
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| Image source - https://www.sciencedirect.com/topics/earth-and-planetary-sciences/polyethylene-terephthalate |
Polyethylene terephthalate or PET, is your everyday plastic. As a matter of fact, if any of you have a plastic water bottle right now, I would like you to look at the bottom of it, you should find this symbol on it (a picture of PET plastic bottle symbol).
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| Image source - https://www.vectorstock.com/royalty-free-vector/set-of-plastic-recycling-symbols-vector-23551758 |
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| Image source - https://www.alamy.com/polyethylene-terephthalate-or-pet-pete-polyester-thermoplastic-polymer-molecule-with-plastic-bottle-structural-chemical-formula-vector-illustratio-image260834432.html |
And this is another form of what it looks like (a picture of a series of PET molecules attached to each other)
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| Image source - https://www.sciencedirect.com/topics/earth-and-planetary-sciences/polyethylene-terephthalate |
This is a detailed picture of what Polyethylene terephthalate looks like, it consists of two main compounds, an Ethylene group, and a terephthalate group. Now let's get to know how we even obtain these molecules which further elaborate on how Lead can ultimately exist in a matrix of compounds that don't have lead element as a contributing member of its compound structure.
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| Image source - https://byjus.com/chemistry/polyethylene-terephthalate/ |
Crude oil! The beginning of everything, Petroleum. A mixture of compounds that can make anyone rich once they find out that they have been seating before a gold mine! But why is that? well crude oil produces numerous substances that are used in different industrial aspects. Let's take a look, we have a variety of compounds with each one of them produces different products. Our main concern lies in
"Naptha series", Here lies a couple of compounds that make up different products with two of them being the raw materials for PET plastic production which are Ethylene and terephthalic acid.
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| Made by me |
To obtain these compounds, a complex process must be done to the crude oil to extract and separate these compounds from the mixture that makes up the crude oil, this process is called "Fractional distillation" This complex step-by-step process is used to separate the mixture of compounds found in crude oil through heat at which one or more fractions of the mixture will vaporize with the most volatile compounds gets separated at the highest chambers with the lowest boiling points and the solid high boiling point compounds at the bottom to which the highest temperature exist and where usually the heavy metals can be found in abundance. While this process is the most common form of separation technology. Yet, it requires immense accurate implementation to avoid any impurities that can be separated into categories that they aren't supposed to be found in. This is due to the application of the temperature and it needs to be gradually done without the need of conducting it too fast since some of these compounds have close boiling temperatures so you may have impurities in areas that aren't supposed to have them.
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| Image source -https://www.alamy.com/diagram-showing-fractional-distillation-crude-oil-image444606928.html?imageid=4E336B6A-2317-45D0-A1A0-00B3330A2110&p=540308&pn=1&searchId=4e5272b96c5da6732d92752d6afca851&searchtype=0 |
This implies that there is a chance for sure that there is a chance of having heavy metals in any of the different categories of the distillation products and that's why we end up finding heavy metals like lead or cadmium in the raw materials.
As you can see in this table, the concentration of some heavy metals in a sample of crude oil, heavy metals concentrations (in mg/liters) are through the roof.
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| Image source - https://www.researchgate.net/publication/321148024_Alterations_in_the_Bio-membrane_of_Libyodrilus_violaceus_following_Exposure_to_Crude_Oil_and_Its_Fractions/figures?lo=1 |
Now that we have answered the second question, we move on to the third and last question of our topic which is "How does a pollutant migrate to the food matrix?"
No matter what we do, there is always migration. But, we always thrive to make sure it is incredibly in the safest levels and are at levels below the safe daily intake or detection.
LEAD!, It is obvious now that there is no way we could avoid it. It is now existing in our polymer. If we look at our plastic bottle right here and zoom in on a portion of it, this should be how the polymer looks like, the green-arranged alternating line is our polymer consisting of millions upon billions of molecules of polyethylene terephthalate molecules connected to each other side by side with some components attached around like any additives (e.g., plasticizers, antioxidants), as well as colorants (Recall: Lead chromate for instance), and of course, there exist impurities hanging around!.., Hanging like any disease that visit you and hang out with you sometime and leave.
Notice closely how uniform this portion and the arrangement of molecules are, this way of arrangement isn't just for show and tell, it exists and for a reason, it characterizes the molecules forming this arrangement it gives it properties. For instance, with such a pattern, the structure gets to be tough, rigid, and to an extent able to withstand heat.
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| Image source - https://www.sciencedirect.com/science/article/abs/pii/S0278691521004063 |
These types of patterns we call them "Crystalline patterns" You know the word crystal is implied on things and context that appear clear and understood well just like diamonds and how beautiful and clear they are! They are the perfect example to describe crystalline structures, the structures that have a clear uniform, and edged points.
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| Image source - https://www.astteria.com/blog/how-to-identify-a-raw-diamond/ |
This is a comparative diagram showing crystalline structures and their opposite "amorphous structures" and we know how strong diamonds are! they cut things, man! so this implies a lot about how just a pattern of atoms contributes to the physical properties of something.
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| Image source - https://www.geeksforgeeks.org/difference-between-crystalline-and-amorphous-solids/ |
On the other hand, we see amorphous structures and look at how unarranged the molecules are, this tells us a lot about what physical properties we are expecting. Moreover, heat stability as well is also shown to be stronger in crystalline structures than in amorphous types
Some materials can have both phases or structures in it, and we call them "Semi-crystalline" and our PET bottles fall somewhere in this category. It has some regions with molecules arranged, parallel to one another and uniform. On the other hand, some regions are irregular in arrangement.
These types of regions affect the material a lot and make it a good candidate to be easily released when affected by different factors such as heat, pH, contact time, and the existing solvent.
Now, we have seen what is like to be a plastic PET bottle with its building units' structure, here again, we have our building units colored in red and let's say these bright blue small circles are the lead impurities that exist in our plastic complex structure. By cutting off a piece from this bottle and examining it clearly on a smaller scale and zooming extremely close. We can see how something like this bottle behaves on a small scale. Remember that we are now dealing with things that can have diameters on a micro-scale.
We have an intricate matrix of molecules connected to each other with two main regions made up by our polymer, look at the arrangement, parallelism, and uniformity of crystalline regions, and tell me how something like that gets to be bothered easily! This is pure support in its form! molecules standing next to each other and in front of one another to protect and serve in every possible way while in contrast, the amorphous regions and their chaotic arrangement, what do you expect from selfishness!
These parts are usually the ones prone to migration much faster and their properties make them an easy target for temperature, the distribution of heat in this part is more devastating than the regular uniform regions and so the freedom of parts, molecules, or even portions is much much faster and easier in here.
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| Red dots represent monomers - blue neon dots represent lead Image source - https://www.sciencedirect.com/topics/earth-and-planetary-sciences/crystallinity |
To fully understand what temperature could do to anything, we need to look at the basic phases of life (Solid, liquid, and gas phases) they are the three phases of matter.
Solid state matter is expressed when the molecules are extremely close to each other, with strong bonds attached to every molecule intact/very close and once let's say the temperature is applied to it, the integrity of the object begins to stretch and this on a molecular scale is due to the increased kinetic energy resulted from an external source which is heat, energy was gained due to it and so the electrons were excited and this gained kinetic energy resulted in increased mobility of the molecules and so the bonds stretched and the solid state morphology began to disintegrate and change its strong form to liquid state which is expressed as molecules with bonds less close to each other than it was in its solid state.
By continuing to apply heat to the matter, bonds no longer strongly tact anymore and even stretch much longer creating a state where atoms are a part of each other and thus enter the gas phase.
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| Made by me |
When the temperature rises let's say from a hot drink, the heat is distributed everywhere in the system even the contact material, and taking into account many factors such as the history of this plastic starting from how it was manufactured, quality of raw materials and where the additives/substances added to aid the polymer production and give characteristics to the final product, in the right concentrations and according to regulations.
All of these points account for the percentage of migration whether it will be high or low or somewhat in the middle.
The increased heat with no doubt can affect and will make changes to the materials on the molecular scale leading to bond breaking and thus migration!
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| Made by me |
Let's get into the real fuzzy yet amazing stuff. Here we have two atoms colored blue bonded to each other, this line indicates the presence of a bond, this 2D-imaging of how a chemical bond exists, and of course it is hypothetical.
It is more like an attraction force, remember that electrons are negatively charged and the nucleus of any atom is positively charged owing to the presence of protons which are positively charged particles inside the nucleus, and so, the electrons of one atom are attracted to the positively charged nucleus and the same with the opposite atoms' electron. Yet, they will never fully reach the opposite nucleus, Why?
Because of the repulsive force resulting from the negatively charged electrons from both atoms when they are approaching the nucleus of the other, these constant forces balance the bonded molecules together.
Atoms at any given system and state of life whether solid, liquid, or gas are constantly moving in their place. Observe the following figure, shared electrons between covalently bonded atoms are moving one at a time around each atom.
Let's apply temperature! >:)
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| Made by me |
I want you to watch closely the behavior of the electrons, we are gradually increasing temperature, this increases the vibrational motion of the molecules owing to the movement of electrons, they are becoming more and more erratic.
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| Made by me |
This vigorous action going on right now due to the applied temperature at a certain point will be overwhelmed by the increased input of energy (temperature) to a point that it will surpass the force that is keeping the atoms bonded together and then you have it!
You successfully separated a molecule!
Remember, this could be anything, it can be a monomer, a dimer, an additive such as colorants or thermal stabilizers, or it could be Lead!
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| Made by me |
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| Made by me - image source -https://www.sciencedirect.com/topics/earth-and-planetary-sciences/crystallinity |
- Egyptian National Food Safety Authority Food Contact Materials Decree 17/2022
- https://www.efsa.europa.eu/en/efsajournal/pub/5194
- Noorlander, et.al., 2011. Levels of per-fluorinated compounds in food and dietary intake of PFOS and PFOA in the Netherlands. Journal of agricultural and food chemistry
- Migration of Substances from Food Packaging Materials to Foods IOANNIS S. ARVANITOYANNIS &LOULOUDA BOSNEA
- Migrating Levels of Toxic Heavy Metals in Locally Made Food Packaging Containers, Saimah khan, Abdul Rahman Khan
- https://www.news.iastate.edu/news/2015/08/21/vorstplastics
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- Leaching of Lead, Chromium and Copper into Drinks Placed in Plastic Cups at Different Conditions, Oliver Ahimbisibwe et.al.
- https://www.cdc.gov/nceh/lead/prevention/sources/water.htm#:~:text=Lead%20can%20enter%20drinking%20water,acidity%20or%20low%20mineral%20content
- https://www.digicomply.com/restricted-substances/lead-molybdate
- https://www.e-education.psu.edu/fsc432/content/overview-refinery-products-and-processes
- https://www.bpf.co.uk/plastipedia/how-is-plastic-made.aspx
- https://plasticseurope.org/media/plastics-europe-launches-the-plastics-the-fast-facts-2023/
- https://www.e-education.psu.edu/fsc432/content/metals-content-and-total-acid-number#:~:text=Most%20common%20metals%20that%20are,the%20source%20of%20crude%20oil.
- https://alevelchemistry.co.uk/notes/fractional-distillation-of-crude-oil/#Napthalene_series
- https://www.eurekalert.org/multimedia/698438
- Thermomorphological study of the terahertz lattice modes in polyvinylidene fluoride and high-density polyethylene Steffan et. Al
- Microplastic Pollutants, Christopher Blair Crawford & Brian Quinn 2017 Elsevier
- Assessment of Lead Toxicity in Traffic Controllers of Alexandria, Egypt, Road Intersections, Ahmed et. Al
- Physical Metallurgy, Robert W. Cahn and Peter Haasen – Fourth, Revised and Enhanced Edition 1996
- https://www.cdc.gov/niosh/topics/lead/referencebloodlevelsforadults.html#:~:text=The%20Council%20of%20State%20and,value%20is%203.5%20%C2%B5g%2FdL.
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Alterations in the Bio-membrane of Libyodrilus violaceus following Exposure to Crude Oil and Its Fractions
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