Microplastics are solid plastic particles smaller than 5 mm. Significant in this context are persistent plastics such as
- polyethylene (PE)
- polypropylene (PP)
They become an ever-growing problem in lakes, seas and oceans as they find their way into the food chain via microorganisms, fish and birds and finally cause disorders.
PE and PP abrasive bodies in tooth pastes and peeling products are examples for microplastics in hygiene and cosmetic articles. Solid plastic particles that end up in the environment are relatively persistent to UV radiation, atmospheric oxygen, temperature, mechanical influence and microorganisms due to their comparably small surface. Like a microfiber cloth they can adsorb organic substances and frequently pollutants such as petroleum compounds and lipophilic pesticides on their surface.
Plastics in general and microplastics in particular consist of so-called polymers, which form by chaining and crosslinking (cross polymers) of the very same base substance (monomer). The polymers PE and PP are synthetically produced from the monomers ethylene and propylene. Copolymers consist of polymers of a number of different monomers.
There are not only synthetic polymers but also naturally formed polymers such as starch, cellulose, lignin and resins (amber!). Wood, generally known as very resistant, analogously consists of natural copolymers and that is the reason why it is slowly degraded. Peat deposits are an example for natural repositories.
Besides the solid insoluble polymers (plastics) there are water-soluble polymers which are used in the food, cosmetics and pharmaceutical industry. Some examples are
They are used as consistency agents (thickeners), open-pored filming agents, cosmetic (hyaluronic acid) and pharmaceutical active agents (macrogols).
- xanthan gum
- hyaluronic acid
- carbomers (polyacrylates)
- polyethylene glycols (PEG, macrogols)
- carboxymethylcellulose (CMC)
These polymers, by nature, also take more time to degrade than the underlying monomers. Due to their particular form - dissolved in water, hydrophilic - they are completely different from solid lipophilic microplastics. This is the reason why they are faster degraded than solid microplastics by microorganisms and other influences and why they do not adsorb pollutants.
Whereas the discussion around solid microplastics is justified, water-soluble polymers have to be viewed differently.
Dr. Hans Lautenschläger