Microplastics: Health effects

Don Smolenski, Contributing Editor | TLT Machinery October 2022

Toxicity studies show negative outcomes from microplastics exposure, but there is more work to be done to understand the impacts and mitigate the effects.
 
Two of my recent TLT columns dealt with microplastic refuse in water and in air.1,2 This article will do a cursory review on the potential health effects of microplastics and nanoplastics. It’s well documented that microplastics (particles <5 mm in diameter) and nanoplastics (particles <1 μm in diameter) are found in air, water, food, human tissues—virtually everywhere. The question, however, is, how might they be affecting human and animal health?

I previously commented that one of the difficulties of addressing this issue is that the particles are greatly variable in size, shape and composition, and better understanding these factors will be critical in conducting toxicology studies.3 Size can be defined somewhat easily. Shape is considerably more difficult. Spherical particles have been used in some studies, but particles found in the environment typically are sharp-sided, jagged and have pointed edges. A toxicity study in 2008 showed that large fibrous carbon nanotubes elicited a negative response in mice similar to asbestos.4 Another study showed that the shape of the particles affected the interaction with cells.5 Those particles with the most edges showed the greatest toxicity. What is on the surface of the particles also is important, be it there intentionally, or biofilms and metals, endotoxins or other molecules that deposit during aging. Amine groups, for instance, caused a stronger biological response than carboxylates. As far as composition, most polymers, such as polystyrene or polyethylene, contain pigments, plasticizers and sometimes metals. Oxidation and ultraviolet weathering also will affect the ultimate composition of the particles.

Potential exposure from microplastics and nanoplastics would likely come from ingesting the particles with food or inhaling particles present in the air. In vivo studies are just not practical for defining potential health hazards. In vitro studies are being performed to evaluate particle effects in the human gut or lungs. In some in vitro studies, microplastic particles were found to potentially double the bioavailability of fat and reduce micronutrient absorption. These types of studies could be used to focus where in vivo studies could potentially be conducted. Studies at Baylor University were conducted to investigate the effects of different size particles on the effects of intestinal epithelial cell viability and on the viability of three strains of common gut bacteria. The smaller particles decreased the viability of the epithelial cells and decreased the growth of the beneficial bacteria. The larger particles, however, increased the growth of bacteria, perhaps as a food source. There also was some work on potentially respirable particle. Air sampling found high levels of microplastic particles in the air of a gym. The polymers found were consistent with nylon sportswear material.

It’s clear that the better researchers understand how microplastic particles effect cellular systems, the sooner they can begin to create toxicity models. These could be useful in assessing the potential toxicity of new microplastics early on in their development. Very smart and thorough research must be conducted to balance the risks versus benefits of microplastics. There’s a great deal of work yet to be done!

REFERENCES
1. Smolenski, D. (2022), “Microplastics,” TLT, 78 (6), p. 104. Available here.
2. Smolenski, D. (2022), “Microplastics: Still up in the air,” TLT, 78 (8), p. 72. Available here.
3. Erickson, B. E. (May 30, 2022), “Getting a grip on microplastics risks,” Chemical & Engineering News, 100 (19). Available here.
4. Poland, C., Duffin, R., Kinloch, I., et al. (2008), “Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study,” Nature Nanotech, 3, pp. 423-428. Available here.
5. Kocher, C. (Aug. 23, 2021), “How do microplastics affect living cells? Research to focus on irregularly shaped particles,” BingUNews. Available here.
 
Don Smolenski is president of his own consultancy, Strategic Management of Oil, LLC, in St. Clair Shores, Mich. You can reach him at donald.smolenski@gmail.com.