Microplastics measured in humans
In an article published on July 31, 2023, in the journal Science of the Total Environment, Luigi Montano from the Local Health Authority Salerno, Oliveto Citra, Italy, and co-authors analyzed microplastics in human semen and discussed potential mechanisms on how the plastic particles entered the semen.
The scientists collected semen from ten participants aged between 18 and 35 years and living in a polluted area in Southern Italy. Besides counting microplastics by Raman microspectroscopy, they also assessed semen quality (e.g., sperm concentration, mobility, and morphology) according to the World Health Organization (WHO) guidelines.
One to five micro-sized plastic particles (2-6 µm) were detected in six out of the ten samples covering several polymer types. Most microplastics had an irregular shape. Consulting further scientific literature, the authors discussed the mechanisms by which the plastic particles have crossed the “blood-testis barrier.” This barrier prevents blood and immune cells from entering the endoluminal compartment where the spermatogenesis takes place.
Given the particles’ small size from two to six µm, the researchers hypothesized that particles entered the semen “via the epididymis and also from the seminal vesicles, which are the most susceptible to inflammation.” Comparing semen quality and microplastic presence showed that the quality was highest where no particles were detected. However, the scientists emphasized that given their small sample cohort, their results would be preliminary, making further investigations to verify this relationship necessary.
Previous studies detected microplastics in human semen as well as in testis but Montano et al. are the first to associate exposure directly to sperm quality. Mean sperm concentration has been found to decline by 52.4 % between 1973 and 2011 among men from North America, Europe, Australia, and New Zealand. That microplastics can affect male reproductive health has been demonstrated for mice. And in the female reproductive system, including the human placenta, small plastic particles have been detected and shown to affect the offspring.
Human biomonitoring studies have further encountered microplastics in blood in a mean concentration of 1.6 µg/mL. Yunxiao Yang from the Medical University, Beijing, China, and co-authors were interested if microplastics are present in the human heart and its surrounding tissues. In their article published on July 13, 2023, in the journal Environmental Science & Technology, they described findings from 14 cardiac surgery patients. Samples included six pericardia, six epicardial adipose tissues, eleven pericardial adipose tissues, three myocardia, five left atrial appendages, and seven pairs of pre- and postoperative venous blood samples which were all analyzed by Laser direct infrared chemical imaging system and scanning electron microscopy.
Yang and co-authors detected microplastics between 20 and 469 µm in size in all analyzed tissue types but not in all analyzed samples. Most were made up of polyethylene terephthalate (PET) and polyurethane (PU). Opposed to that microplastics were detected in every blood sample but in lower levels. Comparing pre- and post-surgery blood, the researchers reported that microplastic characteristics changed (e.g., becoming smaller after surgery). However, “[t]he presence of poly(methyl methacrylate) in the left atrial appendage, epicardial adipose tissue, and pericardial adipose tissue [was attributable] to accidental exposure during surgery,” the authors discovered and called for further research to investigate the impact of surgery on microplastic introduction.
Microplastics released from plastic containers into baby food
Not only during surgery but also in daily life, microplastics may enter the human body, for instance, if taken up with plastic-packaged foods and beverages. On July 20, 2023, ScienceDaily reported on a study published in Environmental Science & Technology that found baby food containers made of plastics to release billions of plastic particles.
The news provider summarized that individual baby food containers available in US stores may release over two billion plastic particles in the nano-range and four million in the micro-range per square centimeter of the container when microwaved. “Knowing the extent of plastic particle ingestion is crucial in understanding the potential harm they may cause,” said the lead author of the study Kazi Albab Hussain. The team of researchers further exposed embryonic kidney cells to the plastic particles released from the container over several days to mimic the concentrations infants are exposed to. “After two days, just 23% of kidney cells exposed to the highest concentrations had managed to survive — a much higher mortality rate than that observed in earlier studies of micro- and nanoplastic toxicity,” ScienceDaily summarized the findings.
Studying health effects using in vitro methods
In a review article published on July 25, 2023, in the journal Environment International, Valérie Forest and Jérémie Pourchez from the University Jean Monnet, Saint-Etienne, France, discussed if and how potential human health impacts of micro- and nanoplastics can be evaluated by using in vitro models like the one used by Hussain and co-authors.
The authors pointed out that plastic particles differ from other chemicals in certain characteristics which have to be considered in the design of in vitro experiments. For instance, some plastics have a low density and, thus, will float on a medium’s surface and not come in contact with the cells adhering to the bottom of the test plates. Therefore, the concentration the cells are actually exposed to may be lower than expected. The authors discuss several issues related to studying microplastics, before proposing solutions based on a literature survey. In the case above, a solution would be to model the concentration of particles the cells have actually come into contact with. Moreover, the scientists provide perspectives for further research “on the in vitro evaluation of micro- and nanoplastics toxicity, underlining the importance of using standardized protocols for comparison purposes and samples and experimental conditions more representative of real-life exposure.”
Forest, V. and Pourchez, J. (2023). “Can the impact of micro- and nanoplastics on human health really be assessed using in vitro models? A review of methodological issues.” Environment International. DOI: 10.1016/j.envint.2023.108115
Hussain, K. A. et al. (2023). “Detection of Various Microplastics in Patients Undergoing Cardiac Surgery.” Environmental Science & Technology. DOI: 10.1021/acs.est.3c01942
Montano, L. et al. (2023). “Raman Microspectroscopy evidence of microplastics in human semen.” Science of the Total Environment. DOI: 10.1016/j.scitotenv.2023.165922
Yang, Y. et al. (2023). “Detection of Various Microplastics in Patients Undergoing Cardiac Surgery.” Environmental Science & Technology. DOI: 10.1021/acs.est.2c07179
ScienceDaily (July 20, 2023). “Billions of nanoplastics released when microwaving baby food containers.”
This article was originally published by Lisa Zimmermann at the Food Packaging Forum.