Plastics are ubiquitous in our environment. Much has been made about the increasing amounts all around us, in intended and unintended places. A new study indicates that one of those unintended places is now our bloodstream. This is the first step to understanding their potential toxicity, so it pays us to look carefully at what the scientists did and did not find.
It is difficult to detect the tiny amounts of plastic lurking within our bodies. If the truth is known, “validated methods sensitive enough to detect trace amounts of especially the small (<10 μm) size fractions of plastic particles in biological tissues have been lacking.” While waiting for such methods to develop, the researchers kicked it “old school,” using the chemical signature of specific plastics when burned. Furthermore, they borrowed a concept from the studies of air pollutants, defining concentrations of these plastics based upon the size, much as we discuss “pollutants” as PM2.5.
It’s a Small World
The size range of the particles the researchers studied had an upper limit of 514,000 nanometers (nm) and a lower limit of 700 nm. The upper limit is established by the inner diameter of the needle used to draw blood, the lower limit by the filter used to collect the study samples. As a biologic comparator, a red blood cell is 7000 nm wide, and a typical capillary is between 5-10,000 nm in diameter – red blood cells pass through the smaller capillaries because they are bendable. More importantly, capillaries leak molecules no larger than 5 to 10 nm in size.
The researchers looked at five of the most widely used plastics with applications in food packaging, textiles, and other products we deal with daily. They were
- poly(methyl methyl acrylate) – used in dental and orthopedic surgery
- polypropylene – a high demand material
- materials containing polymerized styrene
- polyethylene and polyethylene terephthalate (PET) – again, high demand materials.
They made use of blood samples taken from 18 random donors. These blood samples were washed and sent through a 700 nm filter. The collected mass was then pyrolyzed (a chemical term for combusted). The consequent “thermal degradation products,” the signatures of the plastics, were then measured. The researchers went to great pains to eliminate and control for background contamination by their collection equipment and used the pyrolysis results of blanks to subtract any thermal degradation products from their equipment. They also “spiked” blood samples with known amounts of these plastics to demonstrate “that the method could extract, identify and quantify low ppm concentrations of major polymers applied in contemporary plastic.”
- 77% of the donors had detectable amounts of these plastics
- For the three most detected polymers, the number of donors with values great enough to quantify were 5 for polyethylene (23% of all donors), 8 for polymerized styrene (36%), and 11 for PET (50%).
- The frequency of non-detects measured also varied per polymer type. The percentage of all donors for whom the analyte was consistently less than the level of detectability was 91% for methylmethacrylate, 82% for polypropylene, 27% for polyethylene, 9% for PET, and 5% for polystyrene.
The researchers performed a duplicate analysis of samples because the concentrations reported were very close to the limits of detection. There were no detectable levels in roughly a third of the repeat sampling involving PET or polyethylene. I point this out to show the rigor of the scientist’s work and the uncertainty of the quantitative, not the qualitative findings.
Overall, the mean amount of plastics identified was 1.6 μg total plastic particles/ml blood. Like the methodology for air pollutants, the analytic method does not allow for the counting of the number of particles, only their total mass. This is a nuanced difference, but it may be sufficient to recognize that particles are more gist than reality. Suppose this concentration is equally spread across the total blood volume, a reasonable assumption made by the researchers. In that case, we are looking at a total of about 8 mg of plastic in the mythical average adult.
“The data in this pilot dataset should be interpreted as a clear signal that such polymers can be present in human blood, as evidenced by the quantifiable concentrations after blank correction, rather than an in-depth assessment of internal exposure in individuals.”
They point out that the dwell time and fate of these “particles” in our bodies are unknown. These numbers are a summation of all of our potential exposures – from PET in lip gloss to polyethylene in toothpaste and polystyrene in tattoos. They hypothesize that the primary uptake is either by ingestion or inhalation, but that has yet to be proven; we only know that plastics are within us.
They end on this note:
“A human health risk assessment (HRA) for plastic particle pollution is currently not possible due to lack of data on both toxicological hazard and human exposure.”
Source: Discovery and quantification of plastic particle pollution in human blood Environment International DOI: 10.1016/j.envint.2022.107199
