While everyday, people are exposed to microplastics from food, water, beverages and air, the extent to which these accumulate in the human body - and the potential health risks - have remained unknown. Now, a new lifetime microplastic exposure model has been developed that can account for variable levels from different sources and in different populations, researchers report in the ACS journal Environmental Science & Technology on 16 March. The new model indicates a lower average mass of microplastic accumulation than previous estimates.
Microplastics are ingested from a variety of sources, such as bottled water, salt and seafood. Once in the human body, their fate and transport are largely unknown. Next to possibly causing tissue damage and inflammation, microplastics may also form a source of carcinogens and other harmful compounds that leach from plastic into the body.
Previous studies have tried to estimate human exposure to the particles and their leached chemicals, but they have limitations, including discrepancies in the databases used, a failure to consider the entire microplastic size range and the use of average exposure rates that do not reflect global intakes.
Nur Hazimah Mohamed Nor, Albert Koelmans and colleagues wanted to develop a comprehensive model to estimate the lifetime exposure of adults and children to microplastics and their associated chemicals. The model was comprised of two components: a Plastics Model , to evaluate the exposure to and accumulation of microplastics in the body, and a Chemical Model. For the chemical model, four representative chemicals were investigated: (1) BaP, (2) DEHP, (3) PCB126, and (4) lead.
“Previous risk assessments that evaluate the role of microplastics as chemical vectors in humans have so far assumed worst case scenarios in their calculations, with 100% instantaneous leaching of chemicals,” the researchers write.
To make their model, the researchers identified 134 studies that reported microplastic concentrations in fish, mollusks, crustaceans, tap or bottled water, beer, milk, salt and air. They performed corrections to the data so that they could be accurately compared among the different studies. Then, the team used data on food consumption in different countries for various age groups to estimate ranges of microplastic ingestion. This information, combined with rates of microplastic absorption from the gastrointestinal tract and excretion by the liver, was used to estimate microplastic distribution in the gut and tissues.
The model predicted that, by the age of 18, children could accumulate an average of 8,300 particles (6.4 ng) of microplastics in their tissues, whereas by the age of 70, adults could accrue an average of 50,100 microplastic particles (40.7 ng). The estimated amounts of four chemicals leaching from the plastics were small compared with a person’s total intake of these compounds, the researchers concluded.
“We conclude that the contribution of the MPs to chemical intake is small to negligible for the four representative chemicals investigated in this study and yet still not substantial for BaP (∼17%) and lead (∼20%) at the 97.5th percentile of the amount of chemicals leached,” they write.
These data suggest that prior studies might have overestimated microplastic exposure and possible health risks, but it will be important to assess the contributions of other food types to ingestion and accumulation, the researchers say.
The authors acknowledge funding from Yayasan Mendaki, the Prophet Muhammad’s Birthday Memorial Scholarship Fund Board and the Aquatic Ecology and Water Quality group of Wageningen University