How Much Microplastics Are We Ingesting?: Estimation of the Mass of Microplastics Ingested.

Tuesday, 11 June 2019

Kala Senathirajah and Thava Palanisami

The University of Newcastle, Australia

Summary of the study methodology

Microplastics have been defined as plastic particles with an upper size limit of 5 mm. Microplastics are of significant concern as they may pose a direct threat (by ingestion), or indirect threat (by acting as potential stressors or vectors of contaminants) to humans. Mismanagement of primary and secondary microplastics may be accumulated and/or transferred through the food chain and reach our digestive system and bloodstream. This paper attempts to provide a snapshot through a systematic review of the published literatures, and calculate an ingestion rate for humans considering various exposure pathways. This study analysed the available literature as a method for data collection and synthesis to allow for an estimation of the amount of microplastics ingested by humans. A critical research of the available literature and subsequent unit normalized calculation of the amounts of microplastics ingested by humans through various exposure pathways suggest that on average, humans may be ingesting as much as 5 g/week of microplastics.

Several databases were interrogated to obtain the most recent relevant publications. The metadata was extracted and recorded. The literature review presented information on many different methods for sampling and analysing microplastics to identify and quantify them. Reporting units also varied greatly among studies. In order to compare the data, several conservative assumptions were made. The conservative approach was adopted to minimise the risk of over-predicting and from alarming the public, or risking incredulity from decision-makers and other stakeholders. The data was extrapolated to infill and populate missing data to derive a total number of microplastic particles (particles) and total mass particles (kg) to then allow for the calculation of ingestion rates (kg/week/person) based on estimated individual particle mass (kg/particle). A second approach using the density and volume of the particles was adopted to assess the impact of volume weighting in determining the calculated average mass of each microplastic particle.

Due to the limited data available on the particle size distribution of microplastics, an average mass per particle in the size range 0-1mm was adopted to represent the average particle mass for each microplastic particle ingested. It was decided that this study would discount the mass of particles >1mm for the calculation of ingestion rate.

The literature was interrogated for several counts of microplastics in staples such as water, shellfish, fish, salt, beer, honey and sugar. This project did not take into account other possible direct ingestion sources such as the honey, fish, sugar (for which data was collated) or rice, pasta, bread, milk, utensils, cutlery, toothpaste, toothbrushes, food packaging and a multitude of other sources that would only add to the amount consumed. As such, there is confidence that based on the literature reviewed and subsequent analysis performed that up to 5 g/week of microplastic particles is potentially ingested by humans. Having said that, it should be stressed that the amount of the microplastics ingested by an individual will depend on a combination of parameters that is highly variable not only pertaining to the characteristics of the microplastics but also to each’s age, size, geographic location, demographics of the location, nature of development and life-style options.

This study is being reviewed for publication; the full methodology and supplementary data will be available upon acceptance.

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