Measuring and evaluating the risk of harm from microplastics in household dust

Microplastics (MPs) have recently been recognized as an emerging contaminant of concern. Microplastics have received little attention in the atmosphere, most notably indoor environments, where people spend up to 90 % of their time. Atmospheric environments can be both a source and a sink of MPs. This thesis asks the following research questions: (1) comparing efficacy of available analytical methods and developing a standardised method for MPs analysis; (2) deposition rate and characterisation of MPs in household dust; (3) the influence of household conditions and economy on deposition rate of MPs; (4) health risk of exposure to deposited MPs; and (5) measures and strategies that can be applied to reduce the risk of harm to MPs.

The thesis chapters comprise a review of MPs sampling, sample treatment, and analytical methods used in atmospheric MPs studies. These methods are including most conventional methods of MPs studies such as microscope Fourier Transform Infrared Analysis (μFTIR), Focal Plane Array FTIR, μRaman and a new method of Laser Direct Infrared (LDIR) spectroscopy. This review found that even though MPs is ubiquitous in the atmosphere, there is still a lack of technology that can be used to obtain accurate measurements. Despite the lack of a valid standard method in MPs studies, a method was first developed for the study based on the nature and number of the samples. 

This thesis evaluates the prevalence, source and type of MPs in Australian homes for the first time. Human exposure via inhalation and ingestion pathways was modelled. The developed method was applied to a sampling program distributed across 29 countries to better understand international MPs deposition rates and associated human health risks. Using household metadata, we can identify factors that contribute to MPs prevalence and exposure in both studies. In addition, in international study economy of countries was hypothesised as an influencing factor on MPs deposition rate. 

Using microscopic and μFTIR analysis to examine samples, the following findings were achieved: (a) MPs were abundant in all homes and assign 39 – 46 % depositional rate of fibres in household dust; (b) vacuum cleaner use and type of flooring were the main influencing factors on deposition rate and composition of MPs in household environments. This result can define the relevant strategies for mitigating MPs deposition rate; (c) Children in low income countries were exposed to the highest rate of MPs intake and can be suffered from the relevant health risk. 

Overall, the findings presented in this thesis contribute to the growing body of research examining the environmental and human health risks of MPs. Specifically, this thesis has developed and tested and applied a new standardised method for monitoring and then assessment of MPs exposure in homes at an international scale, where human exposure is greatest. As the best practical estimate so far, the research findings can be used as a benchmark for future studies of this type. Moreover, the study also identifies possible solution/intervention strategies to reduce exposure harm.