Household indoor microplastics within the Humber region (United Kingdom): Quantification and chemical characterisation of particles present

Highlights

• Household levels of MPs averaged 1414 MP m⁻² day⁻¹ ± 1022 (mean ± SD).

• Polyethylene terephthalate was in 90% of samples and accounted for 62% of MPs.

• Small (5–250 μm) fibers were most abundant and a size relevant to lung intake.

Abstract

Knowledge regarding the presence of suspended microplastics (MPs) within the air is lacking, especially indoors, yet the importance of indoor air quality and human health is rising. This study is the first to report MPs within multiple homes over a 6-month period, with concentrations exceeding previous outdoor studies. Twenty households, within the City of Hull and Humber region, U.K., were passively sampled, each month, collecting atmospheric fallout at head height for subsequent particle quantification, characterisation and μFTIR validation (n = 3061). A household average of 1414 MP m⁻² day⁻¹ ± 1022 (mean ± SD) was observed. Smaller (5–250 μm), fibrous, particles were the most abundant (90%), representing types most likely to enter the human body and cause physiological harm. Polyethylene terephthalate (PET) was present in 90% of samples and accounted for 62% of MPs. Additionally, polyamide (PA) and polypropylene (PP) were common. Results indicate that humans are exposed to significantly (1–45 times) higher concentrations, and ranges, of MPs within homes compared with the outdoor environment. In conclusion, the size range and types of MPs observed will inform laboratory experiments, using either human tissue culture or other approaches. This will allow determination of the wider implications on human health using realistic levels and representative types of indoor MPs.

Introduction

Plastic products are used in countless applications; from food packaging, textiles and electronics, to building, construction and medical devices (Geyer et al., 2017; Wright and Kelly, 2017). Yet, plastic waste mismanagement is stated to be a key burden in environmental literature (Murphy, 2017). Of the predicted 6300 million metric tons of global plastic waste generated prior to 2015, 79% has been estimated to aggregate within landfills and the environment, and only 9% recycled (Geyer et al., 2017). This results in the introduction of primary plastics, secondary degradation plastics and chemical leachates into aquatic, terrestrial and atmospheric compartments (GESAMP, 2015), and ultimately leads to global MP pollution. Research has previously been directed more towards routes of MPs into the environment and prevalence (Horton and Dixon, 2017), as well as dietary exposure via salt, seafood and drinking water (Catarino et al., 2018; bDanopoulos et al., 2020, aDanopoulos E et al, 2020). However, there is now an emerging concern surrounding MP inhalation as another human exposure route (Wright and Kelly, 2017; Gasperi et al., 2018; Prata et al., 2020). Consequently, gaining a holistic view of MP pollution and human exposure is of increasing importance.

Since their initial identification (Dris et al., 2015), MPs have been consistently reported within atmospheric samples. MPs have been captured both passively and actively (Table S1), as well as within deposited dust samples, demonstrating their ubiquity (Abbasi et al., 2019; Huang et al., 2020). MPs (defined herein as between the size ranges of 1 μm and 5 mm (Hartmann et al., 2019)) are not yet considered an atmospheric pollutant. They are considered an emerging contaminant of concern and have been reported as a constituent of particulate matter (PM). Questions relating to human exposure rates and health consequences have since arisen (Wright and Kelly, 2017; Prata, 2018; Abbasi et al., 2019; Prata et al., 2020). Passively sampled MPs are reported within literature as units of MPs m⁻² day⁻¹, with publications from France (ranging from 53 to 365 m⁻² day⁻¹) China (33-9900 m⁻² day⁻¹), Germany (137-512 m⁻² day⁻¹), and most recently, the UK (3-771 m⁻² day⁻¹) (Dris et al., 2015, 2016; Cai et al., 2017; Allen et al., 2019; Klein et al., 2019; Wright et al., 2019; Zhang et al., 2020). In contrast, MPs captured actively are expressed in units of MP m⁻³, with reports from France (0-59 m⁻³), Denmark (9 m⁻³), China (0-5 m⁻³) and America (1-13 m⁻³) (Dris et al., 2017; Abbasi et al., 2019; Liu et al., 2019a, Liu et al., 2019b; Li et al., 2020). To date, just four studies worldwide report on MPs within the home (Dris et al., 2017; Vianello et al., 2019; Zhang et al., 2020; Gaston et al., 2020). It is important to note that environmental sampling (duration, location, meteorological conditions, sample number), sample processing steps (digestion, purification), microscopic analyses (observational criteria, size and shape categories) and chemical analyses methodologies all vary, and it is difficult to conduct meaningful inter-study comparisons. Despite this, the majority of studies evidence that MPs increase in concentration with decreasing particle size (until an observational limit is reached) (Allen et al., 2019). MPs are prevalent in locations of high human activity e.g. urbanised city centres (Dris et al., 2016), and tend to be fibrous (Dris et al., 2016; Liu et al., 2019a). One passively sampled study recorded indoor atmospheric MP levels ranging from 1500 to 9900 MP m⁻² day⁻¹, depending on the room, a rate exceptionally higher than outdoor studies (Zhang et al., 2020). MP studies that have reported actively sampled indoor MP levels (ranging from 1 to 59 m⁻³) (Dris et al., 2017; Vianello et al., 2019), again, exceed that of outdoor concentrations (which range from 0 to 6 m⁻³) (Table S1). The significance of indoor air quality is highlighted by the fact that humans spend up to 90% of their time indoors (Klepeis et al., 2001) and as much as 60% within their homes (NICE, 2020). Whilst the health effects of exposure to indoor MPs are not yet defined, indoor PM has been linked to a number of health impacts including a decline in respiratory and cardiovascular health (Royal College of Physicians and Child Health, 2016) as well as specific MP types inducing toxic impacts in recent human lung cell culture exposure studies (Goodman et al., 2021; van Dijk et al., 2021).

To date, there are many unknowns: from the chemical composition, size or shape of the MP, to any chemical leachate or adsorbed pollutants. The possibility of MPs entering the human body and impact of such exposure on health is of increasing concern. This study aims to provide knowledge surrounding the indoor MPs that humans are most likely exposed to, by quantifying concentration rates, and determining particle dimensions, shapes and chemical composition.