Atmospheric and indoor microplastics deposition in the city of Bangkok, Thailand

MPs abundance is a severe issue globally owing to its presence in all parts of the environment. Compared to other environmental compartments, atmospheric MPs are in their infancy state of research and analysis. Atmospheric MPs are a severe issue as they can contaminate water bodies, agricultural land, drinking water and wastewater treatment plants. Similarly, indoor MPs are also a serious concern as an individual spends the majority of time in the indoor environment. The results from this research highlight the abundance of MPs in terms of count, size, morphology, and polymeric type in Thailand's indoor and outdoor environments. In this study, a passive sampling method, followed by digestion, density separation, and Nile red tagging, was employed to estimate MPs abundance in outdoor and indoor air in Bangkok, Thailand. The lower detection limit was 53 µm. Five sites varying in monthly expenditure per dormitory, occupant number, air conditioner/fan use, and window use patterns were selected for indoor sampling. Outdoor sites comprised urban, semi-urban, and industrial sites. The relationships between MPs count and meteorological parameters were also examined for outdoor sites. This study revealed an average indoor MPs abundance of 154 ± 62 particles/square meter/day (p/m2/d). Fragments dominated other shapes in indoor air (68%). The µ-FTIR analysis identified 20 polymers, with polypropylene as the dominant polymer type in indoor sites. It is speculated that MPs come from plastic items, textiles, paints, and coatings in indoor environments. The monthly expenditure and number of occupants strongly correlated with the indoor MPs deposition rate. Similarly, the use of air conditioners showed a strong correlation, whilst the use of the fan was negatively correlated with MPs abundance. Regarding indoor MPs exposure, the estimated number of MPs that may enter the human body via inhalation and ingestion was estimated to be 399 particles/year respectively. The MPs deposition rate in the lab was observed to be 286 ± 104 p/m2/d. Fragments dominated other shapes in the lab too. Polymeric analysis revealed only 4 polymers, with polyethylene as the dominant type. An average MPs deposition rate of 103 ± 52, 262 ± 100, and 263 ± 128 p/m2/d was observed at urban (Chulalongkorn), semi-urban (SIIT), and industrial (Bangkadi) sites, respectively. Fragments dominated other shapes in all the outdoor sites (urban (90%), semi-urban (75%), and industrial (80%)). Polypropylene dominated other polymers at SIIT and Bangkadi, whilst polyethylene was the most dominant polymer at Chulalongkorn. Spectroscopic analysis revealed 15, 7, and 15 different polymers at SIIT, Bangkadi, and Chulalongkorn, respectively. It is speculated that outdoor MPs come from environmental degradation of plastic wastes, paints, and coating in infrastructures. All the considered meteorological parameters depicted some correlation (very strong-moderate) with the outdoor MPs abundance. However, the severity of these parameters varied within the sites (ground vs. height) and among the sites (urban vs. semi-urban vs. industrial). Our results show that MPs are ubiquitous in indoor and outdoor environments with possible human exposure. Fragments are dominant shapes in both indoor and outdoor environments. Polypropylene and polyethylene are the commonly observed polymers in both environments. Plastic items, paints, and coatings are the primary sources of the MPs in indoor and outdoor environments. It is recommended that future studies consider the analysis of smaller MPs (down to 1 µm). Furthermore, the factors affecting indoor and outdoor MPs deposition rates be more deeply investigated by considering samples for a more extended period. The presence of MPs in human lungs be examined to confirm MPs inhalation through breathing. Moreover, the toxicity of MPs (shape, size, and polymer type) is a new field awaiting further research and analysis. It is recommended to digest the samples for MPs analysis in indoor environments.