Spatial distribution and health risk assessment of microplastics in urban street dust, northeastern Iran

Abstract

Plastic pollution has become a major environmental concern, mainly because of the formation of microplastics (MPs) that persist in urban environments and pose potential health risks. This study investigated the occurrence, characteristics, and potential human health risks of MPs in street dust from Mashhad, Iran. Street dust samples collected from different functional areas of the city were processed by ozonation to remove organic matter, followed by ZnCl₂ density separation, filtration, and microscopic analysis to isolate and quantify MPs (particles per gram of dry dust) and evaluate health risks. The results showed a strong association between MP concentrations and both population density and traffic intensity, with values ranging from 90 ± 32 particles/g in low-density areas to 530 ± 21 particles/g in high-density zones. Fragments (61.2%) and black particles (53.5%) were predominant, and 63% of the particles were smaller than 100 µm. The major polymer types identified were low-density polyethylene (LDPE), polypropylene (PP), styrene–butadiene rubber (SBR), and polyethylene terephthalate (PET). The estimated daily ingestion of MPs was 307 particles for adults and 1,790 particles for children, whereas inhalation exposure was comparatively lower. Overall, this study provides the first quantitative assessment of MP pollution and related health risks in street dust from Mashhad, emphasizing the need for improved urban management and public awareness to mitigate this emerging environmental problem.