Distribution, Characteristics, and Potential Health Risks of Microplastics in National Coastal Highway Road Dust, Northern Mindanao, Philippines

Microplastics (MPs) are a growing environmental problem, especially in urban areas with high human activity. Urban roads are important transport routes for MPs into aquatic and atmospheric systems, making understanding their occurrence, characteristics, and deposition in road dust is crucial. This study investigated the abundance, morphology, and polymer type of MPs in coastal road dust from three major cities in the southern Philippines: Cagayan de Oro, Iligan, and Ozamiz City. Results showed that MP abundance in road dust ranged from 180 – 780 n/kg. The MP abundance at the downtown site of each city was significantly higher than at other sites. The morphology of MP was mainly characterized by fragments (77.7%), blue color (32.5%), and small size (< 1000 μm; 68%). Polyolefin polymers were the main polymers (60.9%) identified. Microplastic abundance was positively correlated with population density, but not significantly correlated with traffic volume. This reflects that MP in road dust in the study area may mainly come from the degradation of daily consumption-related products. In contrast, the contribution from road and automobile-related sources is low. Notably, road- and traffic-related MPs were found to be often extremely hazardous, leading them to be key to the high hazard risk of MPs despite their lower prevalence (< 6.2%). Road dust MPs in the three cities showed moderate diversity and high hazard, among which Iligan City (industrial city) had a relatively high diversity and hazard index. Overall, this study confirms MP accumulation and hazard risks in Philippine road dust—highlighting the importance of MP studies in growing and urban cities for MP pollution management and mitigations.