Microplastics and heavy metals in a tropical river: Understanding spatial and seasonal trends and developing response strategies using DPSIR framework.

Microplastics (MPs) have become an increasingly popular topic in recent years due to the growing concern about their impact on human health and the environment. Rivers in Southeast Asia are the dominant source of plastics and MPs into the environment; however, research on MPs in rivers from the region is insufficient. This study aims to investigate the impacts of spatial and seasonal variations on the distribution of MPs with heavy metals in one of the top 15 rivers releasing plastics into oceans (Chao Phraya, Thailand). Findings from this study are analyzed using the Driver-Pressure-State-Impact-Response (DPSIR) framework for proposing strategies to minimize plastic and MPs in this tropical river. Spatially, most MPs were detected in the urban zone, while the lowest was in the agricultural zone. Also, MP levels in the dry season are higher than at the end but lower than at the beginning of the rainy season. MPs with fragment morphology were mainly found in the river (70-78 %). Polypropylene was found with the highest percentage (54-59 %). MPs in the river were mostly detected in the size range of 0.05-0.3 mm (36-60 %). Heavy metals were also found in all MPs collected from the river. Higher metal concentrations were detected in the agricultural and estuary zones in the rainy season. Potential responses, including regulatory and policy instruments, environmental education, and environmental cleanups, were drawn from the DPSIR framework.