Microplastic pollution in Vietnamese sandy beaches: Exploring the role of beach morphodynamics and local management.

Microplastics are omnipresent, raising significant concerns in marine environments. This study investigates how different beach morphodynamics and local management practices (i.e. pollutant sources, tourism, beach cleaning) influence microplastic pollution in sandy beach sediments in Vietnam by comparing tidal zonation patterns across three beaches with varying slopes and management approaches. Environmental variables (Chlorophyll a, total organic material, grain size) and microplastics polymer composition, size and concentrations were measured at the high and the low water marks of each beach. Microplastics were found on all beaches, with high variation. The dominance of denser MPs, like PET, on reflective beaches coupled with the prevalence of lighter MPs in the high tidal zone, demonstrates the role of beach morphodynamics and tidal flows in shaping microplastic distributions. Furthermore, local waste management practice and input from tourism activities can contribute to the patchy microplastics distribution. For instance, the larger size of microplastics at the beach with most macrolitter suggests the role of fragmentation down to microplastics as a pollution source which can pose risks to benthic ecology and human health in regional communities. Our findings highlight a complex interplay between beach morphodynamics and local pollution sources in driving microplastic distribution. Addressing the issue of MPs pollution on sandy beaches will therefore require targeted management strategies that reduce pollution sources in relation to natural processes that set the deposition of microplastics in beach sediments.