Zhong Pan

Groundwater in shallow coastal aquifers may receive microplastics (MPs) from coupled land-use and surface-water systems, yet the factors controlling their occurrence remain poorly constrained. Here, we quantified MPs in 12 samples from a coastal alluvial aquifer along the Fujian coast, southeastern China, including 6 groundwater (GW) wells, 4 shallow beach pore-water (PW) sites, and 2 shallow riverbank pore-water (RW) sites, using an Agilent 8700 LDIR system with a 10 μm detection limit. Total MP abundances ranged from 107 to 1,262 items L-1 (mean 526), with higher values generally observed in coastal GW wells. Fibers and irregular fragments dominated, and PP, PE, PS, PET, and PVC were the main polymers. A synthesis of 48 published groundwater MP studies indicates that concentrations in the study area fall among the higher values compiled in the current literature. To examine potential controls, we combined multi-scale land-use metrics derived from ESA WorldCover and OSM with Pearson correlation, geographically weighted regression, and distance-based analyses. Cropland and surface-water fractions were positively associated with MP abundance, whereas urban and forested areas showed weak or negative relationships. MP abundance also declined with increasing distance from major rivers and embayments, while distance to urban centers showed limited explanatory power. These results suggest that, in shallow coastal alluvial aquifers, groundwater MPs are linked more closely to land-use structure and groundwater–surface water connectivity than to simple urban proximity. This study provides preliminary evidence that coastal plains may represent vulnerable accumulation zones for groundwater microplastics.

Microplastics (MPs) serve as potential carriers for heavy metals in aquatic environments; however, their adsorption behavior within complex sedimentary matrices, particularly under environmental aging, remains poorly understood. This study investigates the effects of plasma and ultraviolet (UV) aging on the adsorption of mercury (Hg2+) by polystyrene (PS), polyvinyl chloride (PVC), and rubber in aquatic and sedimentary environments. Aging treatment significantly increased oxygen-containing functional groups, hydrophilicity, and negative surface charge of the MPs, resulting in a pronounced enhancement of Hg2+ adsorption capacity in aquatic environments, with UV-aged MPs exhibiting substantially elevated adsorption. In contrast, Hg2+ adsorption by MPs was significantly inhibited in sedimentary environments due to competitive interactions with sediment components (e.g., iron oxides and organic matter) and physical shielding of particle surfaces caused by heterogeneous aggregation. Adsorption kinetics of the MP-sediment system followed a pseudo-second-order model, while isotherm analysis indicated the coexistence of monolayer and multilayer adsorption. X-ray photoelectron spectroscopy (XPS) further revealed that oxygen- and nitrogen-containing functional groups actively participate in Hg2+ binding and partially facilitate its reduction to Hg+. Overall, these findings demonstrate that although environmental aging enhances the intrinsic mercury adsorption potential of MPs, their effectiveness as mercury carriers in sediments is substantially constrained by matrix interactions and aggregation effects. This study provides critical insights into the environmental fate and risk assessment of MP–heavy metal co-pollution, underscoring the necessity of explicitly incorporating sediment matrix effects into environmental risk evaluations.