Multidimensional Assessment of Microplastic Pollution in Mangrove Wetlands: Driving Mechanisms, Carbon Contribution, and Ecological Risk

Microplastics
(MPs) have emerged as pervasive contaminants
in mangrove
ecosystems, yet their driving factors, carbon contributions, and ecological
risks remain poorly understood. This study systematically investigated
MP pollution across six functional areas in two representative mangroves
of Hainan, China. MPs were ubiquitous in both water and sediments,
with higher abundances in fishing and aquaculture zones than in tourist
protection and residential zones. Sediments in the low-tide zone acted
as major MP sinks compared to those in the high-tide zone. PP was
the main polymer type, and fibers dominated in water and fragments
in sediments. The studied mangroves exhibited a moderate level of
MP pollution on a global scale. Partial least-squares path modeling
(PLS-PM) identified vegetation density, nutrient enrichment, and heavy
metals as key drivers. However, its effects vary between sediment
and water environments. Integrated ecological risk indices indicated
generally low-to-middle risk with localized pollution hotspots in
estuarine and aquaculture areas. MP mass concentrations averaged 5.69
mg/m3 in water and 4.73 mg/kg dw in sediments, contributing
0.0050–0.0147% to sedimentary organic carbon as an emerging
inert carbon pool. In addition, it is estimated that the study area
receives an additional annual MP load of 3457.08 kg and an MP carbon
load of 2795.83 kg. These findings provide a comprehensive understanding
of MP behavior and environmental effects in mangrove wetlands, offering
a scientific foundation for targeted mitigation and long-term monitoring
of coastal plastic pollution.