Microplastic Pollution in China’s Inland Waters Surpasses Coastal Seas under Anthropogenic Pressures

Microplastics are emerging as a global environmental
challenge,
yet the role of inland waters in shaping their distribution and risks
has remained largely overlooked. By synthesizing over 13,000 records
from 500 studies across China’s 10 river basins and 4 seas,
we show that inland waters are not only conduits but also dominant
sinksrivers exhibit 0.9–7.7 MP L–1 and reservoirs exhibit 1.2–8.3 MP L–1,
both significantly exceeding adjacent seas (0.1–2.2 MP L–1). Fibers and fragments dominate (>60%) morphological
profiles, while polymer compositions mirror intensive human activities,
linking urban emissions and agricultural plastic use directly to freshwater
burdens. Machine learning (R2 = 0.85)
reveals that population density and night-time lights are the strongest
predictors of abundance, surpassing climatic and geographic variables,
underscoring the primacy of anthropogenic pressures in shaping spatial
heterogeneity. Ecological risk assessments further demonstrate that
33.1% of freshwater samples exceed medium-risk thresholds (RQ >
0.1),
and 2.4% reach high risk (RQ ≥ 1), in stark contrast to uniformly
low-risk marine sites. These findings challenge the ocean-centric
paradigm of plastic pollution, positioning inland waters as critical
hotspots of accumulation and risk, and highlight the urgent need for
integrated, source-to-sink management strategies across the land–freshwater–ocean
continuum.