Spatial heterogeneity of microplastics and ecological risk assessment based on detection of seawater and fish in typical coastal region in Hainan

To clarify spatial heterogeneity and ecological risks of microplastics (MPs) in typical coastal areas of Hainan, address regional research gaps, and support pollution control and ecological protection, this study systematically analyzed microplastic distribution in surface seawater and fish guts across three coastal regions Xin Cun (XC), Qing Lan Gang (QLG), Ying Ge Hai (YGH) of Hainan Island from April to July 2024. Surface seawater microplastic concentrations varied significantly among regions with average abundances of 3.36 items/L (XC), 4.65 items/L (QLG), and 2.71 items/L (YGH, the lowest); concentration ranges were 1.07-8.73 items/L (XC), 1.90-8.83 items/L (QLG), and 1.53-6.50 items/L (YGH). Compositional characteristics showed regional specificity: XC and QLG were dominated by black (46.47 % and 55.54 %) and fibrous (60.67 % and 63.09 %) MPS while YGH featured polystyrene (PS, 25.93 %) as the primary material. MPs were ubiquitous in fish guts with average abundances highest in XC (23.97 items/individual) followed by YGH (11.25 items/individual) and QLG (8.53 items/individual). Siganus guttatus in XC exhibited the highest microplastic content at 93.33 items/individual, significantly exceeding conspecifics in YGH (33.00 items/individual) and QLG (26.00 items/individual). Intestinal MPs were primarily black or white, fibrous or foamy, and sized 0.01-2 mm. Microplastic concentrations in water correlated significantly positively with their abundance in fish guts, particularly in XC and QLG where strong correlations were observed for most fish species. Ecological risk assessments classified XC as high risk, YGH as medium risk, and QLG as dangerous risk; most sampling sites showed PERI values trending toward dangerous risk. Fish microplastic polymer risk indices ranged 3-20 with Siganus guttatus in all three regions classified as Class II risk. Comprehensive assessment revealed region-specific impacts of microplastic pollution on fish and their ecosystems with notable threats in XC and QLG. Strengthened monitoring and management of microplastic pollution in Hainan's coastal waters are needed to support evaluations of microplastic impacts on marine ecosystems.