Microplastics and phthalate esters in tropical estuaries of Hainan Island, China: Spatial distribution and interrelationship patterns

Abstract

Microplastics (MPs) and phthalate esters (PAEs) are widespread plastic-related contaminants in aquatic environments, yet their co-occurrence in tropical estuarine ecosystems remains limited. In this study, MPs and PAEs were simultaneous investigation in surface seawater and sediments from 65 sites across 10 estuarine regions of Hainan Island, China during the spring dry season of 2024. MPs were examined using stereomicroscope followed by micro-Fourier Transform Infrared Spectrometer (μ-FTIR), while the PAEs were analyzed by solid-phase extraction and Gas Chromatography-Mass Spectrometry (GC-MS). Both MPs and PAEs were widely detected throughout the study area. In seawater, MPs abundances and PAEs concentrations ranged from 1.1 to 15.1 items/L (mean: 5.3 ± 2.6 items/L) and 158.2 to 2317.6 ng/L (mean: 1023.7 ± 448.3 ng/L), respectively. In sediments, MPs abundance and PAEs concentrations ranged from 60 to 1053.3 items/kg dry weight (dw) (mean: 264.6 ± 189.1 items/kg dw) and 45.8 to 863.7 μg/kg dw (mean: 337.9 ± 179.6 μg/kg dw), respectively. In terms of composition, polyethylene terephthalate (PET) and cellulose were detected as primary MP polymers, while di (2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) were identified as major PAE congeners in both seawater and sediments. Correlation analysis revealed significant positive correlations between the abundances of MPs and the concentrations of PAEs in both seawater and sediments, with a stronger correlation observed in sediments (r = 0.57, p < 0.01) than in seawater (r = 0.40, p < 0.01). Overall, these findings provide a regional dry-season baseline for the co-occurrence of MPs and PAEs in Hainan Island's estuarine–coastal environments and support future monitoring and source-oriented pollution management.