Heavy metals are typical pollutants in the environment and microplastics are relatively newly recognized environmental pollutants, with their coexistence potentially compounding pollution and ecological risks. In this study, we investigate the contents and morphological characteristics of microplastics and heavy metals (Cu, Cd, Pb, Zn, and Cr) in the estuarine sediments of Poyang Lake and the Yangtze River as a means of exploring the relationship between them. The results showed that the abundance of microplastics ranged from 356 n·kg-1 to 1452 n·kg-1, with an average abundance of 982.33 n·kg-1 in the dry sediments. Microplastics were identified as being of three main types:fragments, fibers, and films, whereby fragments were the most dominant type found and accounted for 48.23% of the total microplastics in the sediments. The main color of microplastics in the sediments was chromatic, and the particle size of most microplastics was<1 mm. The major polymer components were polyethylene (PE), low density polyethylene (LDPE), and polyethylene (PP). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) results indicated that the surfaces of microplastics were rough, porous, cracked, and torn, and that the five heavy metals were found on the surfaces of different microplastics. These heavy metals accumulated to different degrees in the estuarine sediments, and redundancy analysis indicated that environmental factors[including the total organic carbon (TOC), pH, electrical conductivity (EC), and sediment particle size] and the occurrence of microplastics all had significant (P<0.05) effects on the distribution of heavy metal concentrations in sediments. Variation partitioning analysis (VPA) showed that the contribution rates of environmental factors and microplastics to the bioavailability of heavy metals were 37.70% and 0.70% respectively, but the combined effect was 49.60%. We conclude that microplastics in sediments may act as carriers of heavy metals and activate their bioavailability, hence posing a potential threat to the ecological security of estuaries and wetlands.
Keywords: Poyang Lake; coexistence; heavy metals speciation; microplastics; sediments.