Distribution and risks of microplastics and phthalate esters in the transition from inland river systems to estuarine and nearshore regions of the Yellow Sea, China

Abstract

Microplastics (MPs) and phthalate esters (PAEs) are emerging pollutants of significant environmental and health concern. The Yellow Sea, a semi-enclosed marginal sea with dense coastal populations and industrial activities, serves as a critical region for studying MP and PAE pollution due to its ecological sensitivity, role in pollutant transport, and relevance to global marine pollution challenges. The distribution and characteristics of MPs and PAEs in surface water and sediment transitioning from an inland river system to estuarine and nearshore regions of the Yellow Sea in China were investigated. MP concentrations in water samples ranged from 0.89 ± 0.15 to 11.47 ± 1.80 items/L and in sediments from 93.33 ± 23.09 to 653.33 ± 50.33 items/kg dw. The main colors of MPs found in water and sediment samples were white and transparent, with fibers being the predominant shape. The primary size range was 0–0.5 mm, and the main polymer components were rayon and polyethylene. The characteristics of MPs in clams were similar to those in water and sediment, except that their predominant colors were black and blue. The total of six PAEs (Σ₆ PAEs) was detected at concentrations between 0.30 and 1.29 μg/L in water and 25.75–163.61 ng/g in sediments. The concentrations of both pollutants demonstrated a distinct spatial gradient, with the highest levels observed in upstream urban areas, followed by progressively decreasing levels in downstream rural zones, and reaching their minimum concentrations in nearshore regions. Variations in the morphological characteristics (color, shape, and size) and polymer composition of MPs were observed between the aquatic phase and sediment phase along the direction of water flow. A significant correlation was found between MP abundance and Σ6 PAEs across both matrices. Ecological risk assessments revealed substantial risks associated with the presence of these pollutants, particularly in urban areas where contamination peaked. Clams collected from the nearshore regions exhibited MP counts of 1.91 ± 0.47 to 2.49 ± 0.63 items/individual and PAEs from 0.51 to 0.91 μg/g, posing high polymer risk from MPs yet no significant health risk from PAEs for human consumers. This study underscores the transition of MP and PAE pollution from riverine to marine environments, providing valuable insights into the critical sources and potential risks associated with marine MPs and PAEs.