Macro- and microplastic emissions and marine input flux in the Yangtze River Delta, China, from 1990 to 2020

The Yangtze River Delta represents a critical hotspot region for plastic pollution generation, transport, and marine discharge flux within China's coastal waters. To assess the long-term evolution patterns of plastic marine input flux in this region, this study employed a bottom-up emission factor methodology integrated with Geographic Information System (GIS) spatial analysis techniques. We developed high-resolution emission inventories for both macroplastics and microplastics, spanning 1990 to 2020, and coupled them with a comprehensive plastic land-to-sea migration probability model for the Yangtze River Delta region. The results demonstrate that the study area generated cumulative plastic emissions totaling 4.21 × 10¹⁰ kg over the 30 years, exhibiting an average annual growth rate of 2.4 %. Macroplastics constituted 97.8 % of total emissions, while microplastics accounted for 2.2 % but demonstrated a substantially higher growth rate of 11.8 %. Plastic emissions exhibited pronounced inter-provincial disparities and urban agglomeration characteristics, with Jiangsu Province registering the highest total emissions (1.57 × 10¹⁰ kg) and Zhejiang Province displaying the most rapid growth rate (2.9 %). The regional average probability of plastic marine input was determined to be 0.5 %, displaying a distinct "coastal high-inland low" gradient distribution pattern. The southeastern coastal areas of Zhejiang Province exhibited the highest marine input probability at 1.2 %. Over the 1990-2020 period, cumulative plastic marine input flux reached 2.13 × 10⁸ kg, with Zhejiang Province contributing the largest proportion (46.9 %). The marine input flux demonstrated an average annual growth rate of 2.5 %. These results provide a scientific basis for targeted plastic pollution control and marine environmental management in the Yangtze River Delta.