Phthalates in sediments and aquatic biota across 30 rivers in Taiwan-long-term background monitoring of the environmental distribution of chemical substances trends, congener shifts, and ecological risks.

Phthalate esters (PAEs) are a class of widely used plasticizers that pose ecological and human-health concerns once released into aquatic environments via industrial, domestic, and agricultural activities. This study provides the first nationwide evaluation of PAE regulation effectiveness in Taiwan, using the national project database for background monitoring of the environmental distribution of chemical substances (BMECs). Concentrations of nine PAE congeners were assessed in 1917 sediment and 678 fish samples collected from 30 major rivers across four regions during 2001-2023. Spatial, seasonal, and temporal trends, congener profiles, ecological risk quotients (RQs), and biota-sediment accumulation factors (BSAFs) were evaluated across seven monitoring stages. PAEs were detected throughout Taiwan's river systems. Sediment ΣPAE concentrations were highest in southern and northern Taiwan, whereas fish burdens were greatest in eastern Taiwan, followed by southern Taiwan. DEHP, DINP, and DIDP were the dominant congeners in both matrices. Sediment concentrations generally increased from upstream to downstream reaches, consistent with cumulative inputs from industrial, urban, wastewater, and commercial sources. In contrast, fish contained higher PAE concentrations at upstream sites, likely reflecting differences in species composition, residence time, body size, and exposure pathways. Sediment concentrations were higher during the dry season, when dilution was reduced. Following strengthened controls after 2011, legacy PAEs declined, while DINP and DIDP increased, indicating substitution. RQs above 1 for DEHP, DINP, and DIDP indicated ecological concern, particularly downstream. High BSAFs in Cyprinidae (25.5) and Lutjanidae (24.9) identified fish groups requiring priority attention. These findings support PAE monitoring, ecological and human health risk assessment, and chemical control and management strategies in Taiwan.