Baseline levels and spatial distribution of arsenic species in surface sediments of the East China Sea shelf.

To establish a baseline dataset of arsenic speciation in surface sediments of the East China Sea shelf, 87 sampling stations were deployed across the shelf, and concentrations of total As, arsenite (As(III)), arsenate (As(V)), and dimethylarsinic acid (DMA) were determined using high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The results showed that total As concentrations ranged from 3.83 to 36.70 mg/kg dw, with a mean value of 9.46 mg/kg dw, exhibiting an overall spatial pattern of decreasing from nearshore to offshore. As(V) was the dominant arsenic species, accounting for 30.61% of total arsenic; its nearshore high-value zones were more concentrated, and its concentration gradient was steeper than that of total arsenic. As(III) and DMA were present at extremely low concentrations, making up 0.03% and 0.19% of total arsenic, respectively. Cross-regional comparisons show that total arsenic concentrations in the study area fall within the normal range of variation across the eastern Chinese continental shelf. However, nearshore high-value zones are comparable to those in the Yangtze River Estuary and Pearl River Estuary, indicative of pronounced spatial differentiation. As(V) is the dominant inorganic arsenic form in most marine surface sediments, but comparable total arsenic concentrations do not correspond to equivalent toxicity. This finding demonstrates that anthropogenic inputs, rather than geological background, serve as the dominant factor governing the ecological toxicity of sedimentary arsenic. This study provides critical baseline data for the environmental quality assessment and biogeochemical cycle research of arsenic in the East China Sea shelf.