Soil heavy metal pollution characteristics, sources and risk assessment in the Yellow River Estuary Delta region

This paper is the result of environmental geological survey engineering.

Objective The Yellow River Delta is the largest and youngest estuarine wetland in China, hosting one of the world's most fragile and youngest wetland ecosystems. Understanding the characteristics and sources of heavy metal pollution in this region is crucial for ecological protection and pollution control.

Methods In May–June 2022, 400 surface soil samples of 0−20 cm soil depth were collected from this region, and concentrations of eight heavy metals, including Zn, Cr, Ni, Cu, Pb, As, Cd and Hg, were measured. Pollutions sources were idientified by the correlation analysis and principal component analysis. Pollution levels were evaluated by using methods, including the single−factor pollution index (Pi), Nemerow composite pollution index (PN), and geo-accumulation index (I_geo). Human health risk assessment methods were applied to evaluate potential risks.

Results (1) In the research sites soil pH was 8.46. The concentrations of Zn, Cr, Ni, Cu, Pb, As, Cd and Hg were 72.38 mg/kg, 71.33 mg/kg, 32.44 mg/kg, 26.12 mg/kg, 17.94 mg/kg, 12.2 mg/kg, 0.14 mg/kg, and 0.03 mg/kg, respectively. (2) Both the single-factor pollution index and geo-accumulation index indicated that the overall soil pollution level was within the mild range. (3) Health risk assessment revealed that oral ingestion was the primary pathway for non-carcinogenic and carcinogenic risks. Children faced higher non-carcinogenic risks than adults, while all samples exhibited carcinogenic risk indices below 10⁻⁴.

Conclusions The soil heavy metal pollution in the Yellow River Delta is relatively low, posing minimal ecological risks.