Distribution, source and ecological risk of heavy metals in surface seawater of the Southwestern Bohai Strait

This paper is the result of marine and environmental geological survey engineering.

Objective Heavy metal pollution in seawater had long−term adverse effects on the marine ecological environment in the southwest of the Bohai Strait, but the researches focused on evaluation and potential sources of heavy metal pollution were relatively weak.

Methods 43 samples were collected in September and October 2021, and the contents of 6 seawater heavy metals (Cu, Pb, Zn, Cd, Cr, As) were determined. The pollution and risk assessment was carried out by I_geo, Nemero pollution index with weight modification and FQ. The analysis source of heavy metals was explored by correlation analysis and spatial distribution characteristics, and was carried out by PCA and positive matrix factorization (PMF) model.

Results The average mass concentrations of Cr, Cu, Cd, Pb, As and Zn were 0.63 μg/L, 3.09 μg/L, 0.12 μg/L, 0.57 μg/L, 1.30 μg/L and 13.04 μg/L, respectively. The content of Zn element exceeded the average level in the Bohai Sea, and the spatial distribution of heavy metal elements is greatly influenced by aquaculture areas and waterways.The size of the single factor pollution index of seawater heavy metals was arranged in the order of Zn＞Cu＞Pb＞Cd＞As＞Cr. Some sites of Cu, Zn and Pb exceed the standard, and Zn was the most severely. The results of Nemero pollution index with weight modification indicated that the overall quality of seawater were good. The minor stations of mild to moderate pollution which mainly affected by Pb and Zn were distributed in a multi-point pattern west and north of Daheishan island. The results of FQ indicated that Cu and Zn posed high potential ecological risks. The analysis results of the PMF indicated that the sources of heavy metal pollution in the study area mainly included industrial pollution, input of the Yellow River and natural weathering, atmospheric deposition, aquaculture and maritime transportation, with contribution rates of 20.94%, 61.61%, 4.25% and 13.20%, respectively.

Conclusions Industrial pollution and the Yellow River's material input pose significant potential risks to the marine ecological environment in the southwest of the Bohai Strait. The next step is to pay more attention to the trends of Cu and Zn changes in different media and their impact on marine organisms in the study area.