Distribution, Occurrence and Risk Assessment of Mercury and Arsenic in the Supergene Environment of the Yellow River Delta,China

黃河三角洲表生環境中汞和砷的分布、賦存及風險評估

Student thesis: Doctoral Thesis

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Award date25 May 2020

Abstract

Mercury (Hg) and arsenic (As) have received worldwide attention for their acute and chronic toxicity effects on humans and wildlife, bioaccumulation in food chains, and persistence in environments. In this study, a total of 46 soils, 21 surface sediments, a sediment core and 129 individual fish were sampled from the Yellow River Delta (YRD). In the soils and sediments, the Hg and As concentrations were analyzed by atomic fluorescence spectrometry (AFS) to obtain their temporal and spatial distributions, and the Hg and As speciations were determined by the European Community Bureau of Reference (BCR) sequential extraction experiment to provide detailed information of their mobility and bioavailability. In different fish tissues the levels of Hg and Se were determined by atomic fluorescence spectrometry (AFS), the levels of Fe, Al, Mn and Zn were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES), and the levels of Ni, Cr, Cu, Co, Pb and Cd were determined by inductively coupled plasma mass spectroscopy (ICP-MS) to establish adequate understanding of their distribution and interaction effect. Besides, multiple evaluating indices and guidelines were applied to assess the contamination status and human health risk in study area.
The major findings of the present research were as follows: (1) The surface soils were collected from different functional areas in the natural reserve of the YRD, and the results showed that Hg levels in the sites of experimental area were significantly higher than those in the core area and buffer area, which was consistent with the human activity intensities of the three functional areas. However, no significant differences of As levels were observed across different areas. (2) A sediment core, spanning the years 1925 to 2012, was analyzed. The historical distribution trend of Hg and As were very similar. The vertical distributions of Hg and As in the sediment core were found to be consistent with humans industrial production activities and artificial modification of the environment throughout history. (3) The results of the BCR sequential extraction experiment indicated that the most hazardous fraction (the exchangeable fraction) contributed only a small percentage of the total concentrations for both Hg and As, while the fraction with low mobility and bioavailability (the residual fraction) represented the maximum composition. (4) The concentrations of Hg, Se, Fe, Al, Mn, Zn, Ni, Cr, Cu, Co, Pb and Cd in muscle, liver, gill and skin of two broadly distributed commercial fish (redlip mullet and Japanese seabass) in the YRD were analyzed. The results demonstrated that the concentrations of all metals significantly varied among tissues (p < 0.01). The concentration of Hg was found to be relatively high in fish muscle compared to other tissues. However, for other metals, their levels in muscle were found to be the lowest. Besides, the liver and gill displayed higher accumulation ability of all metals except Hg than other tissues. Significant opposite relationships (p < 0.05) were observed between fish size and Mn, Fe, Co, Ni, Cu and Zn in fish muscle. (5) Hg and As levels in all soils and sediments were lower than the maximum toxic limit (WHO, 1989). Some metals (Mn, Fe, Zn and Cd) in fish tissues exceeded the maximum toxic limit proposed by the World Health Organization (WHO, 1989). However, all metals in muscle were well below the limit. Multiple ecological risk indices and guidelines suggested a “good state” regarding Hg and As level in the soils and surface sediments from the YRD. Besides, the toxic effects of all metals were not expected to occur for the consumption of the muscles of the studied fish according to the results of human health risk assessment.

    Research areas

  • Mercury, Arsenic, Supergene environment, Contamination assessment, Risk assessment, Yellow River Delta