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BACKGROUND The contamination of arsenic and mercury in intertidal sediments will lead to excessive levels of arsenic and mercury in the flora and fauna of the region, which will seriously affect the ecological environment of local vegetation and further affect the survival and safety of human beings. Therefore, it is of great practical significance to study the changes in the contents and spatial distribution of arsenic and mercury in intertidal sediments. OBJECTIVES To investigate the contents of arsenic and mercury in sediments, so as to provide basic information on the pollution of arsenic and mercury in intertidal sediments. METHODS The contents of arsenic and mercury in the sediments of the study area were determined by atomic fluorescence spectrometry (AFS), and iron was selected as the normalized element to establish the environmental background values of arsenic and mercury elements in different intertidal sediments. The geoaccumulation index method and potential ecological hazard index method were used to evaluate the pollution status of arsenic and mercury in the study area. RESULTS Background value of arsenic content: Minjiang Estuary (2.90mg/kg) < Daliao Estuary (6.42mg/kg) < Yancheng Shoal in northern Jiangsu (11.02mg/kg) < Pearl River Estuary (19.19mg/kg). Background value of mercury content: maximum in Pearl River Estuary (0.08mg/kg), less in Daliao Estuary, Yancheng shoal and Minjiang Estuary (0.02mg/kg, 0.02mg/kg, 0.03mg/kg, respectively). The maximum values of background values of arsenic and mercury were both found in the Pearl River Estuary, and the minimum values were located in the Minjiang Estuary. The maximum values of arsenic and mercury of sediments were both found in the Pearl River Estuary, which were 42.90mg/kg and 0.287mg/kg, respectively, and were greater than the first class of Marine Sediment Quality Standard (arsenic: 20.0mg/kg; mercury: 0.2mg/kg). Arsenic belonged to no pollution and slight potential ecological hazards in the four intertidal sediments. Mercury was a medium potential ecological hazard in the Pearl River Estuary, and slight pollution or no pollution in the other three intertidal sediments. CONCLUSIONS The distribution of arsenic and mercury in the sediments of the four intertidal zones in the study area is characterized by "high in the south and low in the north". The arsenic and mercury contents in the intertidal sediments of Minjiang and Pearl River estuaries are more influenced by industrial and agricultural activities, thus causing the distribution features. The pollution of arsenic and mercury in the Pearl River Estuary is more serious than other intertidal areas, so it is urgent to strengthen the control of their pollution trends.

BACKGROUND: The contamination of arsenic and mercury in intertidal sediments will lead to excessive levels of arsenic and mercury in the flora and fauna of the region, which will seriously affect the ecological environment of local vegetation and further affect the survival and safety of human beings. Therefore, it is of great practical significance to study the changes in the contents and spatial distribution of arsenic and mercury in intertidal sediments. OBJECTIVES: To investigate the contents of arsenic and mercury in sediments, so as to provide basic information on the pollution of arsenic and mercury in intertidal sediments. METHODS: The contents of arsenic and mercury in the sediments of the study area were determined by atomic fluorescence spectrometry (AFS), and iron was selected as the normalized element to establish the environmental background values of arsenic and mercury elements in different intertidal sediments. The geoaccumulation index method and potential ecological hazard index method were used to evaluate the pollution status of arsenic and mercury in the study area. RESULTS: Background value of arsenic content: Minjiang Estuary (2. 90mg / kg)

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Concentrations and distribution of n -alkanes ( n -C 14 to n -C 33 ) in Lake Wanghu sediment core were analyzed to investigate the environmental changes in the lake during the past~100 years. Relatively higher concentrations of mid-and long-chain n -alkanes with a strong odd-over-even carbon number predominance indicated organic matter contributions dominated by aquatic macrophytes and terrestrial plants. The lower values of 2 n -C 31 /( n -C 27 + n -C 29 ) highlighted a type of landscape dominated by woody plants. The environmental changes that have been happening over the past 100 years in Lake Wanghu can be divided into three stages, based on the organic matter sources inferred from the changes in n -alkane parameters in the sediments. Before the 1950s, higher values of terrigenous/aquatic ratio (TAR) and high-/low-molecular weight n-alkanes (H/L) indicated vascular, plant-derived sediments deposited during a low-nutrient, clear-water phase with frequent water exchange between the lake and the Yangtze River. Between the 1950s and 1980s, decrease in values of H/L and TAR, and increase in the proportion of mid-and short-chain n -alkanes indicated a shift towards mid-and shorter-chain components likely associated with the increasing contribution of macrophytes and algae. Lower 2 n -C 17 /( n -C 23 + n -C 25 ) values indicated a relatively low algal abundance. In that stage, the lake trophic state increased slightly with the decreasing influence of the Yangtze River flow. After the 1980s,H/L and TAR values increased and then decreased, total n -alkane concentrations and 2 n -C 17 /( n -C 23 + n -C 25 ) increased significantly, especially after 2000s, suggesting the main contributor to high organic matter input most likely shifted to algae because of the eutrophication caused by anthropogenic activities.