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.