| Mangrove wetlands are a special ecosystem at the intersection of land and sea.Due to their inherent characteristics,mangrove wetlands can more easily collect pollutants than ordinary tidal flats and can accept a large number of pollutants from rivers,surface runoff and tides;thus,these wetlands are an ideal site for the absorption and storage of many pollutants.Palladium(Pd)in platinum group elements(PGEs)is widely used as a catalyst in vehicle exhaust catalytic converters(VECs).While purifying the exhaust gas,Pd particles are continuously discharged into the environment with the exhaust gas.With the increase of Pd emissions,environmental problems in countries around the world are becoming increasingly serious.In this paper,the mangrove wetland in Dongzhai Harbor,Hainan Province,China,was taken as the research area for the collection of sediment,plant and water samples,taken Pd as the research object.The Pd content was determined by inductively coupled plasma mass spectrometry(ICP-MS).The accumulation characteristics and influencing factors of Pd in sediment,plant and suspended in water were analyzed and discussed.The results showed that:(1)The average Pd content in the sediment was 4.81(1.51?8.15)ng/g,the average Pd content in the plant was 0.94(not detected-4.34)ng/g,and the average Pd content in water particulate matter was 111.44(25.93 to 352.83)ng/g,all of which were higher than the crustal abundance value 0.4 ng/g.Among them,the content level of particulate Pd in water environment was two to three orders of magnitude higher than the crustal abundance value.The particulate Pd content in the water environment of mangrove wetlands was the highest,followed by sediments,and the Pd content in plants was the lowest.(2)The concentrations of granular Pd in sediments,plants and water particle showed a decreasing trend from estuarine to offshore,which the land origin of Pd in the mangrove wetland environment was explained.The concentrations of granular Pd in sediments,plants and water particle showed obvious seasonal changes,and the contents in dry season were significantly higher than that in wet season.Precipitation plays an important role in the seasonal variation of sediment,plant and water particle Pd.(3)In the horizontal dimension,the distribution pattern of sediment Pd content from the mudflat to the mangrove was"V",that is,the highest concentrations were found in the mudflat,the lowest in the forest edge,and the second-highest in the forest.In the vertical direction,the average concentrations of Pd were the highest at the surface at 10-20 cm and decreased with increasing depth.Pd concentrations were significantly positively correlated with pH and negatively correlated with Eh.This finding indicates that pH and Eh have a profound impact on the accumulation and migration of Pd in mangrove wetland sediments.(4)In the horizontal dimension,the Pd content of mangrove leaves from the mudflat to the mangrove direction presents the characteristics of forest>mudflat>forest edge.In the vertical dimension,the concentrations of leaf Pd root decreases upward.Compared with the stem,the content of Pd in leaves were obviously lower.There were age differences in mangrove plants,the concentrations of stem Pd were mature>young>aging,and the concentrations of leaf Pd was old>mature>young.Compared with other studies on plant Pd at home and abroad,the Pd concentrations of mangrove plants in Dongzhai Harbor was relatively lower.(5)The particulate Pd content in the water environment is affected by tidal and rainfall characteristics.The concentrations of water particulate matter Pd at spring tide were higher than those at neap tide.The concentrations of water particulate matter Pd at ebb tide were higher than those at flood tide.The water particulate matter Pd increased after moderate and light rain but decreased after heavy rain.There is a weak correlation between the water particulate matter Pd content in water and pH,Eh,and Cl~-,indicating that it has little effect on the water particulate matter Pd content in water. |
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