Distributions Of Biogenic Elements, Heavy Metals And Potential Ecological Risk Assessment Of Heavy Metal In Surface Sediments From Coastal Sea Of Guandong Province

The concentration of biogenic elements including biogenic silica(BSi),total organic carbon(TOC),total nitrogen(TN),total phosphorus(TP) and organic matter(OM),and heavy metals such as Hg,Pb,Cu and Zn were determined in surface sediments collected from the coastal sea areas of Guandong province between July 2006 and November 2007,in order to understand the distribution of biogenic elements and heavy metals,and to evaluate the potential ecological risk of heavy metals.The concentration of biogenic elements in sediments from Guangdong coasts were within moderate levels compared with sediments from other coastal areas.The contents of BSi,TOC,TN,TP and OM were in the range of 0.02～0.79%,0.010～0.81%,0.01～0.45%,0.007～0.056%,0.67～24.70%,respectively,with average levels of 0.39%,0.81%,0.21%,0.038%,6.29%.Biogenic elements were lower in west coasts than those in east coasts,except for Liusha Bay.The concentrations of biogenic elements were comparable among three sea areas in east coasts.Based on the TOC/TN ratios,TOC in sediments from most sea areas was mainly aquatic organic carbon, while TOC in Liusha Bay was from terrestrial sources.Biogenic elements showed some seasonal differences.Most of biogenic elements except TP were higher in summer,indicating the higher diatom production and sufficient inputs of surface runoff.The high TP concentration in winter reflected the low regenerate rate of TP at low temperature.The pollution of TOC and TP belonged to ClassⅠsediments,TN belonged to ClassⅡ.However,the concentrations of biogenic elements in some sea areas might produce toxicity effects on benthic organisms.The pollution of heavy metals in Guandong coasts belonged to Trace Contamination.All the five heavy metals were below the standard levels of ClassⅠmarine sediment(Marine sediment quality of People Republic of China,GB 18668-2002).Heavy metals were detected in low concentrations in Shuidong Harbor and Leizhou Bay,and were comparable in other sea areas.The concentrations of Hg,Cd,Pb,Cu and Zn were in the range of 0.005～0.158 mg/kg,0.005～0933 mg/kg,3.02～91.35 mg/kg,0.08～64.68 mg/kg,5.51～199.51 mg/kg,respectively, with average levels of 0.038 mg/kg,0.097 mg/kg,27.61 mg/kg,11.41 mg/kg,53.40 mg/kg,respectively.The concentrations in east coasts were generally higher than those in west coasts,with the highest concentrations recorded in Zhelin Bay-Shantou Harbor.The contents of heavy metals were different between summer and winter, which of Hg and Cd were higher in the summer,and the other three metals were higher in winter.The risk index(RI) of heavy metals indicated that the potential ecological risks of heavy-metals generally belonged to the lever of trace contamination to high contamination.Hailing Bay belonged to extremely high contamination,Liusha Bay and Shuidong Harbor belonged to high Contamination,and Leizhou Bay and Daya Bay belonged to moderate contamination.The individual potential ecological risks (E_r~i) assessment showed that Hg presented the most serious ecological risk,and the next was Cu.