Heavy Metal Pollution Assessment In Longgang Riverat Shenzhen City And The Effect Of Iron Powderon Metals Sediment

The topic of this paper was related to the project of Dongjiang water pollution control and governance at No. 2008ZX07211, which belonged to the national important scientific and technological special projects. The contents of heavy metals in the water and surface sediments, and the speciation, leaching toxicity and bioavailability of heavy metals in surface sediments of Longgang River were studied and the pollution level was evaluated. Besides that, the short-term effect of iron powder on Cu, Ni, Cr and Cr6+ in sediments was also studied in two conditions, in the light or in the dark. The results could provide the basis and guidance for the pollution assessment and sediment dredging of Longgang River.It was got that the concentration of Cr was highest, 2.5-3.5 mg/L, and secondly was Ni, Pb and Cu in water. The contents of Cu and Zn in surface sediments were highest, which were 5.27-1865 mg/kg and 198.4-1275 mg/kg respectively, followed by Cr(54.39- 908.7 mg/kg), Ni(31.3-445.5 mg/kg) and Pb(11.63-814.9 mg/kg), and Hg was only detected in the reach of Xinsheng Village whose content was 0.067 mg/kg. The main forms for heavy metals were residual Cd, Fe/Mn oxidation Cr and residual Cr, organic bound Cu and residual Cu, Fe/Mn oxidation Ni, Pb and Zn. The toxicity leaching percentages of Ni and Cd were generally higher than other heavy metals and the bioavailability leaching percentages of Cr and Ni were relatively higher.The heavy metal pollution in water was evaluated by the national surface water quality standard and the results showed that the concentrations of Pb in the water and pore water samples were high and some were beyond the V-class level. The heavy metal pollution in sediments in Longgang River was comprehensively evaluated by the national marine sediment quality standard, the potential ecological risk index and the accumulation index method. It was got that the pollution of Cu and Cd in surface sediments in Longgang River was the most serious, and that of Hg was the least. The pollution of sediments in the reach of Huiyan high-speed, Ailian Village and Pingxi Village was more serious than that of other sediments.By comparing the results of samples with and without iron powder, it was got that the effect of iron powder on Cu in the sediment was little and the percentage changed was less than 1%. The stability of Cu would be enhanced after adding 2.5% or 5% iron powder in the light, or adding 0.1%, 0.5%, 1.25% or 5% iron powder in the dark. The effect of iron powder on Ni absorption and bioavailability leaching of the sediments was little, but could enhance the stability and reduce the effect of redox condition. The iron powder had an obvious effect on Cr in the sediment. The absorption percentage of Cr was lower than Cu and Ni, and after adding the same iron powder, it became higher in the dark than in the light. In the dark, the more iron powder was added, the less Cr toxicity leaching became. The stability of Cr in the sediment was also enhanced after adding the iron powder. The absorption percentage of Cr6+ in the light was higher than in the dark. And the Cr6+ bioavailability leaching in the dark was more serious than in the light.