Pollution Assesment Of Heavy Metals And Distribution Law Between Heavy Metal Concentration And Particle Size In Jiehe River Sediments

Jiehe river is the mother river of Zhaoyuan city.Jiehe basin is distributed with many industrial enterprises such as gold-smelting,stone processing.Because of the construction-lag of sewage pipe-network and illegal discharge of pollutants in the early years,there were lots of heavy metals entering the river and accumulating in the sediments.With the aim of understanding the heavy metal pollution levels of the sediments,formulating a reasonable dredging way and then restoring the ecological environment of Jiehe river,this study was carried out.In this paper,the pollution of heavy metals in the sediments was evaluated by the method of geoaccumulation index and potential ecological risk index.Then based on the heavy metals,the probability of resource-utilization of the sediments was discussed.The relationship between heavy metal content and particle size was clarified and according to the result,dredged sediment can be sieved to achieve the goal of reducing quantity and resource-utilization.At the same time,with the purpose to figuring out the sources of heavy metal,the main raw materials and process flows of the major industries in the basin were analysed.And then suggestions to the efficient supervision and prevention to heavy metal pollution in the river basin were made.The main conclusions are as follows.(1)The accumulation of heavy metals,especially Cd,in the study area has a quite serious situation.The variation coefficiency of heavy metal is 18%-109%,meaning that the sediments were mainly polluted by the man-made pollution.The polluted elements include Ni,As,Cd,Hg,Pb,Zn and Cu in the study area.According to the geoaccumulation index,point J1 and J3 were in the range of below heavy pollution.Point J2 and J4 were in the range of below moderate pollution.J5 and J6 were in the range of slight pollution.The order of pollution levels of heavy metals was Cd > Zn > Cu > As > Ni > Pb > Hg > Cr.The order of pollution levels of samples was J3 > J1 > J2 > J4 > J6 > J5.According to the comprehensive ecological risk index,J1 and J3 were in high level;J2 point was in moderate level while J4,J5 and J6 were in low level.The order of the ecological risk degree was J3 > J1 > J2 > J6 > J4 > J5.The order of potential ecological risk of heavy metals was Cd > Hg > As > Cu > Ni > Pb > Zn > Cr.According to the limit of heavy metals in standard of resource-utilization such as agricultural use,afforestation in gardens or forests,land improvement,brick making and cement clinker making,J4,J5 and J6 can be directly used for utilization.As the content of Cd was beyond the standard limit,J1 can not be directly used for agriculture,afforestation in gardens or forests,and land improvement.J2 can not be directly used for agriculture as the content of As was beyond the standard limit.J3 also can not be directly used for any resource utilizationts because the As beyond all the standard limits.(2)The sediments in study area were mainly sand.The percentage of the sediments with the particle-size of < 75?m,75-150?m,150-300?m,300-600?m,600-1180?m,1180-2360?m were 2%,2%,9%,20%,39%,28%,respectively.Most of the sediment in the study area were above 150?m,with the percentage of 96%.With the decrease of particle size,the content of heavy metals increased.And the proportion of available state increased.So there was a higher risk of secondary pollution.Meanwhile with the decrease of particle size,the reducible fraction and oxidizible fraction increased,meaning the increasing of organic matter and iron-manganese oxides in smaller sediments,which is the reason the small sediments could adsorb more heavy metals.Take Zn of the sample J1 as an example,the sediments with the size of < 75?m,75-150?m,150-300?m,300-600?m,600-2360?m were 1223.6,665.1,373.5,209.6,119.1mg/kg,respectively.With the decrease of particle size,the percentage of reducible fraction,oxidizable fraction and available fraction increased from 9.9% to 24.7%,12.2% to 22.7% and 70.3% to 87.7%,respectively.According to the limits of heavy metals used for land-utilization and building materials,the sediments with size above 600?m in J1,J2 and J3 can be used for agriculture,and the sediments with size above 75?m in J1 and J2 and size above 150?m in J3 can be used for afforestation in gardens or forests,land improvement,brick and cement clinker making.67%-98% of disposable sediment can be reduced by screening treatment.(3)The main sources of heavy metal pollution in the basin include mine water,waste rock,wastewater,tailings in ore-dressing,wastewater,tailings in gold-smelting,mud in stone industry,dust and ash in tire industry,non-point pollution of agriculture and mine wastewater in rainy season.The pollution elements of heavy metals in mining,ore-dressing industry,and mine wastewater in rainy season are Zn,Cu,Cd,Ni,etc.The major elements of heavy metal pollution in the gold-smelting industry are Zn,As,Cu,Cd,Ni,etc.The major heavy metal pollution elements in the stone industry are Cu,Zn,Pb,Cr,Ni,As,etc.The main heavy metal of pollutionin the tire industry is Zn.The corresponding technical measures and management measures for heavy metal pollution control were suggested according to pollution characteristics in the basin.