Lam Tin Smelter Surrounding Farmland Soil And Wheat Grain Heavy Metal Pollution Analysis And Evaluation

In recent years,the peripheral soil and crops' heavy metal pollution phenomenon caused by the mining and metallurgy activities was getting more and more serious.The Lantian Smelter was located in the Chen-gou-an village in Lantian County;this factory has been engaged in the production of crude lead more than ten remaining years of life,whose annual crude production of lead was around 2000t.In the production process,a lot of mist and dust including heavy metal and so on lead,zinc was discharged to the air by the point source form,the atmospheric dust fall has polluted the periphery environment seriously massively,and particularly the leeward peripheral farmland soil of this factory.The childhood lead poisoning event was exposed twice in this village around Lantian smelter.To understanding the peripheral soil and crops' heavy metal pollution phenomenon caused by the crude lead smelting activities,based on the analysis,investigation and sampling in the field,the spatial distribution characteristics of the heavy metals contents in wheat seeds and farm land soils and the heavy metal fractionation in farm land soils around the LanTian smelter were studied,the heavy metal pollution level was evaluated with pollution index method, and human health risk assessment caused by the surface soil and wheat grain heavy metal pollution was further to made.The results showed that:(1) In the horizontal direction,the contents of these four heavy metals in the leeward topsoil first arisen,then declined,and finally tended to steady with the increasing distance between sampling spot and smelter.The region in the range of 50～200 meters from smelter was contaminated most seriously by Pb,Zn,Cu and Cd.While the variation of Cr was special showing the trend of arising first,then declining,and increasing to the max in 700 meters distance apart from smelter.However,the content of Ni increased in volatility that the farther away from the smelter,the higher the content,and its change ranges display generally to be small.According to the national soil environment quality secondary standard(level 2),the Pb pollution scope was 0～400m apart from smelter,Cu and Cd have surpassed the national secondary standard in the entire research area,but the contents of Zn,Cr and Ni were lower than the national soil environment quality secondary standard(level 2) value,not so as to constitute the pollution yet.In addition,different heavy metals were dissimilar in different fraction forms in surface layer soil.Among them,Pb was dominantly associated with reducible fraction,Cu was primarily associated with the residual fraction with a mean of 74.62,and the dominant fractions of Zn were reducible fraction and residual fraction,while more than 72%of Cd was associated with reducible and residual fraction. (2) In the vertical direction,the heavy metals mainly concentrate in the surface layer soil. Heavy metal contents decreased with soil depth,and it decreased significantly in the layers of 0～30 cm,while changed smoothly under 30cm soil layers.And the content of Pb and Cd had the similar variation that roughly decreases progressively slowly first,the latter fast drop,then drops slowly again,finally basically tends to be sTable.But the content of Cu and Zn had the similar Variation that roughly decreases progressively fast first,then drops slowly,finally basically tends to be stable.However,the content of Cr and Ni had the special distribution respectively,that rapid decreasing first,then increasing progressively from the surface layer to in-depth.According to the national soil environment quality secondary standard(level 2),the Pb pollution mainly exists in the 0～10cm surface layer soil,the Cu pollution scope is 0～15cm,but Cd pollution ran through the entire profile.However,the contents of Zn,Cr and Ni have not exceeded the allowed figure in the entire profile,so they belonged to the clean elements.(3) In regard to the Index of Geo-accumulation(I_geo)in study area,the main pollution factors are Pb and Cd for all the sampling spot in topsoil and profile soil,Zn and Cu are the secondary pollution factors,however,Cr and Ni belong to the clean element.In the horizontal direction,the Index of Geo-accumulation(I_geo) is different along with distance apart from the smelter among of different heavy metals.The region in the range of 400 meters apart from smelter was contaminated most seriously,and the soil was contaminated moderately to strongly even to extremely with Pb and Cd. In the vertical direction,the heavy mental comprehensive pollution degree is various along with the different depth of the soil layers,and the pollution mainly concentrates in the 20cm above surface layer soil.(4) In the wheat grain's heavy metal content on the whole is basically consistent with the soil in rule,simultaneously also influenced by the heavy metal type and the existence shape.In all wheat grain samples,the content of Pb in wheat seeds was all 100%higher than the China National Hygienic Standards for Food,and Cu,Zn and Cd were 44%,33%,56%respectively.As far as the single factor pollution index concerned,Pb and Cd were main pollution factors,the pollution indices of which are higher than that of Cu and Zn.In regard to combined pollution index,the pollution level of the wheat seeds vary from one monitoring spot to another,which is mainly related to variation of the distance of the monitoring spots from the pollution source.The absorption and concentration ability of wheat grain to the heavy metal varied from different heavy metals,which were in the order of Zn＞Cu＞Cd＞Pb in study area.(5) Based on the Assessment of Health Risk for the surface layer soil and the wheat grain heavy metal pollution,it can be found that the adult and child's health risk size caused by heavy metal Pb, Zn,Cu and Cd is in turn:Pb>>Cd>Cu>Zn.In this area the health risk soil's heavy metal to the local resident was small;the annual mean individual risk index by far was smaller than 1.But comparing with the adult,child's average individual risk index was one time higher of that.Speaking of the sole element which was taken in only through the edible wheat,the THQ of Pb,Zn,Cd for adult were higher than 1,while was still 0.94 slightly lower than 1 for Cu.But child's health risk index was far higher than 1 and was 2 times that of adults.However,for the many kinds of heavy metal's compound pollution,the adult and child's THQ_T was 4.90,13.95 respectively,this indicated that there was big health risk to the human body to eat the wheat produced in this area,and Children were more easily affected by soil and wheat heavy metals.