Soil And Crops Heavy Metal Pollution And Potential Health Risk Assessment For The Residents Around Small-scale Polymetallic Mine

Small-scale mining activities and even abandoned could cause serious heavy metal pollution to the surrounding areas,which ultimately threatened the health of local populations.Although metal ore mining activities are well known as an important source of heavy metal pollution to the surrounding soil,the soil heavy metal pollution caused by small-scale mining activities has long been neglected.The study area,which including the small-scale abandoned mine and surrounding three villages,were located in the remote mountainous region of Shaoguan in Guangdong province of south China.This study comprehensively analyzed the impact of mining activities and after abandoned to the heavy metals content of the surrounding soils,the rice and vegetables grown on the soils,and the health risk for the residents living in the villages around the mining district exposure to heavy metals through multiple pathways.This study is of great significance for understanding the small-scale abandoned mine imposed heavy metal pollution in the surrounding environment and health risk for the residents living around the small-scale abandoned mine.The Yaoposhan mine is located on the top of a remote mountainous area in Dabu Town,Ruyuan County,Shaoguan of Guangdong Province.This area has a good environment and with good vegetation coverage.However,due to the opencast mining activities in the Yaoposhan mine area,the mountain is severely stripped,and the ore body is exposed on the surface,and large amounts of tailings are dumped on the hillside without any effective protective measures.In August 2015 to May 2018,we collected 13 tailing samples,3 acid mine drainage,3 source stream water samples in the mining area,23 water samples in the stream flow through the farmlands,10 tap water samples in the households of the villages around the Yaoposhan mine,312 soil samples in the 3 villages,and 122 rice samples and 202 vegetables samples grown on the farmlands around the mine.In addition,we also collected 8 tap water samples,10soil samples,10 rice samples and 52 vegetable samples in the reference village which is obviously not impacted by the mining activities.The contents of Cr,Ni,Cu,Zn,As,Cd,Pb and Hg in all the tailing,water,soil,rice and vegetable samples were determined.Due to the health risk caused by As in the food is mainly attributed to inorganic As?i-As?,for the more accurate health risk assessment of the residents,we analyzed the content of i-As in the rice and vegetable samples consumed by the villagers in the 3village surrounding the Yaoposhan mine.Furthermore,we also taken the bioavailability of heavy metals in the multiple exposure pathways into consideration.The uncertainty of various major parameters were considered in the health risk assessment,including the body weight of the residents,daily intake of the drinking water,rice and vegetables,and the content of i-As in rice and vegetables,and the bioavailability of As,Cd and Pb in multiple exposure routes,as well as the reference dose of each element daily intake and carcinogenic factors.Based on the above results,the heavy metal pollution status of the soil around the mining district and source apportionment of heavy metals in the soil were studied.Meanwhile,the level of heavy metal pollution in stream water,tap water,rice and vegetable were also analyzed.And then the Monte Carlo simulations were used to calculate the non-carcinogenic and carcinogenic risk for the adult residents living around the mine exposure to heavy metals through drinking tap water,consuming local produced rice and vegetables,and by accidental oral ingestion,dermal contact and inhalation of soil particles.In this study,a new method for the rapid and reliable determination of heavy metals in soil by energy dispersive X-ray fluorescence spectrometry?ED-XRF?was conducted,based on the 1029 soil samples which including 709 soil samples collected in the city of Handan in north China and the city of Yingtan in south China,and 320soils samples collected in the farmland soils around the Yaoposhan mine.All soil samples were digested with strong acid and then the heavy metals content determined by ICP-MS were set as a relatively accurate data for reference.Then,the heavy metals content in the corresponding soil sample measured by ED-XRF was then compared with the value determined by ICP-MS to identify the reliability of ED-XRF for determining the heavy metals content in the soil.The main conclusions obtained in this dissertation were listed as follows:?1?As an important source of heavy metal pollution in the surrounding farmland soil,the content of heavy metals in mine tailings and acid mine drainage in the mining district should be understood first.The mean contents of Cr,Ni,Cu,Zn,As,Cd,Pb and Hg in tailings are 117,78.2,2484,2869,440,26.4,3168 and 0.122 mg/kg,respectively.The high contents of Cu,Zn,As,Cd and Pb in tailings is the potential source of these elements in the farmland soils around the mining area.The pH of acid wastewater was ranged from 2.5 to 3.4,in which the mean contents of Cu,Zn,Cd and Pb were 16.0,24.8,0.648 and 2.09 mg/L,respectively.The pH of the source stream water samples in the mining area was ranged from 4.1 to 4.3,which also contained high content of Cu,Zn and Cd,with the average concentrations of 2.69,8.11 and 0.649 mg/L,respectively.These above results show that the mining area is an important source of heavy metals in the soil of surrounding farmlands.After heavy rainfall events,a large amount of heavy metals will migrate to the surrounding soil through surface runoff and subsurface percolation.?2?According to the topography,Chashan Village is located on the back side of the mining area,and the soil heavy metal pollution in this village was lighter,while Xuwu Village and Wulian Village are located under the hillside where the tailings are piled up,so the soil heavy metal pollution is these two villages were more serious,especially in Wulian Village.The soil in the 3 villages around the mining district were suffered moderately to severely heavy metal pollution.The pH of the stream water samples flowing through the farmlands which originated from the mining area were ranged from 6.7 to 7.6,and the mean content of Cd was 15.9?g/L,which exceeds the national standard for surface water environmental quality of grade V?10?g/L?,indicating that it is no longer suitable for farmland irrigation.However,the farmlands around the mining district have long been irrigated by this stream water.The geometric mean contents of Cu,Zn,As,Cd and Pb in the farmland soil of Wulian village were 164,411,89.3,1.85 and 595 mg/kg,respectively,which were far higher than the national soil quality safety standards of 50,200,30,0.3 and 70 mg/kg.And the geometric mean content of As in the farmland soil of the reference village also exceeded80 mg/kg.Based on the results of Pearson correlation and principal component analysis of heavy metals content in the farmlands around the mining area,they show that the area were naturally had high geochemical background values of heavy metals?e.g.As and Cd?,while mining activities had intensified the soil heavy metal pollution,mainly Cu,Zn,As,Cd and Pb.The contents of Cr,Ni and Hg in the soil in this area were within the safe limits.?3?The content of heavy metals in the tap water samples of three villages around the Yaoposhan mine and reference village were far below the corresponding standards for drinking water issued by the National Health Commission of China.The locally grown rice was contaminated by As,Cd and Pb to varying degrees.Especially in the village of Wulian,where the soil was the most heavily polluted by heavy metals,the geometric mean contents of Cd and Pb in rice were 0.603 and 0.386 mg/kg,respectively,which were about 3 and 2 times higher than the corresponding national food safety standards?the limits of Cd and Pb in rice are all 0.2 mg/kg?.The contents of heavy metals in vegetables were generally low,only the content of Pb in some leafy vegetables exceeds the national food safety limit.The content of heavy metals in leafy vegetables was higher than that in non-leaf vegetables.The heavy metals contents in rice and vegetables grown in the farmlands around the mining district were higher than that in the reference village.This shows that heavy metal pollution in soil caused by mining activities will further result in the increase of heavy metals contents of crops planted on it.The species of As in rice and vegetables were dominated by i-As,and the proportions of i-As to total As in rice and vegetable were 82.2%?45.4-100%?and 94.7%?65.2-100%?,respectively.According to the results of i-As and the total As contents in the local grown rice,it can be estimated that about 13%of the rice planted in the farmlands around the Yaoposhan mine had an As content exceeding the national food safety standard limit?0.2 mg/kg?.The rice consumed by residents in Chashan village is purchased from the market in Dabu town and also had relatively high levels of As,although it might not affect by mining activities.This could be attributed to the high As accumulation potential of rice.?4?Residents around the Yaoposhan mine exposed to heavy metals were mainly through the pathways of drinking tap water,consuming locally produced rice and vegetables and by occasional oral ingestion,skin contact and inhalation of fine soil particles.Based on the above results and considering the uncertainty of various parameters,Monte Carlo simulation was used to calculate the non-carcinogenic and carcinogenic health risk for the adult residents living around the mining area exposed to heavy metals through the above routes.The results of health risk assessment show that adult residents living around the Yaoposhan mine suffered significant non-carcinogenic risk,which was mainly caused by uptake of i-As and Cd through rice and vegetable consumption.Exposure to heavy metals through drinking tap water and exposure to soils through three pathways poses no non-carcinogenic risk.The contribution ratios of exposure to heavy metals through the media of rice,vegetable,soil,and tap water for the non-carcinogenic risk of the residents living in the vicinity of the mining district were 62.3-86.6%,8.51-32.9%,2.37-5.03%,and 0.67-1.97%,respectively.The carcinogenic risk for the adult resident exposure to Pb through various pathways was less than 1×10^-4,which was within the acceptable level.The carcinogenic risk to residents was mainly caused by i-As in rice and vegetables,especially in rice.The ILCR for the residents of Wulian village through rice consumption was ranged from 1.7×10^-4 to 1.4×10^-2.Residents around the mining district were at risk of severe bladder and lung cancer and skin cancer through exposure to i-As due to consumption of locally produced rice and vegetables.?5?The result of comparison between the ED-XRF method and ICP-MS for determining the content of heavy metals in the soil shows that the content of Cr in the soil determined by ED-XRF had a large deviation.The linear relationships between the contents of Ni,Cu,Zn,As,Cd and Pb in the soil determined by the ED-XRF and the results of ICP-MS were y=0.68x+12?R²=0.56?,y=0.91x+5.9?R²=0.95?,y=1.01x+4.6?R²=0.90?,y=1.15x+1.4?R²=0.89?,y=0.62x+0.005?R²=0.88?and y=0.97x+2.3?R²=0.92?,respectively.The above results show that the ED-XRF could obtain good results in the determination of heavy metals contents in the soil,especially Cu,Zn,As and Pb,while Ni was 30%lower,and Cd was about 40%lower.In general,this method can relatively quickly and accurately determine the contents of heavy metals in soil.It saves time for the determination of heavy metals in a large number of soil samples,and does not cause secondary pollution to the environment caused by the using of strong acids.The tested soil samples can also be recycled for other tests.