| Based on the results of ecological geochemical survey and 160 crop samples in the Pearl River Delta Economic Zone,this paper evaluates the possible risks of heavy metals in the Pearl River delta soil by using four different evaluation models.The evaluation were conducted from three different angles:the total amount of heavy metals,heavy metal activity and crop safety.In addition,the spatial distribution characteristics of risks caused by heavy metals in the region were characterized by GIS.The total results of environment risk assessment and human health risk assessment show that As?Cd?Cu and Hg elements in the topsoil are the primary heavy metals posing risks to the Pearl River Delta while the risks coming from Cr and Zn elements are negligible.Meanwhile,23.89%of soil samples have a hazard index of more than1,which suggests that it is likely to cause chronic diseases.The soils with high hazard index are mainly distributed in the Quaternary area.37.22%of soil samples have a negligible chronic risk level,of which the spatial distribution is relatively consistent with granite area.Moreover,the spatial distribution of carcinogenic risk is similar to chronic risk,where the cancer risk index of 25.68%of samples exceed1×10-4,which is recommended by USEPA.Furthermore,the human health risk zoning evaluation results presented at administrative units indicate that there are higher risks in both Panyu and Nansha districts where more attentions should be paid to.The prediction model established based on the activity of Cd and Pb elements in the Pearl River Delta.The results showed that there is a relatively high ecological risk in the Pearl River Delta Quaternary formations,especially the surrounding soils along the west river and east river as well as other pearl river systems.83.85%of the soil in the study area has little ecological risk,while 5.93%of the soil heavy metals are potentially at risk.7.11%of the soil heavy metals are at a high risk which are very sensitive to the environment conditions,and may have caused harmful influences to the environment.The results of the risk zoning of heavy metals in the study area show that 23 of the 42 districts and counties in the Pearl River Delta are safe,and the heavy metals in the soil are not at risk while 11 districts are low risk areas.There are 5medium risk areas,including Haizhu district,Yuexiu district,Chancheng district,Nansha district and Zhongshan district.Areas such as Liwan district,Jianghai district and Shunde district are with the highest risk so that further researches and preventive measures should be taken.Establish the prediction model based on crop safety to evaluate the ecological risks of Cd element in the soil.The results showed that most of the crops planted in the study area were safe,and only a small amount?0.55%?of crops with the Cd content exceeding the food limit level,which suggests the Cd element in these areas have shown ecological risks.The risks are mainly in the Quaternary areas especially near the Pearl River system,and this is consistent with the results of activity-based risk assessment.This paper aims to provide an example for regional ecological risk assessment of soil heavy metals,and to provide scientific basis for land risk management and zoning of the Pearl River Delta. |
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