Layered Health Risk Assessment And Application Study Of A Contaminated Industrial Chemical Plant In Henan Province

With development of cities and upgrade of economic structure,a large number of industrial enterprises in cities collapsed and moved out.As a result,legacy sites have become land resources for the urban construction.Due to historical reasons,some legacy sites were polluted in different levels,and it is necessary to carry out human health risk assessment before further development.At present,the human health risk assessment of contaminated sites in China is still in its infancy.Conventional health risk assessment takes the comprehensive risk of cancer and non-cancer caused by pollutants in all exposure pathways into consideration,but ignores that the depth change of different stratum has different influence on its status of health risk.Therefore,its evaluation result is conservative,and subsequently it will increase the cost of soil remediation and lead to excessive remediation.This study based on the horizontal hydraulic conductivity of a chemical plant in Henan province divides the soil layer into three.Considering the interpolation distribution characteristics of cadmium,arsenic and volatile organic compounds in the site,we adopted layered human health risk assessment method for evaluating them.The results are as follows:The inverse distance weight method(IDW)is used to interpolate the pollutant distribution in the site.The interpolation results show that the high concentration distribution areas of arsenic are in the first layer of the D-acid storage tank and the wastewater treatment station;distribution of cadmium are in the loading and unloading areas of the first layer;distribution of naphthalene are in the second layer of D acid tank area,waste water treatment station and waste depot.Pollutant is composed by traces of material generated in the process of production and storage,as well as leakage from industrial waste-water.The result of layered human health risk assessment indicates that arsenic,cadmium and naphthalene contamination in the first layer is heavier.Thus,the risk of cancer and non-cancer caused by arsenic and cadmium in the first layer exceeds the limit of 10-6 and 1 respectively;cancer risk of naphthalene is greater than that of the limit,and non-cancer risk of it is slightly less than 1.In the second and third layers,only naphthalene has health risks,and the risk is significantly reduced with the depth.The objective value of the layered soil remediation of naphthalene is increased by the depth of stratum.Compared with the results of conventional health risk assessment,the scope of pollution caused by naphthalene and soil volume which required to be remedied is reduced 7468.70 ㎡ and 16075.08m3.For the reasons of the physical and chemical properties of arsenic and cadmium,the soil remediation target value does not varied with the depth,and the value of remediation target could only be calculated in the first layer(Miscellaneous landfill).The layered health risk assessment is applied to polluting sites with volatile pollutants,but does not suitable for sites contaminated by heavy metals.Compared with the results of conventional health risk assessment,layered health risk assessment takes the influence of depth change of the strata on health risks into consideration,under the control of risk.The evaluation results can be referenced by the follow-up contaminated site remediation for choosing the technical scheme,because this scheme strengthens the repair effect and cuts down the cost of restoration.In conclusion,layered health risk assessment provides a reference and guidance for the similar contaminated sites in the future.