Research Of Site Risk Assessment Based On Heavy Metal Pollution Characteristics And Bioavailability

In recent years,with the continuous transformation of modern industrial production technology and the development of urbanization process,a large number of industrial enterprises around the city have been relocated or closed,leaving a large number of contaminated sites.Because of the deficiency of environmental protection awareness and the low technical level,there are circumstances like pollution leakage,waste residue and so on during the production and operation process of industrial enterprises,which can easily pollute soil and groundwater.Heavy metal pollution at these sites have become a nonnegligible environmental problem where risk assessment and soil remediation need to be in progress.Understanding the characteristics of heavy metal pollution in the sites and mastering the changes in the fraction and bioavailability of heavy metals are conducive to identify the site risk more scientifically,design the site remediation plan more reasonably and to some extent to avoid over-remediation sites.In this paper,the distribution of heavy metals in the soil was studied by simulation analysis.The bioavailability of heavy metals in the field was studied by in vitro simulated digestion experiment based on which risk assessment was further conducted.Ultimately,explore feasibility of the heavy metal bioavailability based risk assessment and zoning risk assessment.The main conclusions are as follows:(1)One polluted site was chosen to investigate and found that the site was of serious heavy metal pollution.The main concerned pollutants in soil were chromium,hexavalent chromium,lead,cadmium,zinc,arsenic and the pollution depth was about 4 m.groundwater while the main concerned pollutants in groundwater were lead,hexavalent chromium,zinc,cadmium,arsenic.The soil pollution in the site was relatively serious and the soil pollution was mainly concentrated at 0-3 m while there was a decreasing tendency of pollutants concentrations in the soil from top to bottom.The pollution was mainly distributed in the vicinity of the chromium residue yard and the production workshop of which arsenic,lead,zinc pollution distribution had a greater correlation.Pollutants concentrations of the soil below 4 m did not exceed the standard.(2)The polluted soils were used as the research object and it was found that the heavy metals fractions in the soil were related to the total amounts of heavy metals and the contents of organic matter at the horizontal and vertical levels.There was a significant positive correlation between the bioavailability of chromium,lead and cadmium in the site and their total amounts.With the analysis of heavy metal bioavailability,we found that the bioavailability of chromium and cadmium were positively correlated with the contents of organic matter while the bioavailability of lead was significantly negative correlated with the contents of organic matter.The average bioavailability of chromium,lead,cadmium and arsenic in the site was 20.70%,14.38%,9.36%and 18.53%respectively.According to the organic matter simulation,the site was divided into area A and area B which could effectively reduce the variation coefficient of the bioavailability of the whole site.The maximum bioavailability values between area A and area B were chosen as the bioavailability of the site which could be more scientific and accurate to assess the zoning health risk based on bioavailability.(3)The health risk assessment and environmental risk assessment were carried out according to the pollution characteristics of the site and the repaired target and range were also determined.The results showed that the hexavalent chromium,chromium,cadmium,arsenic and zinc were of health risk.On the basis of the conventional health risk assessment,the feasibility of health risk assessment based on bioavailability of heavy metals and the application of zoning health risk assessment were explored.The results indicated that health risk assessment based on heavy metals bioavailability and zoning health risk assessment could be more scientific and realistic to reflect the site risk than conventional health risk assessment while achieving more accurate site repaired targets and avoiding site over-remediation.