Study On The Risk Assessment For Typical Heavy Metal Contaminated Sites And Remediation Target Values

In this paper, a chromium salt production site is taken as the research object. On the basis of the investigation and analysis of previous production history, raw materials, products, production process and pollution control measures regarding this site, the heavy metal environment quality and characteristics and distributions of site soils are correspondingly analyzed through sampling monitoring. Used the income data on the site in the early expansion to assess ecological risk and health risk, Meanwhile,4pollutants probably harmful to human health are selected as the target pollutants and the remediation targets thereof are respectively calculated. Through the above research, draw the following conclusions:1. The pollution condition of the heavy metals contaminated sitesAccording to the site monitoring data, using the index method to evaluate the levels of pollutants in contaminated sites. According to the monitoring results, the excessive points are judged to be all located in this site. Obviously, this site suffers from severe heavy metal pollution, wherein4pollutants (As, Cr, Cr (VI), and Ni) in the site soil samples exceed the standards, but Cd, Cu and Zn do not. Additionally, chromium pollution is the most severe in the soil and in the meanwhile Cr(VI) monitoring data shows that Cr(VI) in the samples collected from the pollution point locations is an important existing form of Cr in the contaminated soils of the site. Following this, nickel pollution ranks as the second while arsenic pollution ranks as the third.2. The pollution distributionThe key links such as Main production areas of the original enterprise, chrome slag yard and the circulating water pond are heavily polluted region. In the soil samples, most points of monitoring concentration change is consistent with a tendency, which is concentrations decrease with the increase of sampling depth, individual jump points appear. Arsenic and chromium (chromium and Cr (VI)) and nickel contamination showed homology, but also individual level fluctuation. The reason may be due to artificial disturbances caused by surface runoff.3. Ecological risk assessment of the contaminated siteUsing the potential ecological risk index method which created by Sweden scientist Lars Hakanson for ecological risk assessment at the site, results show that, potential ecological risk of heavy metals from a single perspective, Cr has the most ecological hazards, nickel pollution ranks as the second while arsenic pollution ranks as the third. In all of the monitoring samples, copper, zinc and cadmium are minor ecological harm. From the standpoint of total potential ecological risk, ecological risk index generally decreases with the increases of the depth. Samples of the surface layer,0.5m,1m, has the most severe ecological risk.4. Result of health risk assessmentIn the residential land scenario, adults and children are exposure population. On the basis of the behavior characteristics of heavy metal pollutants in soil environment, the main exposure pathways of sensitive population are as follows:oral intake, skin contact and inhalation. After relevant toxicity parameters of pollutants are taken into comprehensive consideration, health risk assessment model is adopted to calculate cancer risk and hazard quotient of site soil pollutants. The results show that, As to carcinogenic risk, the carcinogenic hexavalent chromium are most at risk followed by arsenic, nickel minimum. In the terms of non-carcinogenic risks, arsenic are most at risk, hexavalent chromium pollution ranks as the second while nickel pollution ranks as the third.5. Calculation result of pollution remediation target10-6and1are taken as acceptable risk levels, health risk assessment model is used to calculate the site pollution control target, namely remediation target values:As:0.368mg·kg-1, Cr(Ⅵ):0.251mg·kg-1, Ni:90.6mg·kg-1.