Characterization of compound pollution and risk assessment of typical pollutants at a coking site

A coking plant in Shanxi was used as the research site. The pollution situation at the plant was determined using on-site monitoring and multiple data analysis methods. The vertical distribution and combined pollution characteristics of typical pollutants were revealed. The horizontal and combined pollution characteristics of typical pollutants were clarified. The health risk assessment model (RAG-C) was used to determine the risk of typical pollutants at the plant to the exposed population. The results are presented below: (1) The soil at this coking plant was severely contaminated. The principal pollutants were benzene series and polycyclic aromatic hydrocarbons, with benzene and naphthalene exhibiting the highest exceedance multiples, at 1109 and 631, respectively. A correlation coefficient was calculated between different pollutants to ascertain the extent of the pollution. The result indicated that the plant was seriously polluted by combining the same pollutant group. A combination of different groups of pollutants was observed. A significant correlation was observed between benzene and naphthalene at the 95% confidence level. Eight sections exhibited simultaneous exceedances of benzene and naphthalene. The highest naphthalene contamination was observed in the -3 m layer of silty soil, while the highest benzene contamination was observed in the -8 m layer of silty soil. The distribution of benzene and naphthalene in the soil was significantly influenced by the lithology of the soil layer and the physicochemical properties of the pollution. Benzene and naphthalene combined pollution was present at different depths. (2) The horizontal distribution of benzene and naphthalene combined pollution was characterized by clear enrichment. It was centered around the crude benzene area, benzene storage area, cold drum area, and tar processing area. Among them, crude benzene and tar processing areas were the main combined pollution areas. The saturated zone contributes to the lateral diffusion of the pollutants. It was assumed that the pollution mainly originated from waste liquid spillage and seepage. From the distribution characteristics of benzene and naphthalene in the soil layers at different depths, there were two major sources of pollution in the tar processing area and the crude benzene section of the site. This was a combined source of benzene and naphthalene. (3) The cancer risks for benzene and naphthalene were 2.47×10−6 and 1.50×10−4, respectively, which exceeded acceptable levels. The site should be classified as an unacceptable risk area that is seriously polluted. The spatial distribution of benzene and naphthalene cancer risk was mainly influenced by the source of pollution. The main exposure pathway was the inhalation of gaseous pollutants in indoor air from the subsoil pathway. Cutting off the volatilization pathway of benzene and naphthalene from the subsoil to the surface air is an effective way to reduce the risks of benzene and naphthalene.