Study On Pollution Characteristics Of Polycyclic Aromatic Hydrocarbons At A Typical Iron And Steel Site In The North

The characteristic of groundwater pollution in the iron and steel industrial fields of China were discussed.The distribution,controlling factors,sources,constitutions,ecological toxicity and migration characteristics of the 16 priority polycyclic aromatic hydrocarbons(PAHs)were analyzed at the field of a typical steel enterprise in the North.The conceptual model of PAHs pollution was built in the typical iron and steel site.The pollution characteristic of groundwater of the iron and steel fields was systematically analyzed by investigating groundwater quality,hydrogeological conditions and production processes of the 5 typical enterprises from different areas in China.BTEX,phenol,petroleum,low molecular weight PAHs,Fe,Mn,Ni and so on are detected more frequently in groundwater due to their higher solubility and migration ability,while the coking plant and the cold rolling plant are the primary sources of groundwater pollution.The operational time and the vertical permeability coefficient of unsatuated zone had the strongest correlation with the groundwater pollution risk index.Leakage from tanks,pipelines and sewage pools,spillage of wastewater and oils,leaching of solid wastes contribute to site pollution together,and the first two ways contributed 48.65 %,48.19% respectively to the total environmental risk values of groundwater.Historically,the steel enterprises were prone to selecting vulnerable areas of groundwater as their sites since hydrological conditions were ignored for accessing water resource.Environmental management,protection measures and vulnerability of unsaturated zone are the controlling factors about protecting groundwater environment of iron and steel sites.71 soil samples were collected from 6 different workshops at a large abandoned iron and steel industrial field.The site was severely contaminated by PAHs and the field could classify three categories based on the average ?PAHs concentrations as follows: >1000 mg/kg(the coking plant),10~1000 mg/kg(the sintering plant,the boiler plant,the iron making plant,the steel making plant),<10 mg/kg(the coal stockyard).The coefficient of variation of individual PAHs exceeded 200 % and the distribution showed strong spatial differences.Wind direction had obviously affected on surface soil of the coking site.Gravel and pebble layer became the preferential flow paths for PAHs,while embedded sand lens existed as the pooling layers and penetrating barriers in unsaturated zone.The ratio of low rings to the total PAHs increased first and then decreased with increasing depth of unsaturated zone in the coking site.Sources were identified by multivariate statistical approach and the ratio method,coal combustion was the primary source of PAHs in the field.Leakage and spillage of coal tar and by-products from deep processing of tar,leaching of coal-like materials lead to that Nap and Phe were the most abundant compounds and 2,3 rings PAHs accounted for more than 25 % of the total PAHs in the chemical product area of the coking plant and the coal stockyard,whereas 4-ring PAHs was the dominant compound in other workshops affected by soot-like materials.The proportion of toxicity equivalency quantity of Bap ranged from 42.5 % to 63.3 % and Bap was most concern about health risk in the iron and steel sites.The ecotoxicity was most serious in the coking site.Soot-like materials and solid wastes mainly enrich in surface soil through dry/wet deposition and rainfall eluviation.Leakage of wastewaters and oils from coking processes containing high concentrations of PAHs and BTEX could cause severe soil pollution,BTEX and other organic contaminates act as co-solvents and competitors in soil adsorption,which could improve migration ability of PAHs and result in pollution in deep unsaturated zone and groundwater.