Soil-Water Interfacial Adsorption/Desorption Behavior Of Phenanthrene In Chinese Zonal Soils With And Without The Addition Of Black Carbon

Polycyclic aromatic hydrocarbons (PAHs) are one kind of hydrophobic organic pollutants in the environment which mainly come from the incomplete combustion of man-made fossil fuel and bio-fuels. Because of its high risk of carcinogenic, teratogenic and mutagenic properties, people pay more attention to the behavior of PAHs in the environment. Many countries have set the PAHs as the testing pollutants for air and soil pollution. Besides, some countries have developed and taken appropriate measures to reduce emissions of PAHs in order to control its pollution. As an important environmental media, soil is responsible for more than 90 percent environmental load of PAHs.Black carbon is a natural adsorbent in the environment. Because of its property of high specific surface area, black carbon can influence the environmental behavior of PAHs and other persistent organic pollutants, such as the transport, degradation and accumulation processes. In order to discuss the influence of black carbon to the environment behavior and the environment effects of organic pollutants, this research selects phenathrene, the representative polycyclic aromatic hydrocarbon, as the experimental object.In this experiment, nine kinds of zonal soils were collected from Hainan (soil 1, soil 2), Fujian (soil 3), Hunan (soil 4), Zhejiang (soil 5), Anhui (soil 6), Jiangsu (soil 7), Liaoning (soil 8), Jilin (soil 9) provinces from southern to northern China. The behavior of adsorption/desorption of phenanthrene in soil-water interface system was studied with and without addition of black carbon to soils. The results are listed as follows.The adsorption capacities of phenanthrene followed the sequence of soil 9> soil 1>soil 2> soil 8> Soil 7> 6 soil> soil 5> Soil 4> soil 3. Simple correlation analysis indicated that the adsorption of phenanthrene by soils was significantly positively related to the organic matter content, but negatively to the content of free ferric oxide and clay particles in soils. Because the sites of soil organic matters to adsorb phenanthrene might be shielded by ferric oxides,, the adsorption of phenanthrene would be reduced with the increase of ferric oxides in soils. The path analysis indicated that the free ferric oxide and organic matter appeared to function in a relatively complex way on phenanthrene adsorption/desorption.Adsorption capacity of phenanthrene was increased with the increase of the addition of black carbon to soils. The adsorption capacity of phenanthrene was mainly controlled by black carbon content and soil organic matter, and the nonlinearity of adsorption became larger after the black carbon was added to soils. The added black carbon, soil free ferric oxide and organic matter are the main factors responsible for the phenanthrene's Koc at low equilibrium concentration level (Ce=0.005Sw), but only the exogenous black carbon is the main factor at high equilibrium concentration level (Ce=0.05Sw,Ce=0.5Sw). The adsorption behavior of phenanthrene would be mainly controlled by black carbon when the content of black carbon is higher than 0.5%.The selected seven zonal soils showed different desorption hysteresis as shown by the hysteresis index (HI) values. The HI value was positively related to the black carbon content and the specific surface area of soils. The presence of black carbon in soil would enhance the adsorption/desorption hysteresis.