Sorption of nitroaromatics to soils: comparison of the importance of soil organic matter versus clay.

Nitroaromatic compounds are produced and used in large quantities worldwide and are frequently detected contaminants in the environment. Sorption is one of the fundamental processes controlling the transport and availability of nitroaromatics, but previous studies have focused mainly on sorption to model clay minerals, whereas little attention has been paid to the sorptive interactions with natural soils. Findings in this study show that soil organic matter (SOM) was the predominant soil component controlling sorption of 2,4-dinitrotoluene and nitrobenzene to three typical Chinese soils, and sorption to clay minerals was much less important. The weak sorption to clay minerals was due to the type of exchangeable cations of the soils, and after saturating the soil clay minerals with K+ and Cs+, sorption to clay minerals increased significantly. Compared with the apolar phenanthrene, 2,4-dinitrotoluene and nitrobenzene exhibited much higher nonhydrophobic affinity to SOM, likely because of the pi-pi electron donor-acceptor interaction between the nitroaromatic molecules and the aromatic structure of the SOM. Moreover, the polarity and aromaticity of SOM might also have important effects on sorption of nitroaromatics. Sorption of nitroaromatics to natural soils appears to be more complicated than sorption of apolar hydrophobic organic compounds, and this complexity should be taken into account in environmental management such as risk calculation and transport modeling.