## 3 Results and Discussion
### Column Tests  
The results of the batch tests reveal that there is a significant interaction between TNT and aniline adsorption on the loess, and we speculate that the interaction may also exist in  
Figure 2: Effect of aniline on TNT adsorption on Chinese loess. (**a,b**) are for 50.0 and 100.0 mg/L TNT concentrations, respectively. their transportation when they coexist. To identify the hypothesis, two groups of column tests were conducted and the results are shown in Figure 3.  
In the first group tests (Figure 3a), when aniline and TNT exist alone, the breakthrough points of the start and end are 4.5 d and 3.5 d, 7 d and 7 d with the aniline and TNT concentrations of 10.0 mg/L and 100.0 mg/L, respectively. These show that aniline has a smaller mobility than that of TNT, which agrees with the conclusion obtained from the batch tests: that the adsorption capacity of aniline is larger than that of TNT. As a comparison, when aniline and TNT coexist, their start and end breakthrough points are changed to 3.5 d and 2.5 d, 6.5 d and 7 d at 10.0 mg/L and 100.0 mg/L of aniline and TNT, respectively, which also shows that the mobility of aniline is smaller than that of TNT, and the same phenomenon is reported by [PERSON] et al. (2006) [26]. More significantly, compared with the breakthrough points for aniline and TNT existing alone at 10.0 mg/L and 100.0 mg/L, their breakthrough points at the start and end appear ahead, proving that there is indeed interaction between aniline and TNT adsorptions on the loess, and they promote each other to migrate in the saturated loess when they coexist. The ahead-of-breakthrough time is different when aniline is shorter than TNT, and the breakthrough curve of aniline shrinks its opening more obviously than that of TNT, further showing that the influence of aniline on TNT adsorption is more remarkable than that of TNT on aniline adsorption. These results are the same as those obtained from the batch tests, which give a good explanation for our hypothesis. To further prove the significant influence of aniline, initial concentrations with 25.0 mg/L aniline and 50.0 mg/L TNT were conducted, and their breakthrough curves are shown in Figure 3b. When aniline and TNT exist alone, their breakthrough points at the start and end are about 2.5 and 5.0, 5.5 and 9.5 d, respectively. Nevertheless, when aniline and TNT coexist, the breakthrough points are changed to 2.0 d and 2.0 d, 4.0 d and 5.0 d, and the time appears to be ahead, about 0.5 and 3.0, 1.5 and 4.5 d compared with that of their existence alone. Consequently, it is clear that the ahead-of-time for aniline is shorter than that for TNT; meanwhile, the breakthrough curves shrink their openings to 2.0 and 3.0 d for aniline and TNT when they coexist, and the shrink extent is smaller for aniline than for TNT. All this proves that the influences of aniline on TNT adsorption are stronger than those of TNT on aniline, and this is supported by the results of the batch tests study. From the above, the organics of aniline and TNT have different polarities, which determine their diverse mechanisms and performances of adsorption on the loess. And moreover, the organics showed different inhibitions to each other when they coexisted. These inhibition effects are conducive to TNT and aniline preferring the water solution rather than being fixed on loess to enhance their migration in the saturated loess-water system. Therefore, there are interactions for multiple pollutants, and their transport behaviors will inevitably be affected in the combined pollution soil environment [1; 2; 32]. In our present study, aniline and TNT compete to be adsorbed on the loess and then their trans  
Figure 3: TNT and aniline breakthrough curves of column tests under individual and coexisting conditions. (**a**,**b**) are for 10.0 mg/L aniline and 100.0 mg/L TNT, 25.0 mg/L aniline and 50.0 mg/L TNT, respectively. port in the saturated loess is significantly enhanced. Similarly, [PERSON] et al.