## 3 Results
### Effect of Soil Type on the Degradation  
Sterile slurry samples were prepared in this study as references to estimate the contribution of biological degradation separately from adsorption and abiotic reactions in the decrease of the target compounds. The differences in the residual ratios between the sterile and nonsterile samples indicate the contribution of biological degradation. In this study, the term \"degradation\" means degradation at least as parent compounds, because no transformation products were measured. The residual ratios as shown for 14 days in Figure 1 (humic andosol slurry, Ome) were plotted with the results on the sterile  
Figure 1: The residual ratios of pharmaceuticals as parent compounds with elapsed time by humic andosol (Ome) under (**a**) aerobic conditions and (**b**) anaerobic conditions. references in Figure 2. Figures 3-5 shows the residual ratios in slurry samples containing other soils in the same way. As shown in Figures 2-5, higher residual concentrations were observed under anaerobic condition for most of the target compounds. The exception was NPX, which decreased its concentration at higher rates in anaerobic condition. The higher anaerobic degradation rates of NPX, unlike the cases of other NSAIDs, were consistent with previous reports on anaerobic digestion of sewage sludge [5; 13; 24], although transformation products of NPX have usually been detected after aerobic and anaerobic treatment [25; 26]. No anaerobic degradation of CA was observed. Anaerobic condition significantly suppressed the degradation of FEP and KEP, while moderate suppressions were observed for IBP and DCF. On the contrary to the cases in anaerobic condition, the concentration of the target pharmaceuticals decreased with relatively higher rates in aerobic condition. DCF was almost completely disappeared in aerobic slurry regardless of the origins of the soils after 14 days of incubation. The high degradability of DCF in this study was quite different behavior from that in aerobic wastewater treatment where DCF is persistent in general [16; 27; 28; 29; 30]. IBP and FEP were also degraded completely regardless of the origin of soils under aerobic condition, although several metabolites of IBP have been well known in biological degradation [31]. In the case of KEP and NPX, 29-75% of the initial concentrations remained after 14 day of aerobic incubation in the cases of Kawagoe soil (both flooded season and dry season), although the residual concentrations of these compounds were small in the slurry samples containing the other soils, probably because of the difference in the constituents of the soils and the difference in the microbial communities. The degradation of CA was the slowest among the target pharmaceuticals. No obvious aerobic degradation of CA was observed in the soils taken at iris garden and in Kawagoe rice paddy field, reflecting the persistency of CA in biological reactions [6; 32; 30]. Although the reaction rates were small, the soils taken at Ome and Niigata rice paddy fields degraded CA slowly, which is consistent with the reported slow but steady reaction in the soil environments [33]. According to a previous literature [34], the microbial degraders of CA were highly localized into soils exposed to an herbicide propanil, which has a similar chlorinated aromatic ring molecular structure as CA. The difference in microbial community, affected by the history of the applied herbicides, would have influenced the aerobic degradation of CA. As mentioned in the earlier section on the dissolved oxygen concentration after incubation, the microaerobic environment (dissolved concentration of 0.7 mg/L) was unexpectedly provided instead of the anaerobic environment for the surface top soil sample of the iris garden. Only a slight difference in the degradation spectrum was observed between aerobic and microaerobic environments in this soil. Figure 2: Residual ratios of the pharmaceuticals in humic andosol (Ome) slurry after 14 days of incubation under aerobic (**a**) and anaerobic (**b**) conditions.