# Absorption-Translocation of Veterinary Antibiotics in Rice Plants Introduced with Irrigation Water
## 3 Results and Discussion
### Absorption-Translocation and Bioconcentration of VAs into Rice Plants  
Our report found that AMX was evident in stems, roots, and grains (Figure 3). AMX was not detected in rice roots, stems, and brown rice at the ten-fold background level. However, it was detected in stems after six split-dose treatment. At the fifty-fold background level, AMX was absorbed and translocated into the roots and stems regardless of treatment frequency, except in stems with two split-dose and four split-dose treatments. The detected concentration ranged from 19.2 \(\pm\) 0.9 to 79.3 \(\pm\) 0.9 \(\upmu\)g kg\({}^{-1}\). Likewise, AMX was not detected in the stems and roots at the ten-fold background level, although trace concentrations were detected in the stems and roots prior to the harvest stage. Additionally, AMX was also not detected in brown rice treated at the ten-fold background level. Figure 2: Concentrations of amoxicillin, chlorotetracycline residues in soils of the rice fields treated with VAs. The bars represent the standard error; A-1, A-2, A-3, B-1, B-2, B-3, C-1, C-2, and C-3 are described in Table 2.  
CTC absorption into stems, roots, and brown rice is exhibited in Figure 4. CTC was identified in rice roots and stems in all treatment groups, regardless of treatment concentration, frequency, or crop growth stage. However, at the background level, CTC was not detected in brown rice in the groups that received two split-dose or four split-dose treatments. The highest detected concentration of CTC in brown rice was 25.1 \(\pm\) 0.4 \(\upmu\)g kg\({}^{-1}\) when treated with VAs at the fifty-fold background level with a six split-dose treatment. OTC absorption was detected in the stems, roots, and brown rice (Figure 5). OTC displayed a substantially comparable absorption transition pattern to CTC. Overall, this experiment demonstrated that VA accumulation was directly proportional to VA treatment concentration, which is consistent with other research conducted under hydroponic conditions [31; 32]. More frequent application of VAs into the water showed better uptake and translocation into the plant parts as compared with a less regular supply. Under a less regular supply, the water-soluble VAs were efficiently degraded at outdoor temperature and light [33] or runoff with groundwater [34; 35]. VAs belonging to the same antibiotic class had similar absorption-transposition patterns owing to similar solubility, affinity, and absorption mechanisms [36]. Earlier studies suggest that VAs accumulate in the roots in higher concentrations [37]. The octanol/water division of antibiotics is closely related to the translocation of antibiotic uptake into plants (log K\({}_{\text{ow}}\)). CTC and OTC, non-ionized compounds with log K\({}_{\text{ow}}\) values less than 0, were able to move into both the xylem and phloem. The concentrations of CTC and OTC detected in the stems were 4 and 10 times higher than those in the brown rice (Figures 4 and 5). Figure 4: Concentrations (\(\upmu\)g kg\({}^{-1}\)) of chlortetracycline (CTC) detected in the roots, stems, and brown rice of rice plants grown in the experimental plots. The bars represent the standard error. A-1, A-2, A-3, B-1, B-2, B-3, C-1, C-2, and C-3 are described in Table 2.  
Figure 3: Concentration of amoxicillin (AMX) detected in the roots, stems, and brown rice of rice plants grown in the experimental plots. The bars represent the standard error. A-1, A-2, A-3, B-1, B-2, B-3, C-1, C-2, and C-3 are described in Table 2.  
AMX (0 \(<\) log K\({}_{\rm{ow}}\)\(<\) 3) did not translocate into the brown rice at the ten-fold background level. AMX was detected in brown rice when treated with the fifty-fold background level (Figure 3). The continual introduction of VAs into soil, through repeated manure application, may eventually build up their concentration high enough to enter the terrestrial environment as a potent threat [3]. [PERSON] et al. [38] determined whether or not plants grown in manure-applied soil absorb VAs present in manure.