## 3 Results and Discussion  
### Soil Properties and As Concentrations  
The average As concentration in the paddy soil (Table 3) was 23.49 mg/kg, higher than that in the non-karst area of Guangxi (12.01 mg/kg) [49]. The concentrations ranged from 2.36 to 162.92 mg/kg. Arsenic had a high degree of variability, as evidenced by its coefficient of variation (CV % = (standard deviation/mean) \(\times\) 100%) of 98.32% (\(>\)35%) [27]. The paddy soil's As content was greater than the background values of Guangxi (8.0 mg/kg) and the rest of the country (9.0 mg/kg) [50]. Moreover, compared with the published data on the As content in other regions and countries, the mean value of the paddy soil's As content in our study area was higher (Table 4). The median value of As in the study area was close to that in Hunan Province, China, and lower than that in French soils. However, the minimum values of As in Shanghai and Fujian, China, were greater than those in the study area (Table 4). Overall, the paddy soils formed by carbonate rocks had a high level of As enrichment, resulting in a higher geochemical background. [PERSON] et al. [51] confirmed that Pleistocene carbonate-rich terrace deposits, pouri, are the cause of the elevated As concentrations. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Region/Country** & **N** & **Min** & **Max** & **Mean** & **Median** & **References** \\ \hline  & Hunan, China & 18,773 & 0.1 & 2670.1 & 19.5 & 13.0 & [50] \\  & Jiangxi, China & 15,547 & 0.4 & 19.2 & 8.4 & 8.0 & \\  & Jilin, China & 23,465 & 0.4 & 15.9 & 8.0 & 7.9 & \\ Topsoil & Shanghai, China & 1744 & 4.6 & 11.4 & 7.9 & 7.9 & \\ (mg/kg) & Fujian, China & 14,682 & 4.7 & 3.9 & 0.1 & 13.5 & \\  & France & 2017 & 0.39 & 412.00 & 12.20 & 17.93 & \\  & Italy & 201 & 1.8 & 60 & 20 & \(\backslash\) & \\  & Cyprus & 260 & 0.2 & 22.5 & 11.0 & 10.87 & [51; 54] \\ \hline \hline \end{tabular}  
\end{table} 
Table 4: Arsenic concentration in the topsoil and rice from other regions/countries. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Statistics** & **Min** & **Max** & **Median** & **Mean** & **CV** & \
\begin{tabular}{c} **Background Value of the** \\ **Topsoil in Guangxi, China \({}^{\text{a}}\)** \\ \end{tabular} &
\begin{tabular}{c} **Background Value of** \\ **the Topsoil in China \({}^{\text{a}}\)** \\ \end{tabular} \\ \hline As (mg/kg) & 2.36 & 162.92 & 15.60 & 23.49 & 98.32 & 8.0 & 9.1 \\ TFe\({}_{2}\)O\({}_{3}\) (\%) & 1.16 & 25.18 & 5.59 & 6.26 & 50.50 & 3.63 & 4.35 \\ Mn (mg/kg) & 29.9 & 2804.0 & 353.0 & 523.3 & 92.46 & 159 & 552 \\ Al\({}_{2}\)O\({}_{3}\) (\%) & 5.04 & 28.27 & 14.01 & 14.57 & 28.69 & 13.07 & 12.96 \\ CaO (\%) & 0.16 & 31.50 & 0.81 & 4.45 & 151.36 & 0.17 & 2.79 \\ pH & 4.97 & 8.38 & 7.18 & 7.04 & 13.83 & 5.15 & 7.15 \\ SiO\({}_{2}\) (\%) & 17.07 & 85.57 & 62.00 & 57.82 & 27.56 & 73.67 & 64.96 \\ SOC (\%) & 1.16 & 6.30 & 2.60 & 2.80 & 35.69 & 1.29 & 1.15 \\ \hline \hline \end{tabular}  
\end{table} 
Table 3: Descriptive statistic summary of the paddy soil properties (\(N=305\)). The paddy soil was primarily neutral with a median pH of 7.04, varying from 4.97 to 8.38. Notably, the median CaO content in the paddy soil was 0.81%, which was significantly higher than that in elastic and quaternary regions [38]. Research has revealed that elevated levels of Ca\({}^{2+}\) ions in the soil are a principal cause of an increased soil pH [59]. An acidic environment could increase the soluble As content in the soil; however, the desorption of As from Fe (oxyhydr)oxides in alkaline environments might result in As(III) and As(V) mobility in the soil solution, which, in turn, increases As accumulation in rice [60]. Additionally, the TF\({}_{2}\)O\({}_{3}\), Mn, and Al\({}_{2}\)O\({}_{3}\) contents in the paddy soil were 6.62%, 523.30 mg/kg, and 14.57%, respectively, which were higher than the background values of Guangxi and the rest of the country; however, the SiO\({}_{2}\) content (57.82%) exhibited the opposite trend. This indicates the desilicification-allitization of paddy soils in karst areas.