## 3 Results and Discussion
### Accumulation of As in Rice Grains  
The land quality directly affects the quality and safety of crops, which, in turn, affect the health of those who rely on them. The As concentration in the rice grains ranged from 0.03 to 0.25 mg/kg, with a mean value of 0.11 mg/kg (Table 5), which was lower than that reported in many regions/countries (Table 4). [PERSON] et al. [58; 63] reported that the average As content in rice was 0.14 mg/kg in China, and 81.64% of the rice samples containing As in our study area had As contents lower than this value. The BCF\({}_{\text{As}}\) of the rice was 0.0084, which was considerably below that of other heavy metals, such as Cd, Zn, and Cu [11]. In summary, the As content in the rice grains remained low in the karst area.  
Extensive studies on As speciation have demonstrated the coexistence of inorganic and organic As in rice [65; 66]. Considering the greater levels of toxicity and carcinogenicity of inorganic As [67; 68; 69], the Ministry of Health of China states that the maximum permissible content of inorganic As is 0.2 mg/kg (GB2762-2017) [64]. Remarkably, just 0.62% of the rice  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Region/Country** & **N** & **Min** & **Max** & **Mean** & **Median** & **References** \\ \hline Rice (mg/kg) & Hunan, China & 43 & 0.05 & 0.25 & 0.13 & \(\backslash\) & [55] \\ Jiangqi, China & 30 & 0.07 & 0.25 & 0.15 & 0.15 & \\ Guangxi, China & 45 & 0.11 & 0.37 & 0.23 & \(\backslash\) & \\ Jilin, China & 4 & 0.09 & 0.16 & 0.13 & 0.13 & \\ Shanghai, China & 34 & 0.01 & 0.16 & 0.11 & 0.11 & \\ Fujian, China & 36 & 0.04 & 0.20 & 0.12 & \(\backslash\) & \\ U.S. & 163 & 0.03 & 0.66 & 0.25 & 0.25 & [56; 57; 58] \\ France & 33 & 0.09 & 0.56 & 0.28 & 0.23 & \\ Bangladesh & 144 & 0.02 & 0.33 & 0.13 & 0.13 & \\ Italy & 38 & 0.07 & 0.33 & 0.15 & 0.13 & \\ Japan & 26 & 0.07 & 0.42 & 0.19 & 0.18 & \\ Egypt & 110 & 0.01 & 0.58 & 0.05 & 0.04 & \\ \hline \hline \end{tabular}
\end{table}
Table 4: _Cont._  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Statistics** & **Total As (mg/kg)** & **BCF\({}_{\text{As}}\)** & **Inorganic As (mg/kg)** \\ \hline Min & 0.03 & 0.0004 & 0.08 \\ Max & 0.25 & 0.0530 & 0.20 \\ Median & 0.10 & 0.0058 & \(\backslash\) \\ Mean & 0.11 & 0.0084 & \(\backslash\) \\ REF a  & \\ REF (\(\%\)) means the rate of exceeding the national food safety standard (GB2762-2017) [64]. b Seven rice grain samples with a total As concentration greater than 0.2 mg/kg were selected for the determination of inorganic As concentration, and the results show that the samples of inorganic As concentrations exceeded the standard.[ENDFOOTNOTE] & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Arsenic concentration and BCF\({}_{\text{As}}\) in rice grains (\(N=305\)).  
samples had inorganic As contents above the recommended level, a far lower percentage than the 4.0% in Guangxi's non-karst region [49]; however, the proportions of soil samples that exceeded the As risk screening values and risk intervention values were 31.46% and 1.31%, respectively (GB 15618-2018) (Figure 3) [16]. The As concentrations of most of the rice grains in the paddy soil with an above-standard As content were within the safety range. A high As content but low bioavailability in rice soils in the Guangxi karst region resulted in a low As accumulation in rice. If the existing standards are strictly enforced, the use of paddy soils with an As content exceeding the standards will be restricted in agricultural production, and this is wrong and unscientific. Therefore, it is imperative to explore the causes of the low bioavailability of soil As and provide scientific support for the management of agricultural soil quality.