# Usage of Si, P, Se, and Ca Decrease Arsenic Concentration/Toxicity in Rice, a Review
### Arsenic (As) and Rice  
Arsenic is a carcinogenic metalloid, and humans are contaminated mainly through diet and drinking water., increasing health problems [14]. The National Toxicology Program and International Agency for Research on Cancer categorized arsenic as the first carcinogenic agent [15; 16]. There are various species of As in nature, and they are listed in Table 1. More than other grains, rice accumulates arsenic in its tissues [17]. The kinds of As in rice are mainly inorganic (iAs, including arsenate and arsenite), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) [18]. According to research, inorganic kinds of As are more toxic than DMA and MMA [19], and under anaerobic situations, As (III) is the prevailing type in soil solutions [20]. Increased arsenic release from soil particles by rice occurs through competition with soil mineral adsorption sites [22]. In anaerobic environments, arsenic motility and viability are significantly increased [20]. Paddy fields are an excellent environment for increasing arsenic bioavailability--the amount of arsenic absorption is such that it can enter the rice and affect rice growth--because the rice plants are grown in flooded conditions [23]. Therefore, since arsenic has a high solubility in water, this element is the most critical pollutant [24]. Arsenic contamination has become the reason for significant health difficulties in humans and animals [25], and in India, China, Sri Lanka, Pakistan, Nepal, Bangladesh, Chile, Mexico, and Argentina, pollution of drinking water sources with arsenic is now a public health emergency [26]. In some mines in southern China's Guangdong, the soil is heavily polluted with arsenic and some other heavy metals, and according to some studies, pollution in agricultural lands around these mines has reached 344.11 mg/kg, which indicates an excessive concentration of arsenic (1 to 40 mg/kg) in the soil [27]. There are two main ways to absorb arsenic in rice: (1) As (V) as a chemical analogue of phosphate is absorbed in rice roots by the phosphate transport protein system. (2) As (III) is an analogue of silicic acid and can be absorbed via the roots of rice with the delivery systems of silicic acid (_Lsi1_ and _Lsi2_) (Figure 1) [28; 29]. As mentioned, there are two main pathways for arsenic uptake by rice, so because we wanted to investigate the role of microelements and macroelements in reducing toxicity and uptake of arsenic, we looked at elements that have a common uptake pathway with arsenic. Among them, we examined two macroelements (P, Ca) and two microelements (Si, Se) that effectively reduce the toxicity and absorption of arsenic in rice. Several methods are used to determine the bioavailability and concentration of arsenic in rice, including the in vitro digestion process to determine the bioavailability of arsenic [31] and the Meharg and Jardine [32] method to determine the concentration of arsenic in rice. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Arsenic Compounds** & **Acronyms** & **Chemical Formula** \\ \hline Arsenate & As (V) & As(O\({}^{-}\))\({}_{3}\) \\ Arsenite & As (III) & O=As(O\({}^{-}\))\({}_{3}\) \\ Methylarsonate & MMA & CH\({}_{3}\)AsO(O\({}^{-}\))\({}_{2}\) \\ Dimethylarsinate & DMA & (CH\({}_{3}\))\({}_{2}\)AsO(O\({}^{-}\)) \\ Trimethylarsin oxide & TMAO & (CH\({}_{3}\))\({}_{3}\)AsO \\ Tetramethylarsonium ion & TETRA & (CH\({}_{3}\))\({}_{3}\)As\({}^{+}\) \\ Arsenobetain & AB & (CH\({}_{3}\))\({}_{3}\)As\({}^{+}\)CH\({}_{2}\)COO\({}^{-}\) \\ Trimethylarsoniopropionate & TMAP & (CH\({}_{3}\))\({}_{3}\)As\({}^{+}\)CH\({}_{2}\)CH\({}_{2}\)COO\({}^{-}\) \\ Arsenocholine & AC & (CH\({}_{3}\))\({}_{3}\)As\({}^{+}\)CH\({}_{2}\)CH\({}_{2}\)O\({}^{-}\) \\ Dimethylarsinoylacetate & DMAA & (CH\({}_{3}\))\({}_{2}\)(O)As\({}^{+}\)CH\({}_{2}\)COO\({}^{-}\) \\ Dimethylarsinoylpropionate & DMAP & (CH\({}_{3}\))\({}_{2}\)(O)As\({}^{+}\)CH\({}_{2}\)CH\({}_{2}\)COO\({}^{-}\) \\ \hline \hline \end{tabular} Nomenclature is as proposed by [PERSON] and [PERSON] [21].  
\end{table}