# Usage of Si, P, Se, and Ca Decrease Arsenic Concentration/Toxicity in Rice, a Review
### Phosphorus (P) and As  
Phosphorus is a vital element required for growing plants, and plants absorb it mainly as inorganic phosphate (Pi) [49]. Phosphorus plays an essential role in the biochemistry and physiology of plants, and almost all phospholipids, nucleic acids, and ATPs contain P, which is involved in regulating significant metabolic pathways and enzymatic reactions, making phosphorus essential for the worldwide production of sustainable food [50; 51]. Agricultural products consume 90% of the extracted non-renewable phosphate reserves annually. As the population of the world increases and phosphate resources are depleted, it is necessary to improve the phosphorus use efficiency (PUE) at the plant and farm-wide scale [50; 52]. Due to the high stabilization of phosphorus in the soil and its slow release to the root surface, plants have different strategies to enable phosphorus accessibility from the ground [53]. Arsenic and phosphorus are chemical analogues. However, some of the chemical properties of P and As, including redox reactions, are distinct and cause the biochemical behaviour of the two elements to be different. As mentioned, P is an essential plant growth  
Figure 2: The effect of Adding silicon (+Si) and without silicon (\(-\)Si) treatments on arsenic concentration on different rice tissue. Nomenclature is as proposed by [PERSON], [PERSON] [46]. element, while arsenic is toxic and prevents plant growth [54,55]. In the environment, arsenic occurs as arsenate or arsenite (e.g., AsO\({}_{4}\)\({}^{-3}\) or AsO\({}_{3}\)\({}^{-3}\)); in contrast, phosphorus exists mainly as orthophosphate ions (PO\({}_{4}\)\({}^{-3}\)). Phosphates usually have many physico-chemical properties similar to arsenates, like symmetry, acid decomposition constants, and ion size, but P is more susceptible to transport sites than As (V) [55, 56, 57]. In aqueous conditions, As (V) and P (V) are present as arsenates (AsO\({}_{4}\)\({}^{-3}\)) and phosphate (PO\({}_{4}\)\({}^{-3}\)), which are surrounded by four oxygen atoms in quadrilateral coordination. Arsenate and phosphate are assumed as chemical analogues due to their being similar chemical species, which can replace each other in chemical reactions. Biogeochemical reactions often are seen as precipitation/dissolution, adsorption/excretion, and competitive/adsorption reactions in plant and microbial systems [58, 59, 60, 61]. Competitive processes of biogeochemical reaction between arsenate and phosphate control the arsenic bioavailability in the environment. However, arsenic oxidation reactions in the atmosphere produce various biogeochemical responses which do not occur for P. For instance, in anaerobic conditions like rice paddies, arsenate is transformed to arsenite because it is not absorbed as much as arsenate on soil particles (especially at low or neutral pH), so, it is more mobile and soluble. Redox mobility creates arsenic distribution in sediments and soils that decreases under fluctuations of oxidation, but P is not changed by redox variation [62]. An experiment on disposal of arsenate showed after using phosphate solutions, only 35% of the adsorbed arsenate was absorbed from goethite, which indicates that the arsenate bonds were more substantial than the phosphate bonds on iron oxide. The toxicity mechanism in organisms is maybe metabolic substitution of arsenate for phosphate [63]. Under aerobic conditions, As (V) and phosphorus (Pi) due to similar chemical properties, stable quadrilateral oxidants form the oxidation state p5. However, there is less correlation between the behaviour of phosphate and arsenite under aqueous conditions because phosphate is not an analogue of As (III), and arsenite transport is not affected by phosphate [64,65]. However, arsenite oxidation to arsenate is distinct in the rice root region [66]. Thus, the effect of phosphate on the behaviour of arsenite in the rhizosphere cannot be completely ignored, and actual cognition of this feature is needed.