_Article_  
**Nano-Scale Drinking Water Treatment Residuals Affect Arsenic Fractionation and Speciation in Biosolids-Amended Agricultural Soil**  
**[PERSON] 1,*, [PERSON] 1, [PERSON] 2, [PERSON] 3 and [PERSON] 4,5**  
* 1 Department of Soil and Water, College of Agriculture, Alexandria University, Alexandria 21545, Egypt; [EMAIL_ADDRESS]
* 2 Harrow Research and Development Centre, Agriculture and Agri-Food Canada, Harrow, ON N0R IC0, Canada; [PERSON]S]
* 3 Soil Salinity & Alkalinity Laboratory, Agricultural Research Center, Alexandria 21616, Egypt; [EMAIL_ADDRESS]
* 4 Department of Environmental Sciences, Southern Illinois University, Edwardsville, IL 62026-1099, USA; [EMAIL_ADDRESS]
* 5 Department of Biological Sciences, Southern Illinois University, Edwardsville, IL 62026-1099, USA  
Arsenite presents in different valence states in the environment, including arsenide (As\({}^{3-}\)), elemental As (As\({}^{0}\)), arsenite (As\({}^{3+}\)), and arsenate (As\({}^{5+}\)). The As speciation in soil is highly depending on soil pH and redox potential (Eh). For example, arsenite becomes stable at pH 4-9 [11,12], H\({}_{2}\)AsO\({}_{4}\)\({}^{-}\) is dominant at pH 2-7, and HAsO\({}_{4}\)\({}^{2-}\) is prevailing in alkaline soils [11,13]. Arsenite and arsenate are the most dominant species in soils under aerobic conditions, and both are toxic to humans [13,14]. Therefore, As toxicity depends not only on the quantity (or the concentration) but also on its speciation. As (III) is generally more toxic to organisms than As (V). As (III) can be biologically transformed to As (V) and thus reduce As toxicity in the environment [13]. Arsenic speciation or chemical transformation influences As reactivity, mobility, and bioavailability. Therefore, it is important to determine the chemical behavior of As in agricultural soils or in other contaminated environments such as As ions, complexes, and chelates in soil solution, as well as its amorphous and crystalline forms present in soil [15]. In addition, soil microbes play important roles in As methylation, de-methylation, and oxidation/reduction, which bio-transform As into different compounds and their distribution among different environmental components [16]. For instance, As sorbs preferably to metal oxides, carbonates, and other clay minerals [13]. The As sorption capacity is also dependent on the As physical, chemical, and biological properties and adsorptive ions [17,18].  
Nanoscale particles with a diameter of \(<\) 100 nm [19, 20, 21] have a large surface area, highly porous surface, and large numbers of active adsorbing sites, compared to bulk sized adsorbent materials that made them more significant for As stabilization than micro-sized adsorbents with the same composition and/or under similar soil conditions. [PERSON] et al. [22] recently reported that mechanically-produced nanoscale drinking water treatment residuals (nWTRs) can be used as nanoparticles to sorb and reduce metal bioavailability in soils. Residues of drinking water treatment (WTRs) are a byproduct from drinking water treatment facilities and have been applied to agricultural soil in many countries because its high contents of organic matter and plant nutrients [23]. WTRs have been recently considered as green adsorbing materials for controlling phosphorus (P) and heavy metals in agricultural soils. It has been demonstrated that nWTRs greatly influence the soil active adsorbing surface area and significantly increase the soil sorption capacity [24,25].  
The objectives of this study were (1) to evaluate the ability of nWTRs for As sorption in agricultural soils, (2) to determine potential effects of nWTRs on As-fractionation and speciation in the soil amended with biosolids, and (3) to characterize treatment effects on As speciation changes using both nondestructive X-ray absorption near-edge structure spectroscopy (XANES) and a chemical equilibrium calculation Mineral-Equilibrium Model (MINEQL+ model).