The Proceedings of the Eighth International Conference on Creationism (2018)

the surrounding water. Likewise, much to all of the arsenic in the continental crust would be leached by the massive weathering of the Flood. These sources would combine to yield a significant concentration of arsenic. Under oxidizing conditions this would exist primarily as As 5+ oxides. However, these arsenic compounds would obviously not be the only compounds present in the Floodwaters. The continental crust is estimated to be 15.9% Al 2 O 3 and 6.71% iron oxides (Rudnick and Gao 2003). While there may be some variations between the modern and pre-Flood crust, these elements were still presumably a large part of the continents before the Flood. This is important because As 5+ oxoanions will readily sorb to iron oxyhydroxides. Iron oxyhydroxide is a general name for compounds of iron (mostly +3 but possible including some +2 ions) with a variable number O 2- and OH - attached. Aluminum oxide, manganese oxide, clays, and carbonates such as calcite will bind to arsenic also, but generally not as well as the iron oxyhydroxides (Henke 2009a; Meng et al. 2016; Mukherjee et al. 2014; O’Day 2006). Arsenate forms a very strong attachment to these; chemically the arsenate replaces water or hydroxide on the iron resulting in some oxygen atoms directly linking Fe and As and tightly bonding the arsenate to the iron compounds (Waychunas et al. 1996). BothAs 3+ and As 5+ oxoanions will bind, but the +5 compounds bind more strongly (Moncur et al. 2015). As +3 oxoanions bind in a way that is chemically similar to the As +5 compounds with higher pH favoring the lower oxidation state (Manning et al.1998). At a pH of less than 6, iron oxyhyroxides tend to have a net positive charge on their surface, which encourages the arsenic oxoanion to bind to them (O’Day 2006; Henke 2009a), but such binding has been computer modeled under basic conditions as well (Waychunas et al. 1996). Pure iron oxyhydroxides are not required; when the iron is released by the oxidation of pyrite, iron sulfate oxyhydroxides can result and also sorb As 5+ oxoanions (Henke 2009a). These compounds are generally insoluble and so as they precipitate they remove the sorbed arsenic from water. This principle is important for modern arsenic remediation; arsenic contaminated waters are often filtered through zero-valent iron, such as nails (which oxidizes in part as it rusts), or more successfully iron oxyhydroxides to remove the arsenic (Henke 2009b). During the Flood, massive amounts of iron would be mobilized and iron oxyhydroxides would be common in oxidizing environments. These would sorb much of the arsenic and at least some of what was not sorbed by the iron would be sorbed to carbonates or aluminum oxides (clays) greatly lowering the amount of dissolved arsenic in the water. This would be a major route for the precipitation of arsenic dissolved in the Flood waters. The sorption behavior of arsenic is effected dramatically by the presence of dissolved and suspended organic matter. On the one hand, naturally occurring organic matter can itself sorb arsenic and can dramatically increase the sorption capacity of iron; lignin is especially important in this respect (Molinari et al. 2013; Molinari et al. 2015). If the resulting arsenic-organic or arsenic-iron-organic compound is insoluble, that compound’s precipitation is a route for the removal of arsenic from water. However, organic material can also hinder the removal of arsenic from water in several ways. It often forms soluble complexes with arsenic, binding in place of the Fe and keeping the arsenic in solution. It also competes with the arsenic for binding sites on the Fe resulting in a lower sorption capacity for the iron oxyhydroxides (Redman et al. 2002). The Flood waters would, of course, contain massive amounts of organic material, essentially all the vegetation of the planet. While the chemistry involved is complex, it seems the general trend would be for this to reduce the amount of arsenic sorbed to iron oxyhydroxides by 5-10% (Redman et al. 2002). Organic material is not the only substance that competes with arsenic for sorption onto iron oxyhydroxides. Similarly, carbonate, bicarbonate, phosphate, and silica can compete with and displace arsenic from iron oxyhydroxides (Holm 2002). This effect seems especially serious due to the often high concentrations of carbonate/bicarbonate in many natural waters, and has the potential to dramatically decrease the adsorption capacity of the iron compounds and dramatically increase the concentration of arsenic in alkaline waters (Appelo et al. 2002). For example, 120 ppm inorganic carbon at pH 7 can result in an approximately 30% (or greater) decrease in the amount of arsenic sorbed (Holm. 2002). However, the sorption of arsenate over these other species is much higher at low pH; under acidic conditions this is not a significant problem (Holm 2002). This is important when we consider the Flood waters. The volcanic activity related to the Flood would presumably release a great deal of sulfur dioxide, essentially generating acid rain and lowering the pH of the Flood waters. Hydrothermal fluids were venting into the Flood waters and these fluids today are generally acidic (Ding et al. 2005; Tivey. 2007). Furthermore, the planet wide erosion of the Flood had the potential to generate something similar to acid mine drainage on a vast scale. Of course, somewhat counteracting these effects, basic salts would be dissolved by the Flood as well, but if taken as a whole it seems reasonable that the Flood waters were at least slightly acidic. If that is the case, the effect of these competing anions on arsenic sorbtion would be minimized. Redox reactions present a bigger problem. Under normal conditions there will be an equilibrium between arsenic and other competing substances for the sorption sites on iron oxyhydroxides with a great deal of the arsenic being bound at any given time. As we have seen, As 5+ sorbs more strongly than As 3+ . However, dissolved organic material can provide food for microorganisms that reduce arsenic from the +5 state to the +3 (Majumder et al. 2016). This creates a situation in which some arsenic is displaced from the iron oxyhydroxides then reduced to the +3 state. Hence it is less able to compete for its former binding site due to the decreased affinity of As 3+ oxoanions for iron compounds at low pH. This results in an overall increase in the concentration of arsenic in the water (Meng et al. 2016). Reducing water also opens the door to a process that potentially remobilizes virtually all the sorbed arsenic: the reductive dissolution of the iron oxyhydroxides. Under reducing conditions, the Fe 3+ in the iron oxyhydroxides can be reduced to Fe 2+ , resulting in the iron oxyhydroxide mineral itself dissolving and any arsenic that is bound to it being remobilized. This process is fueled by dissolved organic carbon that is relatively recently derived from surface sources (Lawson et al. 2016; Majumder et al. 2016). The carbon provides energy to bacteria and its metabolism consumes oxygen Hutchison and Bortel ◀ Fate of Arsenic in the Flood ▶ 2018 ICC 232