33As is abundant and variable in soils. Using USGS data on As and geostatistical methods a map for USA shows that As exceeds guidelines for many areas of the USA. As geochemistry requires study to elucidate potential human health risks. The forms are arsenite (ANI) and arsenate (ANA) that are carried in solution. ANI is stable in reducing conditions and ANA in oxidizing. Eh and pH can change forms from ANI and ANA in soils. ANA acts similar to P in soils and methods to reduce mobility are similar. These are: 1) precipitation or 2) absorption onto mineral surfaces. Using soluble P as a surrogate for As we conducted field studies over 4 yr to collect runoff from soil amended with gypsum. Applications of gypsum reduced soluble P in runoff 75% over a control (P>0.01). As would be further reduced because published values for Ksp for various Ca-ANA range from 10-21 to 10-40 when Ca/As was >1.5. Since gypsum produces much soluble Ca then As would be precipitated.  Studies were conducted directly on As in soils. Four iron-containing materials: Fe2(SO4)3, FeCl3, zero-valence Fe, and Fe-water treatment residual (WTR) were evaluated for remediation of three As-contaminated soils and one slag waste. Risk from multiple human exposure pathways were evaluated by the following soil chemical methods. The Bray soil test method and pore water was used to evaluate phytoavailable As. Potential exposure via the soil ingestion pathway was determined by measuring bioaccessible As using the OSU IVG method. All amendments were effective in reducing pore water, plant available and bioaccessible As. Reductions were 50 to >90%. Our results show that the Fe-containing amendments may be used as amendments to reduce risks to human health and to the environment of As in As-contaminated soils.

Potential for soil amendments to reduce concentrations of As in soils and waters

245th National Meeting (2013)

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