Exposure to soils contaminated with heavy metals can pose human health risk to children through ingestion of contaminated soil. Soil properties such as soil pH, reactive Fe and Al oxide content, clay content, soil organic matter (SOM), and cation exchange capacity (CEC) can reduce contaminant bio-accessibility and exposure. In vitro bio-accessibility (%IVBA) of As and Pb in 19 soils was determined using U.S. EPA Method 1340. Soil properties reduced the bio-accessibility of As by 17–96.5% and 1.3–38.9% for Pb. For both As and Pb, bio-accessibility decreased with increasing Al and Fe oxide content. Al oxides were found to be the primary driver of As and Pb bio-accessibility. Multiple regressions with AlOx, soil pH, %clay and/or FeOx predicted %IVBA As (p < 0.001). The multiple regression including log (FeOx + AlOx) and %clay explained 63% of the variability in %IVBA Pb (p < 0.01). Fe and Al oxides were found to be important drivers of As and Pb bio-accessibility, regardless of in vitro method. These findings suggested soil pH should be used in addition to reactive oxides to predict bio-accessible As. Risk-based adjustments using soil properties for exposure via incidental ingestion should be considered for soils contaminated with As and/or Pb.

Urban soils contaminated by historical and current anthropogenic activities present an alarming human health risk requiring redress. Federal and state governments continue to lower residential soil lead (Pb) screening standards, which will likely require new risk‐based approaches to address urban soil Pb contamination. Phosphorus (P) soil amendments have long been presented as a solution to sequester Pb, thereby reducing exposure risk. In this study, P‐containing sources (biosolids incinerator ash, poultry litter, biosolids compost, and triple superphosphate) of varying solubilities were assessed as soil amendments to reduce Pb bioaccessibility and serve as an inexpensive remediation strategy for urban soil. Contaminated soil (1624 mg kg⁻¹ Pb, pH 7.43) from Cleveland, OH, was treated with the four P‐containing soil amendments at a 1:5 Pb:P molar ratio and two combination treatments at 1:10 Pb:P molar ratio and incubated for 3 months. A batch equilibration analysis was also conducted to assess reduction in in vitro bioaccessible Pb (IVBA Pb). Pb bioaccessibility was evaluated using US EPA Method 1340 at pH 1.5 and the Physiologically Based Extraction Test pH 2.5 at 1 and 3 months. In general, treatments were ineffective in reducing IVBA Pb regardless of IVBA extraction method, incubation duration, batch equilibration analyses, or P source. The results of this study suggest P‐containing amendments are not suitable to address Pb exposure in the study soil. Site‐specific efficacy testing to determine reductions in IVBA Pb from P‐containing amendments should be performed before making recommendations for remediation of Pb‐contaminated urban soil.

Solutions are needed to address increasing concerns over degraded land and global food insecurity. One solution is to design soil blends that can restore soil quality and fertility. Dredge material has many soil‐like properties, which makes it a good candidate for the main component of manufactured soil blends. Questions have arisen over contaminants of concern (heavy metals and polyaromatic hydrocarbons [PAH]) in dredge fines precluding them from reuse. One approach is to remove the fine fraction of dredge to lower the contaminant concentration; however, it may result in a lower quality soil substitute for land reclamation. In this study, soil blends were designed to compare the use of whole dredge to dredge fines (e.g., dredge with silt and clay fraction) and to assess the benefits of compost material, clay, and fertilizer additions. Dredge fines blends led to increases in soil quality, dry matter growth, plant available water, total and active C, potentially mineralizable N, and micronutrients. The addition of compost material led to better soil quality for a vast majority of the tested parameters. Dredge fines were below regulatory standards for contaminants of concern (e.g., carinogenic polyaromatic hydrocarbon and heavy metals), allowing their reuse in soil blends. Removal of fines from dredge decreases the quality of soil blends and should not be removed from dredge material for use as topsoil or in topsoil blends. The 80% (v/v) dredge fines blend with 20% (v/v) additions of compost material resulted in the greatest improvements in the assessed soil health parameters.