Modifying Effect of Soil Properties on Bio-Accessibility of As and Pb from Human Ingestion of Contaminated Soil

Loryssa M Lake,David J Barker,Nicholas T Basta

doi:10.3390/geosciences11030126

Abstract

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.

Highlights

Human ingestion of toxic heavy metals can have a variety of effects on health including cancer, decreased lung function, central nervous system disorders, decreased IQ, and a weakening of the skeletal system [1]
The bio-accessibility of a contaminant is dependent on its solubility, speciation, and the presence of modifying soil properties that can result in the production of insoluble solid phase compounds [7]
The objectives of this research are to (i) determine the effect of soil physicochemical properties on As and Pb bio-accessibility and (ii) identify soil properties that reduce human exposure associated with soil ingestion

Summary

Introduction

Human ingestion of toxic heavy metals can have a variety of effects on health including cancer, decreased lung function, central nervous system disorders, decreased IQ, and a weakening of the skeletal system [1]. Heavy metal contamination of soil is commonly associated with anthropogenic activities such as mining, battery production, leaded gasoline, and land application of fertilizers, coal combustion residues, and sewage sludge [2]. These contaminants include lead (Pb) and arsenic (As) [3]. Heavy metal exposure in children is often associated with ingestion of soils through hand-to-mouth activity [6].

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