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Degree

Master of Science, Ohio State University, Soil Science, 2009.

Abstract

In vitro gastrointestinal methods can potentially provide a rapid and inexpensive measure of bioaccessible arsenic which in turn can be used to conduct more accurate and site-specific human health risk assessments of contaminated soils. However, in order for in vitro methods to become widely accepted as tools that accurately assess soil As exposure through the oral ingestion pathway, a better understanding of the fractions of soil arsenic that are measured by the in vitro extraction and the underlying soil properties associated with As bioaccessibility (BA) are needed. In this study, nineteen soils with a wide range of soil properties were spiked with 250 mg/kg As. Bioaccessible As was then determined using The Ohio State University in vitro gastrointestinal method (OSU-IVG) and soil As was fractionated using a four-step sequential extraction. There was a wide range in As BA; from 27.3 to 206 mg/kg with a mean of 94.7 mg/kg in the gastric phase, and from 29.0 to 210 mg/kg in the intestinal phase with a mean of 98.6 mg/kg. Highly significant (P < 0.0001) relationships existed between bioaccessible As and the combination of soil pH and Fe extracted by citrate bicarbonate dithionite (Fecbd) or soil pH and Fe extracted by acid ammonium oxalate (Feox). Soil pH explains more of the variation in bioaccessible As (r² = 0.67) than Fecbd (r² = 0.45) or Feox (r² = 0.38). The sequential extraction results indicate that As extracted from non-specifically sorbed (F1) and specifically sorbed (F2) fractions provide a good measure of pH and iron oxide (Fecbd and Feox) controlled As BA (GE, r² = m = 1.06; IE, r² = 0.94, m = 1.07). However, the addition of amorphous or poorly-crystalline oxides of Fe (F3) and well-crystallized oxides of Fe (F4) as extractable As fractions to F1 and F2 dies not improve the correlation with bioaccessible As. Therefore, the total As content of soil overestimates and is a poor indication of bioaccessible As. The largest contribution to bioaccessible As is the specifically sorbed (F2) fraction of soil As. Because F2 As is the largest contribution to bioaccessible As, it is the strong linear relationship between F2 and soil pH that controls the relationship between bioaccessible As and soil pH. Accurate and site specific HHRAs are necessary in order to prevent the use of overly conservative assumptions that would result in unnecessary site remediation. The use of As BA in HHRA as determined by valid in vitro methods supported by soil property and As fractionation results could potentially provide enormous cost and time savings for superfund site managers while assuring protection to public health.

Subject Headings

Environmental science

Keywords

Arsenic; Arsenate; soil properties; fractionation

Committee / Advisors

Nicholas Basta (Advisor)
Jerry Bigham (Committee Member)
Linda Weavers (Committee Member)
Elizabeth Dayton (Committee Member)

Pages

43p.

Document number: osu1244036619
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1244036619

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