Continuous On-Line Leaching for Bioaccessibility Analysis in Human Health Risk Assessments with Inductively Coupled Plasma Mass Spectrometry
bioaccessibility , human health risk assessment , soil bioaccessibility , inductively coupled plasma mass spectrometry , ICPMS , HHRA , risk assessment , on-line leaching , toxic elements , inorganic contaminants , lead , arsenic
Soil is a natural resource that is vital for local ecosystems, agriculture, and sustainable development. The contamination of soils can have disastrous effects on human health, but a human health risk assessment (HHRA) can indicate these effects, associated risks, and potential remediation strategies. Since incidental soil ingestion is a major pathway for exposure, bioaccessibility is often employed in an HHRA. Bioaccessibility is the proportion of a contaminant that is dissolved in gastrointestinal fluids, which can be measured using in vitro methods. It differs from bioavailability, which is the actual amount absorbed into the circulatory system. Bioaccessibility methods can be validated through a direct comparison with time consuming animal bioavailability studies, as was done for a method used by United States Environmental Protection Agency (US EPA) and the Unified Bioaccessibility Method (UBM). This thesis first gathered gastric and intestinal bioaccessibility data from the last 28 years to look at the influence of key parameters. It indicated significant Spearman correlations between elements, including Pb and As, which could aid risk assessors. An additional lack of Al, Sb, Fe, Mn, and Hg data was observed and these elements should be included in future risk assessments. Next, these bioaccessibility data were used to compute risk based soil concentrations incorporating bioaccessibility, which indicated that bioaccessibility would be useful in an HHRA only at sites with low concentrations of As, Sb, and Cd, but could refine the risk estimates for Al, Fe, and Cr in all scenarios. Then, a continuous on-line leaching method (COLM) using a high-pressure extraction setup was demonstrated to provide similar results as the validated US EPA and UBM bioaccessibility methods but in a fraction of the time. For the first time, the COLM was also used to assess the effect of toasting on the bioaccessibility of As, Cd, and Pb in gluten free and rye bread. Although As, Cd, and Pb were mostly bioaccessible, whether the bread was toasted or not, toasting lowered their concentrations by 1.5-2.5 fold. Finally, the unique dynamic kinetic extraction information afforded by the COLM allowed for the identification of Pb isotope ratios that matched tetraethyl lead in both the reference soil BGS 102 and rye bread samples.