Bioaccessibility of Metals in Soils for Different Liquid to Solid Ratios in Synthetic Gastric Fluid

Abstract

The bioaccessible fraction of metals in the stomach has been estimated for two soil materials using laboratory synthesized gastric juice. Heavy metals present in each soil matrix were extracted and measured, as a technique to simulate metal solubilization processes that occur in the human stomach. The results from the synthetic gastric juice extraction were compared to values obtained using a modified EPA concentrated acid extraction procedure, method 3051, on the same soils. The experiments evaluated the effect of varying the liquid to solid ratio on gastric juice extraction efficiency for arsenic (As), chromium (Cr), nickel (Ni), cadmium (Cd), and lead (Pb). Soil samples employed were a National Institute of Standards and Technology (NIST) standard soil (Montana SRM 2710) and a composite hazardous waste contaminated soil from Jersey City, NJ. The current work demonstrates that bioaccessibility is not the same for each metal within a given soil, nor between the soils. Estimates of the bioaccessible fraction of the metals studied ranged from 2 to 61% of the NIST certified values for Montana soil, and from 3% to 58% of EPA method 3051 values in contaminated Jersey City soil. The experiments indicated that the bioaccessibility of metals in the soils extracted by the in vitro synthetic gastric juice will only be affected slightly by changes in gastric fluid liquid to solid ratios for the range 100:1 to 5000:1 (mL/g). Further, the masses of each soil (0.05 or 0.5 g) used did not affect the bioaccessibility at the 1000:1 ratio.