Use of the Physiologically Based Extraction Test for the Assessment of Bioaccessibility of Toxic Metals in Vegetables Grown on Contaminated Soils

Abstract

BACKGROUND: An important concern for human health is the uptake of toxic metals by vegetables from soils and their consumption by humans. OBJECTIVES: To assess the oral bioaccessibility of metals in vegetables (spinach, pumpkin, celosia, okro leaves and waterleaf) grown on contaminated soils collected from five different sites in Lagos, Nigeria. METHODS: The soil and vegetables were acid digested and the total metal concentrations (copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb) and zinc (Zn)) were determined using a flame atomic absorption spectrophotometer. A bioaccessibility study of the edible parts of the vegetables was estimated using the modified in vitro physiologically based extraction test (PBET). RESULTS: The results for total concentration showed that individual vegetable types differed in their levels of metal uptake. The values were in the range of 0.5-13.5 mg/kg for Cd, 2.0-221 mg/kg for Cu, 2.5-37.7 mg/kg for Cr, 10-250 mg/kg for Zn. Pb was below the detection limit. The transfer factor from soil to vegetable followed the order of Cd >Zn > Cu > Cr >Pb. DISCUSSION: For the PBET study, metals were solubilized mostly in the gastric phase, and the results varied in the range of 0.4-114.4 mg/kg for Cu, 0.1-2.4 mg/kg for Cd, and 0.8-137 mg/kg for Zn, but there was little or no bioaccessibility in the intestinal phase. Cr and Pb were non-detectable in either the gastric or intestinal phase. CONCLUSIONS: Although the level of metals (Cd, Cu and Zn) available for absorption in the gastric phase were found to be low in most of the vegetables studied, the experiment revealed that metals are likely released in the human gut after intake of vegetables grown on contaminated soil.