Assessment of bio-accessibility of heavy metals (Cd, Pb, and As) through consumption of medicinal plants collected from different regions in Nyamira- Kenya

Background: In this study, the total and bio-accessible levels of cadmium (Cd), lead (Pb), and arsenic (As) in 19 Kenyan medicinal plants from two regions (Manga and Borabu) are presented. Methods: Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total and bio-accessed heavy metals in plants. The NIST 1647 plant reference material was used to study the performance of the method. The method offered excellent quality parameters in terms of detection and quantification limits of 0.08 and 0.24 µg/kg, 0.5 and 1.5 µg/kg, and 3.1 and 9.5 µg /kg, linearity (r2 > 0.997) and recoveries of 95%, 99% and 93% for Cd, Pb, and As, respectively. Results: The dry weights of the plants from Manga and Borabu showed low concentrations of Cd (270 ± 20 and 260 ± 20), As (320 ± 20 and 480 ± 40), and Pb (1230 ± 110 and 1160 ± 100) µg/kg. Significantly higher mean concentrations of Cd, Pb, and As (0.45 ± 0.11, 0.46 ± 0.12 and 0.37 ± 0.10 µg/kg) than (0.32 ± 0.07, 0.34 ± 0.11 and 0.26 ± 0.08 µg/kg) were bioaccessible enzymatically than aquatically from dry weight (p<0.05). The percentage bioaccessibility of the elements from the plants ranged from 0.08 to 10.66% and 0.02 to 2.56% for the enzymatic and aquatic procedures, respectively.  Conclusion: The low bioaccessible concentrations of heavy (toxic) elements in plants justify their therapeutic use.