Tight sorption of arsenic, cadmium, mercury, and lead by edible activated carbon and acid-processed montmorillonite clay

Abstract

Heavy metal exposure in humans and animals commonly occurs through the consumption of metal-contaminated drinking water and food. Although many studies have focused on the remediation of metals by purification of water using sorbents, limited therapeutic sorbent strategies have been developed to minimize human and animal exposures to contaminated water and food. To address this need, a medical grade activated carbon (MAC) and an acid processed montmorillonite clay (APM) were characterized for their ability to bind heavy metals and mixtures. Results of screening and adsorption/desorption isotherms showed that binding plots for arsenic, cadmium, and mercury sorption on surfaces of MAC (and lead on APM) fit the Langmuir model. The highest binding percentage, capacity, and affinity were shown in a simulated stomach model, and the lowest percentage desorption (< 18%) was shown in a simulated intestine model. The safety and protective ability of MAC and APM were confirmed in a living organism (Hydra vulgaris) where 0.1% MAC significantly protected the hydra against As, Cd, Hg, and a mixture of metals by 30-70%. In other studies, APM showed significant reduction (75%) of Pd toxicity, compared with MAC and heat-collapsed APM, suggesting that the interlayer of APM was important for Pb sorption. This is the first report showing that edible sorbents can bind mixtures of heavy metals in a simulated gastrointestinal tract and prevent their toxicity in a living organism. Graphical abstract.

Keywords: Acid activation; Activated carbon; Adsorption/desorption isotherms; Heavy metals; Hydra; Montmorillonite clay.

Fig. 1

Adsorption percentage at different concentrations of As (III, V) (A), Cd (II) (B), Hg (II) (C), and Pb (II) (D) onto 1 mg/mL APM and MAC Data represent the mean percent adsorption at each concentration, run in triplicate (* p ≤ 0.05; ** p ≤ 0.01)

Fig. 2

Adsorption isotherms of As (III, V) (A), Cd (II) (B), Hg (II) (C), and Pb (II) (D) onto APM and MAC surfaces, plotted by their best fit model Data represent the mean adsorption (g/kg) at each concentration, run in triplicate

Fig. 3

Desorption isotherms of As (III, V) (A), Cd (II) (B), Hg (II) (C) onto MAC, and Pb (II) (D) onto APM surfaces, plotted by the Langmuir model Data represent the mean adsorption (g/kg) at each concentration, run in triplicate

Fig. 4

Hydra toxicity from As (III, V) (A), Cd (II) (B), Hg (C), Pb (II) (D) and a metal mixture (0.2 ppm/metal) (E)and protection by sorbents at an inclusion rate of 0.1% Hydra media and metal controls are included for comparison Data represent the mean morphological score at each time point, run in triplicate (* p ≤ 0.05, ** p ≤ 0.01)

Fig. 4

Hydra toxicity from As (III, V) (A), Cd (II) (B), Hg (C), Pb (II) (D) and a metal mixture (0.2 ppm/metal) (E)and protection by sorbents at an inclusion rate of 0.1% Hydra media and metal controls are included for comparison Data represent the mean morphological score at each time point, run in triplicate (* p ≤ 0.05, ** p ≤ 0.01)