bioavailability of heavy metals

Overview

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Key numbers

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, Anika Singh1 & David D. Kitts1 ✉
the Unified Bioaccessibility Research Group of Europe (UBM) method and the Caco-2 permeability
estimates using the Caco-2 cell showed very low to non-detectable permeability for all 3 heavy metals.
Thus, while initial heavy metal ranged from 3.8–17 ppm, 0.024–0.061ppm, and 5.8–20 ppm for As, Cd,
non-detectable values of As, <0.007ppm of Cd, and <0.1ppm of Pb. Using UBM-digestion to mimic
bioaccessibility, followed by Caco-2 cell bioavailability enabled us to conclude that in vitro assessment
soreness, as well as a treatment for other chronic disease1,2. Mineral clay acidic extracts, in particular, are known
the thinning of cartilage tissue3. Several clinical studies also report that naturally found mineral clays have the
which translates to a substantial cumulative economic burden that has an estimated cost of $195.2 billion8. The
exceed current Health Canada’s tolerance limits, established for heavy metals present in natural health products9.
thus available to induce a potentially toxic effect10,11. For our purposes, bioaccessibility was determined by the
Food, Nutrition, and Health, Faculty of Land & Food Systems. 2205 East Mall, University of British Columbia,
Vancouver, BC, V6T 1Z4, Canada. 2School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu,
Table 1. Total As, Cd, and Pb content in mineral clay (ppm; mean ± SD).
which may act to sequester metals are known factors that will influence the extent of metal bioaccessibility12,13.
using cultured Caco-2 cells, which assesses transfer behaviour and uptake of heavy metals14,15. Bioaccessibility
water samples; agricultural crops and commodities such as, vegetables, seafood and natural health products14–19.
data, reinforces its practical use to predict the exposure of heavy metals to humans16,20–22. The procedure also
logically based extraction test (PBET)23 and the in vitro gastrointestinal method (IVG)22; and a three-step, Unified
metal toxicity in the soil matrix24. The BARGE method has also been used to determine metals availability in fish
and crab food sources25. The simulation consists of two phases; the gastric and gastrointestinal phase, where the
samples are digested with enzymes that simulate gastric and small intestine combined19,24. The USEPA method
metabolism and the interaction with the gut microbiota, all can potentially influence the level of bioavailability26.
present in natural health products. The Caco-2 cell, a human colon adenocarcinoma cell line, has numerous
fully differentiated27–33. For these reasons, the Caco-2 cell has been shown to have usefulness to assess the in vitro
bioavailability of heavy metal components in food products following gastric or gastrointestinal digestion15.
Caco-2 monolayer permeability assay. This combination of bioaccessibility followed by bioavailability assessment
Total As, Cd, and Pb in clay samples. The total As, Cd, and Pb concentrations in 10 batches of mineral
clay samples are presented in Table 1. A wide range of heavy metal concentrations that included As (4–17 ppm);
Cd (24–61 ppb) and Pb (6–20 ppm) were found. Results showed that As and Pb contents in clays collected from
contents in soil and clay samples34,35. Moreover, variation in total heavy metal content, specifically for Pb, was also
observed from different collecting times made at the same site (Sample 1–2 and Sample 3–5); an observation that
pH of individual clay aggregates sampled herein could have been a factor since low pH (e.g. pH < 5) characteris-
tics are known to correspond to greater solubility of lead salts12.
Table 2. Bioaccessibility (%) of As, Cd, and Pb measured by UBM and USEPA methods. Data are expressed
significantly (P < 0.05) greater than that of UBM-GI methods. a,bBioaccessibility of As extracted with UBM-G
and UBM-GI methods is significantly different (P < 0.05) between samples obtained from site 1 and site 2.
Bioaccessibility of Cd extracted with UBM-GI methods is significantly different between (P < 0.05) samples
obtained from site 1 and site 2. d–fBioaccessibility of Pb extracted with different methods is significantly different
(P < 0.05) between site 1 samples obtained from different time periods. gBioaccessibility of Cd extracted with
UBM-GI methods is significantly different (P < 0.05) between site 1 samples obtained from different time
From the results presented in Table 1 and the recommended dosage of most commercially available mineral

Methods (brief)

Cadmium (Cd) and Lead (Pb) in mineral clay samples collected from the Sierra Mountains (USA) using
assay, respectively. After UMB-gastric (UBM-G) digestion, As and Pb bioaccessibility were lower
non-detectable values of As, <0.007ppm of Cd, and <0.1ppm of Pb. Using UBM-digestion to mimic
released from a mineral matrix into the gastrointestinal tract upon digestion; while the term “bioavailability”
maximum soluble concentration of metals that were released from the sample clay mineral matrix using a syn-
thetic oral, gastric and intestinal medium, equipped with enzymes to simulate gastrointestinal digestion. Factors
Further risk assessment can be made by conducting in vitro bioavailability of the heavy metals following digestion
water samples; agricultural crops and commodities such as, vegetables, seafood and natural health products14–19.
Several standard methods are available to measure heavy metal bioaccessibility in mineral clay samples. Most
gastric phase has samples treated with fluids that mimic the stomach fluid and the gastrointestinal phase where
samples are digested with enzymes that simulate gastric and small intestine combined19,24. The USEPA method
was initially established to measure Pb in soil samples and the same has never been tested on other matrices,
the composition of digestion solution, the sample to solution ratio, and digestion time16,17.
bioavailability of heavy metal components in food products following gastric or gastrointestinal digestion15.
Total As, Cd, and Pb in clay samples. The total As, Cd, and Pb concentrations in 10 batches of mineral
clay samples are presented in Table 1. A wide range of heavy metal concentrations that included As (4–17 ppm);
Cd (24–61 ppb) and Pb (6–20 ppm) were found. Results showed that As and Pb contents in clays collected from
different sites (Sample 1–5 versus Sample 6–10) were quite variable. Indeed, factors specific to the sampling sites,

Implications

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
3171d06	2026-08-02	major	1 section added
bc84bfc	2026-08-02	major	6 sections added; narrative text revised