Fu and Xi 2019 — Heavy metals and human metabolism

Fu and Xi review the metabolic mechanisms by which five heavy metals — lead, arsenic, cadmium, nickel, and mercury — disrupt human physiology. The paper is mechanism-oriented, anchored in oxidative stress and reactive oxygen species generation as the common toxicity pathway, and draws on occupational exposure literature, drinking-water contamination studies, and experimental cell and animal work. The authors frame contaminated drinking water as the primary human exposure route and explicitly limit the scope to mechanisms and metabolic effects rather than food-occurrence quantification.

Key numbers

The review reports very few primary quantitative claims; what it cites is drawn from other sources and used as exposure context.

• Drinking water exposure context (arsenic, attributed to Lenczewski 2009 and Rahman 2002): more than 140 million people worldwide consume drinking water that exceeds the WHO 10 ppb (µg/L) guideline for arsenic; 35 to 77 million people in Bangladesh and West Bengal are exposed to arsenic concentrations ranging from less than 10 ppb to more than 4 ppm (4 mg/L), with the cited authors attributing the death of roughly 1 in 5 of the exposed population to arsenic exposure (the source phrasing — “the death of about 1/5 people due to exposure to arsenic” — is ambiguous between this and a “1 in 5 of all deaths” reading; the population-mortality reading is the more natural parse).
• Arsenic-induced Warburg effect (Zhao et al. 2013, cited): chronic exposure of cultured human cells to 75 ppb arsenite produces a shift from mitochondrial oxidative phosphorylation to aerobic glycolysis, dependent on HIF-1α stability (Zhao et al. 2014, cited).
• Lead occupational exposure context (Patocka and Cerny 2003, cited): more than 900 occupations involve lead exposure, including refining, mining, smelting, welding, and pigment and glass manufacture.
• Glutathione baseline in normal cells (Samadi et al. 2001, cited): reduced GSH accounts for roughly 90% of total cellular glutathione and oxidized GSSG for roughly 10% under normal conditions; the ratio inverts under oxidative stress.

No new occurrence data, primary measurements, dose-response curves, or food-matrix concentration values are reported in this paper; it does not contribute to ingredient or product contamination_profile cells.

Key mechanisms covered

Lead. The review describes two mechanism families: direct production of reactive oxygen species (O₂⁺, H₂O₂, hydroperoxides) by lead in cells (citing Ercal, Aykin-Burns, and Gurer-Orhan 2001), and consumption of antioxidant defenses, principally glutathione. Lead inhibits mitochondrial oxidative phosphorylation, alters δ-aminolevulinic acid dehydratase (ALAD), and elevates malondialdehyde (MDA) in occupationally exposed workers (Kasperczyk 2005; Permpongpaiboon 2011, cited). Lead can substitute for calcium and other divalent cations (Ca²⁺, Mg²⁺, Fe²⁺) and even monovalent Na⁺, disrupting protein kinase C at picomolar concentrations (Flora, Mittal, and Mehta 2008, cited). The paper reports conflicting findings on lead’s effect on G6PD activity in red blood cells (Kasperczyk 2005 reported decreased activity; WHO 2004 reported increased activity in lead-exposed workers).

Arsenic. The review summarizes arsenic metabolism in the figure-3 pathway: arsenate (As(V)) is reduced to arsenite (As(III)) by glutathione, then methylated (with S-adenosyl methionine as methyl donor and glutathione as cofactor) to monomethylarsonic acid (MMA, in both V and III oxidation states) and dimethylarsinic acid (DMA, in both V and III oxidation states). Most ingested inorganic arsenic is excreted in urine. The paper cites arsenic effects on skin (Yu, Liao, and Chai 2006), bladder (Marshall et al. 2007), liver (Liaw et al. 2008), kidney (Yuan et al. 2010), and lung (Smith et al. 2006) cancers. Mechanism candidates discussed include reactive oxygen species production (Shi, Shi, and Liu 2004), altered DNA methylation (Zhao et al. 1997), DNA damage (Wang et al. 2001), enzyme inhibition (Kitchin and Wallace 2008), mitochondrial enzyme suppression (pyruvate, succinate, isocitrate, α-ketoglutarate dehydrogenases), electron-transport-chain dysfunction at complexes II and IV (Naranmandura et al. 2011), and inhibition of hexokinase-2 (Zhang et al. 2015).

Cadmium. The review describes cadmium binding to metallothionein (MT) in the body to form Cd-MT, which is reabsorbed in the proximal kidney tubule and degraded in lysosomes, releasing free cadmium that interferes with mitochondrial energy metabolism and oxidative phosphorylation in proximal-tubule epithelial cells (Jomova and Valko 2011; Ohta and Cherian 1991, cited). Cadmium produces ROS by displacing copper and iron from binding sites, triggering Fenton reactions. The paper identifies the mTOR pathway and mitogen-activated protein kinases (MAPK) as the two ROS-driven signaling pathways implicated in cadmium-induced neuronal apoptosis (Chen et al. 2008; Chen et al. 2011, cited). Cadmium inhibits fructokinase phosphate in liver and muscle (Almeida et al. 2001, cited), inhibits hexokinase (Ramirez-Bajo et al. 2014, cited), and shows biphasic effects on glycolysis (initial promotion, later inhibition; Zhou, Lei, and Wang 2012, cited). The paper identifies oral intake of contaminated food and water as the dominant exposure route for non-smokers without occupational exposure (Pang et al. 2016, cited), but does not quantify dietary cadmium intake or distinguish food sources.

Nickel. The review describes nickel binding to mercaptan (thiol-containing proteins) to form a nickel-mercaptan complex that reacts with molecular oxygen to produce free radicals (Das et al. 2006, cited). Nickel binding to thiol proteins depletes glutathione (Valko, Morris, and Cronin 2005, cited) and reduces calcium excretion and nitrogen retention (Kumar et al. 2019, cited). The paper cites induction of oxidative stress in cultured human red blood cells (M’Bemba-Meka, Lemieux, and Chakrabarti 2006) and oxidative-stress-driven cell death via Redox-homeostasis disruption (Oukarroum et al. 2017). Cited oral nickel exposure pathways are water and food contaminated with nickel-containing compounds (Haber et al. 2000); the paper does not quantify food-source nickel or enumerate specific commodities.

Mercury. The review distinguishes three forms — elemental mercury, inorganic mercury, and organic mercury — with different toxicity profiles (Clarkson 1997, cited). Elemental mercury vapor is absorbed through the respiratory tract, distributes across the cell membrane and blood-brain barrier, and is oxidized to Hg²⁺ in red blood cells and tissues. Inorganic mercury accumulates in kidneys and can cause acute renal failure (Al-Saleh, Al-Sedairi, and Elkhatib 2012, cited). Methylmercury is described as a neurotoxic compound causing lipid peroxidation, mitochondrial damage, microtubule damage, accumulation of neurotoxic molecules (Patrick 2002, cited), elevation of free Ca²⁺ in cerebral-cortex nerve cells, and oxidative stress via interference with mitochondrial respiratory chains (Ho et al. 2013, cited). Mercuric chloride (HgCl₂) is identified as carcinogenic (Risher et al. 1999, cited) and shown to damage mitochondrial intima (Nava et al. 2000, cited) and alter membrane permeability (Mahboob et al. 2001, cited). In red blood cells, HgCl₂ inhibits both hexokinase (first glycolytic enzyme) and pyruvate kinase (last glycolytic enzyme) (Anastasiou et al. 2011; Schutt et al. 2012, cited). The paper cites mercury as a causative agent of autoimmunity (Crowe et al. 2017), Alzheimer’s disease, and Parkinson’s disease (Chin-Chan, Navarro-Yepes, and Quintanilla-Vega 2015).

Methods

This is a narrative review, not a systematic review or meta-analysis. The authors describe their scope as an overview of heavy-metal pollution status, metabolic-enzyme effects, and possible mechanisms of action. No PRISMA protocol, search strategy, inclusion criteria, or quality-weighting of cited studies is described. The reference list draws on roughly 90 sources spanning 1965 to 2019, with most heavily cited primary literature from 2000-2018.

Limitations

• The abstract and opening framing emphasize contaminated drinking water as “the main source of human exposure to heavy metals,” a claim repeated throughout. For dietary-exposure questions, this paper is not the right secondary source.
• The paper presents no occurrence data, no dose-response curves, no LODs or LOQs, and no measurements. Every quantitative claim is attributed to a cited source.
• Several mechanism statements rest on single cited studies (often from in vitro or animal work) without weighing contradictory evidence.
• A handful of in-text phrases appear to be typos or translation artifacts (e.g., “pentapriced” for “pentavalent”, “triaval” for “trivalent”, “dimethylric acid” for “dimethylarsinic acid”, “Hg in red blood cells” passages), reflecting the accepted-manuscript stage. This does not affect mechanism interpretation but is worth flagging.

Implications

Certification: not applicable. The paper sets no occurrence values, no dose-response floors at food-relevant concentrations, and no thresholds.

Health and toxicology: useful as a peer-reviewed mechanism overview for the per-metal toxicology sections of lead, cadmium, arsenic-total, arsenic-inorganic, mercury-total, mercury-methyl, and nickel. Treat as a secondary entry point; for dose-response and population-level synthesis use EFSA scientific opinions and JECFA monographs (A-tier) instead.

Courses: usable for mechanism-of-action teaching content, with the caveat that the drinking-water and occupational framing should be made explicit to learners and that primary toxicology references are preferable for advanced material.

App: not applicable. No food-form or contamination-likelihood data.

Wiki pages this source may touch

• lead
• cadmium
• arsenic-total
• arsenic-inorganic
• mercury-total
• mercury-methyl
• nickel

Verification notes

• 2026-05-18 (audit subagent finding, applied): Audit subagent flagged the Bangladesh/West Bengal “1 in 5 deaths” phrasing as a slight tightening of the source’s ambiguous “death of about 1/5 people due to exposure to arsenic” claim. Verified against PDF p. 12; the more natural reading is “1/5 of the exposed population dies from arsenic exposure,” not “1/5 of all deaths in the population are arsenic-attributable.” Rephrased to track the source phrasing and flag the ambiguity inline.
• 2026-05-18 (Claude session, merge-enhance): Full 34-page PDF re-read. Prior page (updated 2026-05-15, raw_handle: papers-cube) was correct in outline but contained substantive synthesis claims that did not trace to fu2019. Removed: CDC blood-lead-no-threshold position (paper does not cite CDC); IARC Group 1 carcinogen designation for nickel (paper does not cite IARC); 10-30 year cadmium kidney half-life (not in paper); β2-microglobulin and retinol-binding protein as cadmium nephropathy biomarkers (not in paper); AS3MT enzyme name plus folate/B12 nutritional modifiers for arsenic methylation (paper figure shows pathway without naming AS3MT or invoking nutritional cofactors); reduced IQ / motor dysfunction / language delay specifics for MeHg neurodevelopment (paper states neurotoxic mechanisms only, not specific outcomes); Minamata anchor case (not in paper); nickel dermatitis as best-established human effect (paper focuses on oxidative-stress mechanisms, does not discuss allergic contact dermatitis); specific food list (whole grains, legumes, nuts, chocolate) for nickel exposure (paper says only “food” generically). Added Key numbers section with the quantitative claims fu2019 actually carries (140M / 35-77M / 75 ppb Warburg / 900 occupations / GSH:GSSG 90:10) per the source page template. Updated raw_handle from legacy papers-cube placeholder to PCMF_fu2019 convention. Frontmatter products/ingredients/jurisdictions remain empty: this is a mechanism review with no measured foods, ingredients, or jurisdiction-specific regulatory analysis; the routing_malformed advisory for those fields is informational, not a defect.
• 2026-05-17 (prior session): Cross-vendor strict Part 12 recheck found no sampled-product brand naming. Added MeHg to the metal scope, removed a non-taxonomy health wikilink, converted generic arsenic/mercury wikilinks to speciated metal pages, and tightened the limitations/courses language to avoid cross-source synthesis.

Page history

The five most recent substantive edits to this page. 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.