The Chemical Inertness of Pure Metallic Gold
Metallic gold, especially in its pure form (24-karat), is known as a 'noble metal' due to its low chemical reactivity. Unlike other heavy metals such as lead or mercury, which can react with stomach acid and form toxic compounds, pure gold remains unreactive within the human body. When ingested, for example as edible gold leaf used to decorate food, it will pass through the digestive system entirely unchanged. It offers no nutritional value, no health benefits, and will be eliminated from the body as waste. This is why edible gold, when guaranteed to be of high purity (23–24 karats), is considered safe for consumption.
How Pure Gold Interacts with the Body
- Ingestion: As mentioned, pure gold leaf or flakes are not absorbed by the digestive tract. They simply pass through. If the gold is alloyed with other metals, like copper, those other metals could be absorbed and become toxic if consumed in high enough quantities.
- Jewelry and Skin Contact: The friction from wearing gold jewelry can theoretically wear it down into nanoparticles that could pass through the skin, though there is little evidence this happens significantly or causes noticeable discoloration. High-karat gold is generally considered biocompatible and safe for skin contact.
- Implants and Dentistry: Gold alloys have been used for centuries in dental work due to their biocompatibility and corrosion resistance. The gold does not break down, which prevents adverse reactions. In other applications like pacemakers or stents, gold plating is used for its reliable, non-reactive nature.
The Breakdown of Gold Nanoparticles and Compounds
In contrast to pure, solid gold, the body can metabolize and degrade gold in its more reactive forms, such as gold nanoparticles (GNPs) or ionic gold compounds (gold salts). This behavior is fundamental to their use in medicine, a practice known as chrysotherapy.
Medical Uses and Metabolic Fate
- Chrysotherapy: Since the 1930s, specific gold salts like gold sodium thiomalate have been used to treat conditions like rheumatoid arthritis. These compounds are administered by injection and are absorbed into the body, where they accumulate in organs of the reticuloendothelial system like the lymph nodes, liver, and spleen. The anti-inflammatory effect is linked to gold ions released from the compound.
- Nanomedicine: Gold nanoparticles are increasingly used in diagnostics and cancer therapy due to their unique optical and chemical properties. Recent studies have shown that contrary to past assumptions, GNPs are not entirely inert once inside cells. In fact, they undergo intracellular biodegradation and recrystallization in the lysosomes of macrophages and fibroblasts. The smallest nanoparticles degrade fastest, and the resulting biomineralized gold can resemble structures observed in patients treated with gold salts.
The Body’s Response to Gold Breakdown
The metabolism of gold compounds and nanoparticles is a complex, multi-stage process:
- Distribution: Upon injection, gold compounds are distributed via the bloodstream and accumulate in the reticuloendothelial system. For nanoparticles, their size, shape, and coating influence where they end up, but the liver and spleen are common destinations.
- Cellular Uptake: Phagocytic cells like macrophages internalize nanoparticles, sequestering them inside lysosomes.
- Degradation: Within the acidic environment of the lysosomes, enzymes facilitate the biodegradation of the gold, causing it to change its form.
- Excretion: Over time, gold from medical treatments is excreted primarily through feces and urine. However, some gold deposits can remain in tissues for years after treatment has ended.
Comparison of Metallic vs. Nanoparticle Gold in the Body
| Feature | Pure Metallic Gold (Edible Leaf/Dental) | Gold Nanoparticles/Compounds (Medical) |
|---|---|---|
| Chemical Reactivity | Chemically inert; does not react with bodily fluids. | Metabolically active; converted into ionic forms. |
| Absorption | Not absorbed by the body; passes through digestive system. | Absorbed and distributed through the bloodstream. |
| Breakdown | Does not break down in the body. | Undergoes intracellular degradation and recrystallization. |
| Health Effect | No nutritional value or benefits. Safe for consumption in high-carat forms. | Used therapeutically (e.g., for arthritis, cancer) but can cause side effects at high doses. |
| Biodistribution | Not distributed. Ingested gold is excreted. | Accumulates primarily in organs like the liver, spleen, and lymph nodes. |
| Long-Term Fate | Expelled from the body completely. | Can leave behind long-lasting residual deposits, such as aurosomes. |
Conclusion
Contrary to the simple idea that "gold is gold," its fate in the human body is critically dependent on its physical and chemical form. Pure, bulk metallic gold, such as in jewelry or edible foil, is chemically inert and passes through the body without being absorbed or broken down. This biological inertness is what makes it safe for consumption and use in dental work. However, modern medical science has shown that when gold is introduced in different forms, such as gold nanoparticles or specific gold salts, it is metabolically active. These more reactive forms are taken up by cells, where they are degraded and distributed, leaving behind long-lasting deposits in tissues. Understanding this distinction is crucial for evaluating the safety and therapeutic applications of gold in medicine and consumer products. Learn more about the history and medical uses of gold from the National Institutes of Health.
Frequently Asked Questions
Q: What happens if you eat a piece of pure gold jewelry? A: Swallowing a piece of pure gold jewelry is not advisable. While pure gold is inert and would not chemically break down, the dense, solid metal could pose a physical danger such as causing choking or internal damage as it passes through the digestive tract.
Q: Is edible gold digested by the body? A: No, high-carat edible gold is not digested. It is chemically inert, meaning it doesn't react with the body's digestive acids or enzymes and therefore passes through your system entirely unchanged.
Q: Why are some forms of gold toxic while others are not? A: The toxicity of gold depends on its chemical state. Pure elemental gold is non-toxic because it does not react with the body. However, gold compounds (gold salts), especially in high concentrations, can be toxic and are absorbed by the body, as they are not inert.
Q: What is chrysotherapy and how does it use gold? A: Chrysotherapy is the therapeutic use of gold compounds, typically in the form of gold salts, to treat certain medical conditions. It was historically used to treat rheumatoid arthritis by injection, where the gold compounds act as anti-inflammatory agents within the body after being metabolized.
Q: Can gold nanoparticles be eliminated from the body? A: Yes, while some gold nanoparticles can accumulate in organs, studies have shown that they undergo degradation and their components can be eliminated over time through bodily processes like excretion, though some residual deposits may remain for many years.
Q: Do gold implants, like dental fillings, break down over time? A: No, the gold alloys used in medical implants and dentistry are chosen for their excellent biocompatibility and high resistance to corrosion. They are designed to be stable and not break down in the body over a long period.
Q: What are aurosomes? A: Aurosomes are microscopic, gold-containing deposits that can accumulate inside the lysosomes of cells, such as macrophages, following exposure to gold compounds or nanoparticles. They can persist in the body for long periods, sometimes for years after treatment has ended.
