Heavy metals are naturally-occurring metallic elements that have an atomic weight greater than or equal to a certain threshold. This threshold varies depending on the author and source, thus making the term “heavy metal” ambiguous.
In the context of Physics, “heavy” might be an attribute assigned based on atomic weight. In metallurgy, “heavy” might be more associated with an element’s density. In Biology, “heavy” might be a relative function towards another compound, such as water. So what does “heavy metal” actually mean in the context of your health?
- There is no consensus for the definition of “heavy metal”
- Many “metals” can be beneficial or harmful
- Many researchers use the terms “heavy metals” and “potentially toxic compounds” in a statistically-interchangeable way.
- One can have trace levels of “toxic” compounds without issue.
- Heavy metal chelation supplements, protocols, and diets might remove beneficial compounds.
Toxicological research commonly uses the term “heavy metals” to describe compounds that represent potential harm both to biological organisms and the environment. Again, the ambiguity of “heavy metals” is characterized further such that it’s also unclear what constitutes a “toxic” heavy metal.
Many compounds that are common to human studies on toxicological damage— such as lead, cadmium, and mercury—are found naturally in the Earth’s crust. These elements are found in trace amounts within food supplies, much like vitamins and other phytonutrients. To understand how these elements may influence health, let’s try to work out what metal is, what might make it heavy, and if it’s thusly toxic.
What are Metals?
Metals are elements that can conduct electricity, are malleable, are ductile, form cations, bind to other compounds through oxidative processes, and show visible luster.
By this definition, it’s clear that many elements—both “toxic” and “non-toxic”—can be considered metal. This partially illustrates the difficulty in making a statement such as “iron, magnesium, and selenium are good for health but mercury, lead, and cadmium are bad.” After all, they all meet the above criteria to be considered “metal”—at least to some degree.
What are “Heavy” Metals?
In a 2009 paper, John H. Duffus of the Edinburgh Centre for Toxicology composed an exhaustive survey of how the term “heavy metal” was being used by researchers. He found very little consistency. Below are some of the varying characteristic thresholds of “heavy metals” he found in his study:
Density-Related Thresholds (g/cm3)
- Density > 7
- Density > 4
- Density > 5
- Density > 6
- Density > 3.5-5
Atomic-Weight Related Thresholds (Mass)
- “high” atomic weight
- Weight > sodium
- Weight > 40, but Excluding Alkaline Metals
- Metal with “high” atomic mass
- Metals such as lead, cadmium, and mercury
- High relative mass, including copper, lead, or zinc
Atomic Number Related Thresholds
- Moderate to High atomic numbers such as Copper, Zinc, Nickel, and Lead
- Rectangular block on the periodic table “flanked” by titanium, hafnium, and bismuth
- Any metal with an atomic number > calcium
- Any element with an atomic number > 20
- Metal with an atomic number between 21 and 92
Duffus outlines several other criteria of which he found other researchers to use in their definitions of “heavy” metals. These additional criteria only serve to deepen the ambiguity. The only thing clear is that there is no clear definition of “heavy” in the context of elemental elements. The term “heavy metals” is so ambiguous that it’s been described as a geochemical “bogey man” by researchers pushing for more precise terminology.
What are “Toxic” Heavy Metals
Certain compounds such as Zinc, Copper, and Manganese are known beneficiaries of human health. These elements help support critical biological functions in the human body, so much so they are sold as dietary supplements. Still, in high amounts, even these beneficial compounds can become toxic.
Other elements such as Mercury, lead, cadmium, and arsenic are much likelier to represent toxicological threats both to environmental health and biological health. At least measured by frequency of discussion within toxicological research.
In a 2019 paper, researchers presented a case to replace the term “heavy metal” with “Potentially Toxic Elements.” While stating their case, they presented two tables of data illustrating the frequency certain elements were mentioned as being “Heavy Metals” compared to the frequency they were mentioned as being a “Potentially Toxic Element.”
“Heavy Metal” Mentions (996 total)
|Element||% of Mentions|
“Potentially Toxic Element” Mentions (131 Total)
|Element||% of Mentions|
The takeaway here, and what I believe was a primary point being made by researchers, is that the term “heavy metal” is often used to mean “potentially toxic element.” The elements line up nearly identically, save that Cobalt is mentioned within the context of potential toxicity, and iron is not. For clarity—Iron can absolutely be toxic. I believe the above analysis was meant to be a purely statistical representation of the interchangeability between the two terms.
It’s clear that the term “heavy metals” is, at best, ambiguous and, at worst, misleading. Certain elements such as Manganese, Iron, or Selenium may fall within criteria to be labeled as “heavy” by researchers. I believe this ambiguity poses a threat to human health, illustrated by the many numbers of “heavy metal” chelation protocols, dietary supplements, and warnings I’ve seen over the years.
For example, many chelators such as EDTA can remove many elements. While doing a “heavy metal cleanse” one might mop up some extra mercury but inadvertently cause a zinc deficiency. Supplementing with Zinc could help, but might also cause a copper deficiency to arise. The subject of eliminating potentially toxic metals from the body is a complex subject.
Knowing whether your levels of “heavy metals” are actually toxic is essential. A heavy metals hair test is among the best medical tests I’ve ever had. The results can be difficult to interpret and I encourage anyone considering such a test to work with an experienced practitioner. Sometimes heavy metal toxicity can actually be a paradoxical symptom of deficiency. I can’t imagine sorting that out on my own.