Heavy metals are a natural part of the Earth and the surrounding atmosphere, but industry and pollution from humans have hugely increased the number of heavy metals in the soil, air, and water.
Making global headlines, the most recent first world heavy metal contamination occurred in Flint, Michigan, in 2014 (1), when an estimated 6,000-12,000 children were exposed to lead-contaminated drinking water.
Some of the foods we eat are high in heavy metal contamination because of the food chain (for example, fish living in pollution-contaminated waters near industrial sites are higher in heavy metals).
This list covers some of the foods that are highest in heavy metal contamination and should be eaten in moderation and with care (particularly to where they are harvested from).
What foods are high in heavy metals?
1. Fish
Fish are a notorious source of heavy metal contamination, particularly mercury. Runoff from industrial sites and pollution within fish’s food chain leads to a buildup of mercury and other toxins, which can pose a health risk to humans.
In a recent study done in Sicily, fish caught from areas near petrochemical industrial areas had higher levels of cadmium, lead, mercury, and chromium in their muscle tissue than fish caught in other areas (2). While these levels were low enough that they weren’t an immediate carcinogenic (cancer) risk to humans, no amount of heavy metals is a good thing in our food.
The Yangtze River in China is one of the most polluted bodies of water in the world, having multiple industrial factories (and their associated runoff) poised very close to the river banks. Fish caught along the Yangtze have high levels of chromium, cadmium, mercury, copper, zinc, and iron, and eating them can pose a health risk, depending on how much fish is consumed (3).
2. Brown rice
Unfortunately, this superfood (see our “World’s Healthiest Rice Varieties” article) has a secret. Soil contaminated with heavy metals from wastewater-irrigation has resulted in contaminated brown rice.
At elevated risk are populations living near mining sites or other industries where wastewater works its way into agricultural soil. Studies on at-risk sites like these showed high levels of lead, cadmium, arsenic, manganese, and antimony in brown rice samples grown locally(4).
In controlled models, heavy metal quantities of brown rice don’t seem to exceed the “safe” limits of heavy metals (5). Still, continuous monitoring of the amount of wastewater reaching crops and overall soil health is necessary to keep surrounding populations safe.
3. Leafy green vegetables (Oh no!)
Oh, yes. Our best diet friends, the superheroes of health, have had some heavy metal contamination in the recent past.
Soil contaminated with industrial runoff or nearby air pollution has led to elevated levels of cadmium, zinc, copper, iron, chromium, and iron (in the order, from highest to lowest levels detected) (6). The contaminant nickel was also found in leafy greens when Sri Lanken samples were analyzed (7).
It’s important to know where your leafy greens have come from, and whether or not they were harvested near an industrial center or polluted area.
4. Vegetable oil
I’m sure this is not something you were expecting on this list, but this is a heavy metal–contaminated food item that has concerned health officials in the past (8).
In a study performed in China, several vegetable oils sold for human consumption were found to contain trace amounts of copper, zinc, iron, manganese, cadmium, nickel, lead, and arsenic (another reason to limit consumption of oil in your diet) (9). However, the estimated intake was thought to be low enough that these did not pose an immediate risk to human health.
5. Food coloring
This includes “natural color” on the ingredient list. In a Tokyo study examining a variety of food additives and colors, 8 of the 40 tested had some level of heavy metal (lead, cadmium, or mercury) (9).
Several of these samples exceeded the safe limits for these heavy metals, and to prevent future problems, more studies are needed in this area to determine why and how this contamination occurred.
6. Bone broth
This particular item is near the end of our list because the heavy metal content doesn’t necessarily make the food bad for you. Bone broth has been found to contain several heavy metals including mercury and copper, and these levels increase the longer the bones are boiled (10).
This is because animal bodies (ours, too!) sequester heavy metals in the bones. But, studies have shown these levels are extremely low, and well within the safe zone (11). Take this as a friendly reminder to keep your diet versatile, and not overdo a good thing.
Particularly for vulnerable populations that are recommended to increase consumption of bone broth (this diet is recommended for a myriad of conditions including depression, schizophrenia, Paleolithic diets, or ADHD (12)), it should be taken with other foods and in moderation.
7. Unfiltered water
Many of us in the first world take our clean drinking water for granted. This is near the end of our list because, while it’s not technically a food, heavy metal contamination of drinking water (like the Flint Water Crisis mentioned in the introduction) is a very real problem for much of the world.
In addition to contamination from natural sources, heavy metals in water come from agriculture (fertilizers, manure, pesticides), sewage contamination, energy production (gasoline, batteries, and power plants), and scrap disposal (13). In fact, the United States has had several problems with heavy metal contamination with copper and lead, which are not necessarily correlated with low household income status (14).
8. E-cigarettes
This makes our list of heavy metal “foods” because e-cigarettes are now widely consumed around the world, and have continued to gain popularity since their introduction in 2003. As a rule, part of a healthy diet and fitness regime means the only thing going into your lungs should be clean air.
Because e-cigarette vapor contains a variety of chemicals (including heavy metals), it isn’t harmless. In fact, when tested, 56 e-cigarettes were found to contain toxic chromium, nickel, and lead (15), all of which can be carcinogenic (cancer-causing) (16).
Where do the most prevalent heavy metal contaminants come from?
Arsenic is linked with diabetes, lung cancer, and cardiovascular disease, and is typically consumed in drinking water. Industrial contamination is the most likely source of arsenic, in addition to agricultural fertilizers and pesticides, and cigarette smoke (17). Arsenic is tasteless and odorless, and therefore impossible to detect before consumption.
Mercury contamination is prevalent in shellfish and aquatic life. Mercury enters aquatic systems primarily through atmospheric deposition, erosion, urban discharges, agricultural materials, mining, and combustion and industrial discharge (18).
Essentially, a mixture of natural deposits, industrial complications, and mining (which increases the natural abundance of mercury in specific locations and contributes to mercury levels through runoff) increase mercury contamination.
Take a look at our article “What is the Healthiest Seafood?: From Sustainability to Health” to see what seafoods are low in heavy metals and healthy to eat.
Copper has been used in electrical wires, utensils, and piping, and has become a significant environmental contaminant in drinking water. Sources of copper in water typically include mining, erosion, sewage treatment plants, antifouling paints, and industrial runoff into freshwater (19).
Copper is known to cause kidney, heart, liver, stomach, and brain problems when ingested in toxic doses.
Nickel was originally praised for being a corrosion-resistant metal, but has toxic effects on the nervous system, heart, and liver.
While it is naturally found in volcanic eruptions and atmospheric dust, contaminant levels of Nickel in water and soil are vastly increased by mining and smelting nickel ores, manufacturing stainless steel, and industrial fossil fuel combustion and incineration.
Cadmium is a heavy metal that accumulates in our bodies, and becomes carcinogenic. Used as a paint and tin substitute, in rechargeable batteries, and in tobacco, cadmium is found in a variety of everyday items. Sources include pesticide residues, cigarette smoke, industrial runoff, and pollution (20).
In Taiwan, a rice crop contamination was found to originate from a cadmium factory that had been releasing runoff into the surrounding water and field space, contaminating the crop (21).
Chromium naturally comes from continental dust, but has become a problem due to its industrial use. Fossil fuel consumption, electroplating, leather tanning, and textile manufacturing all release chromium pollution into the environment (22).
These increases affect both human health and marine life (23) (which comes back to us through the food chain). Chromium poisoning leads to the gastrointestinal, nervous system, and skin problems over time (24).
Iron has traditionally been used to manufacture steel, reinforce concrete, and make other architectural and building components (like pipes). Iron is a healthy and essential nutrient for our bodies (25), but when it accumulates, toxic levels cause “iron poisoning.”.
Iron poisoning has a variety of symptoms, including gastrointestinal distress, vomiting, impaired consciousness, and convulsions (26).
Aluminum poisonings often occur from exposure to aluminum phosphide (27), which is an insecticide and rodenticide (28). Although many mild forms of aluminum (such as antiperspirant and aluminum foil) are used frequently without health complications, some compounds of aluminum can lead to poisoning.
Over-exposure to aluminum is thought to cause neurodegenerative disease (29), but this is still being investigated. Being aware of your aluminum use and intake and limiting aluminum exposure when possible (e.g., purchasing deodorant without aluminum) is an excellent first step.
Lead may be one of the most widely publicized heavy metal contaminants in the first world. Lead has been used as a corrosion-resistant metal in cable sheathing, circuit boards, chemical pipes, radiation shielding, and pipes (30). Lead is also a constituent of car exhaust, gasoline, old paint, and fertilizers (31).
We now know that lead exposure can cause harm to reproductive organs, kidneys, the gastrointestinal tract, and the brain.
Could chelation therapy reduce the effects of heavy metal ingestion?
Chelation means “bind,” so this treatment for heavy metal poisoning works by using a compound called edetate disodium (EDTA) that can bind up heavy metals in the blood and carry them out of the body (32).
However, this is only useful for blood poisoning. If the heavy metals have entered the brain, then chelation therapy is not effective. This therapy is still undergoing trials and is not currently actively recommended as initial therapy. Side-effects include headaches, blood pressure decrease, permanent kidney damage, and calcium level reduction.
In conclusion
It’s important to be aware of your surroundings and places where you may be getting more heavy metals than you bargained for. From deodorant to fish to pipes, these health-damaging compounds are hiding in many commonplace items.
It’s up to you to be aware of what you purchase and where it is from, and minimize your heavy metal exposure wherever possible.