From Soil to Plate: Health Implications of Heavy Metals in Your Food

Ideally, everything we consume in our lives would be all-natural and free of impurities. However, in practice, there is nothing 100% pure in nature. Everything that enters our body has some contaminants or impurities. Some of these impurities are toxic to the body, including heavy metals in foods.

Heavy metal exposure, even in small amounts, can harm our health in many ways such as increasing the risk of cancer and organ damage. Interestingly, heavy metals enter the human body in minute amounts on a daily basis. They enter the body via water, food, medications, health supplements, air inhalation, and even via the skin. Thus, it is vital to know what heavy metals are, the health risks associated with them, and their maximum tolerable limits.

Talking about heavy metals can be tricky, so it’s important to start by understanding what they are. There isn’t a universally agreed-upon definition for heavy metals, but they are most commonly defined as metals with a relatively high atomic mass. Surprisingly, even iron falls into this category based on this definition.[1,2] In contrast, we’ve also heard about how essential iron is in our diet. On the other hand, there are metals like aluminium that might cause toxicity when ingested in very high amounts.[3] Aluminium is present even in some medications like antacids, which might confuse the average consumer. Chromium is another example of a metal that is toxic in excess but required in trace amounts.[4] This is where a lot of confusion about heavy metals arises from.

However, in the context of foods/health, the definition of heavy metals differs from that in chemistry. In the context of health, it would be right to consider those metals as “heavy metals” that are toxic, such as lead, arsenic, cadmium & mercury.[2] Ideally, everything we inhale or ingest should be free from these particular toxic metals. They have no nutritional value and are harmful even in minute amounts.

The two primary ways that heavy metals enter the human body are inhalation and food. Toxic metals like arsenic, lead, cadmium, and mercury are commonly present in various foods like fruits, vegetables, animal meat, and fish.[6]

The primary reason for higher exposure to heavy metals is industrialization. In the pre-industrial era, the only source of heavy metals was the minute amounts found in the soil. Since the beginning of the industrial age, humans have started extracting heavy metals on a massive scale. Thus, the production of heavy metals has increased by several hundred times since the 18th century.[2]

Of course, humans were using some heavy metals, like lead or mercury, even before the industrial age, but their production was very low in the pre-industrial era.

Arsenic, for example, is naturally present in the soil in tiny amounts. However, increased soil erosion also increases its concentration in the soil. Arsenic is also present in some insecticides and pesticides.[7]

Lead is another commonly found heavy metal contaminant, due to its extensive use in industry. Burning of fuels also releases lead in minute amounts into the air. Thus, foods grown near highways are more likely to be contaminated with lead. Lead is also present in batteries and, most concerningly, small amounts are present in fertilisers and pesticides, leading to an increase in soil concentration levels.[2]

Mercury exists in the soil in small quantities and was historically utilised by certain industries. However, there’s good news—its industrial usage is decreasing worldwide. Mercury is no longer incorporated into paints and pesticides, contributing to a decline in its overall presence in these products.[7]

DNA Damage and Cancer Risk

Heavy metals, even in tiny doses, pose significant genetic harm. High exposure can damage DNA, heightening the risk of various cancers.[5]

Interference with Cellular Functions

Heavy metals interact with cellular enzymes and signalling molecules that are crucial for cellular communication. Even small amounts can disrupt essential mechanisms due to the minute presence of these molecules.

Disruption of Biological Processes

Heavy metals can also lead to disruptions in tissue growth and regeneration, increased inflammation, oxidative stress, and heightened production of reactive oxygen species.[5]

Other Health Concerns

Heavy metal contamination may also result in common health issues such as cancer, fatigue, and weakened immunity. Certain heavy metals specifically target and damage particular organs, necessitating focused attention and care.

Although the full list of heavy metals can be quite long, we will look at the harmful effects of four heavy metals posing the greatest health risks. These metals are widely used in industry; thus, they are among the most significant soil pollutants and are more likely to enter the food supply chain.

Arsenic

Arsenic exposure in South Asia, including India, is exceptionally high due to groundwater contamination. It can inactivate more than 200 enzymes in the body.[7] Low-level exposure to the metal can cause vomiting, reduced red cell production, changes in heart rhythm, and damage to blood vessels. Arsenic can even cause death due to acute poisoning at higher exposure.[8]

Like all heavy metals, it can cause cancers. However, it is especially bad for heart health. It can cause heart disease and damage blood vessels. Arsenic damages blood vessels and interferes with neurotransmitters, impacting brain communication.[5] Skin and hair damage (thus hair fall) are common due to chronic exposure. It can also cause brain damage, intestinal discomfort, and liver damage.[5]

Lead

Lead is the most commonly used heavy metal. Lead acid batteries are also the most common types of batteries used in India (vehicles, home power backup), and can also be found in paints, pigments, and metal sheets. Hence, it readily makes its way to groundwater and soil, and thus the food.[7]

Lead is toxic to most organs. Thus, it can cause brain damage, lung injury, stomach colic, liver damage, and heart disease. It is also associated with declining sperm count.[5,8] Lead causes severe inflammation and hinders the synthesis of haemoglobin, affecting blood function.[5]

Cadmium

While cadmium is relatively rare in soils, it may make its way into the soil through certain industrial activities. It is also a highly carcinogenic (cancer-causing) heavy metal.[5]

Cadmium exposure harms bones, kidneys, liver, lungs, and intestines, while also disrupting the metabolism of zinc and copper in the body.[5] 

Mercury

Mercury was very commonly used in different industries, including traditional medicine in India, like in some Ayurvedic and Siddha remedies. However, today its use is quite uncommon as relatively safer remedies are available.[9] Mercury is still widely used in various industries and thus, still present in food in traces.[7]

In recent years, there’s been significant concern regarding increasing mercury levels in fish. This rise is linked to industrial waste finding its way into the sea. Because many seafish have longer lifespans, they tend to accumulate higher amounts of mercury over time.[7]

High mercury exposure can also permanently damage the brain and kidneys and cause liver toxicity.[5,8] Mercury is also known to inhibit enzymes and significantly induce oxidative stress, affecting cellular functions and health.[5]

Heavy metals tend to accumulate in our bodies as we struggle to purge them effectively. Even in small amounts, they can be detrimental to our health. 

The Food and Drug Administration (FDA) in the US stipulates that heavy metal content in medications and supplements should ideally range from one to ten parts per million(ppm).[10]

While medications undergo strict testing for heavy metal content, the same doesn’t always apply to foods and health supplements. Though there are guidelines regarding the maximum permissible levels of heavy metals in foods, they are challenging to enforce. Consequently, most foods in the market are never tested for heavy metal content.

Research indicates that small amounts of heavy metals exist in commonly consumed foods like fish, meat, beans, vegetables, and fruits due to their natural presence. However, the concern arises when they exceed permissible amounts.[6]

In India, FSSAI (Food Safety and Standards Authority of India) maintains a permissible heavy metal contamination list. It first created a comprehensive document in 2011 and then revised it multiple times. The latest revision was done in 2020.[11–13]

FSSAI’s list is quite comprehensive. It not only covers heavy metals but also permissible limits of most contaminants of significant concern. Additionally, it describes the permissible limits of specific heavy metals in different foods, supplements, and food additives. You can read this FSSAI document here.[11]

Here are some of the heavy metal limits set forth by FSSAI for various categories:[12]

• Lead: 0.3 ppm (parts per million) in leafy green vegetables, 0.1 ppm in bulb, root, tuber, and fruit vegetables (e.g. Tomato, potato, cauliflower, orca, and so on).
• Arsenic: 0.1 ppm in milk,  1.1 ppm in vegetables and most other foods.
• Cadmium: 0.4 ppm in polished rice, 0.05 ppm in bulb and fruiting vegetables, and 0.2 ppm in leafy veggies.
• Mercury: No more than 0.5 ppm in fish, but a higher amount of 1.0 ppm is allowed for predatory or large fish varieties (generally sea fish) like tuna, marlin, swordfish, and others.

Though many people know about the harmful effects of pesticides and insecticides in foods, there is far less awareness about heavy metals in foods, food additives, and food supplements. Even for those of us who may be aware of the adverse health consequences of heavy metal contamination, identifying which food products to consume and which ones to avoid can be a huge challenge.

In recent years, FSSAI has taken several steps to ensure consumer safety. However, there is still much to be done. For practical reasons, many packaged food products and health supplements remain untested for heavy metals. Most people, however, can reduce their risk of heavy metals exposure by carefully inspecting the food labels as well as going the extra mile and conducting some research.

Unbox Health makes that process a lot easier by lab-testing packaged foods and health supplements in the market and rating them based on FSSAI safety guidelines.

[1] Duffus by JH. “Heavy Metals”–A Meaningless Term. Chemistry International — Newsmagazine for IUPAC. 2001;23:163–167.

[2] Jaishankar M, Tseten T, Anbalagan N, et al. Toxicity, mechanism and health effects of some heavy metals. Interdiscip Toxicol. 2014;7:60–72.

[3] Aluminium in Food (Q&A): sources, safety and regulations [Internet]. [cited 2023 Oct 26]. Available from: https://www.eufic.org/en/food-safety/article/aluminium-qa.

[4] Anderson RA. Chromium as an essential nutrient for humans. Regul Toxicol Pharmacol. 1997;26:S35-41.

[5] Balali-Mood M, Naseri K, Tahergorabi Z, et al. Toxic Mechanisms of Five Heavy Metals: Mercury, Lead, Chromium, Cadmium, and Arsenic. Front Pharmacol. 2021;12:643972.

[6] Liang G, Gong W, Li B, et al. Analysis of Heavy Metals in Foodstuffs and an Assessment of the Health Risks to the General Public via Consumption in Beijing, China. Int J Environ Res Public Health. 2019;16:909.

[7] Tchounwou PB, Yedjou CG, Patlolla AK, et al. Heavy Metals Toxicity and the Environment. EXS. 2012;101:133–164.

[8] Center for Hazardous Substance Research, Kansas Stat University. Human Health Effects of Heavy Metals [Internet]. [cited 2023 Oct 26]. Available from: https://engg.k-state.edu/chsr/files/chsr/outreach-resources/15HumanHealthEffectsofHeavyMetals.pdf.

[9] Abdalla AA, Smith RE. Determination of Mercury in Ayurvedic Dietary Supplements That Are Not Rasa Shastra Using the Hydra-C Direct Mercury Analyzer. Int J Anal Chem. 2013;2013:628397.

[10] CFR – Code of Federal Regulations Title 21 [Internet]. [cited 2023 Oct 26]. Available from: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=172&showFR=1.

[11] fssai. Fssai – FOOD SAFETY AND STANDARDS (CONTAMINANTS, TOXINS AND RESIDUES) REGULATIONS, 2011, Version –V (19.08.2020) [Internet]. 2020 [cited 2023 Oct 26]. Available from: https://www.fssai.gov.in/upload/uploadfiles/files/Compendium_Contaminants_Regulations_20_08_2020.pdf.

[12] fssai. Fssai-Metal Contaminants in Foods – Potential Risk and Mitigation Measure (Guidance Note No. 15/2020) [Internet]. [cited 2023 Oct 26]. Available from: https://fssai.gov.in/upload/uploadfiles/files/Guidance_Note_Metal_13_03_2020.pdf.

[13] India Amends its Food Safety and Standards (Contaminants, Toxins and Residues) Regulations [Internet]. SGSCorp. [cited 2023 Oct 26]. Available from: https://www.sgs.com/en-in/news/2020/11/safeguards-16720-india-amends-its-food-safety-and-standards-contaminants-toxins.