What are heavy metals?

Heavy metals are heavy elements. While some essential elements, such as zinc and iron, are technically heavy, the heavy metals that are of concern are elements that serve no biological function and pose a threat to health. Arsenic, cadmium, lead, and mercury are the heavy metals that pose the greatest threats to public health, and, incidentally, are all on the World Health Organization’s (WHO) top 10 chemicals of public concern.¹ Even though they are naturally occurring and found throughout the earth’s crust, human exposure to heavy metals that causes problems is mostly due to human activities like mining, smelting, industrial production, pesticides, etc.²

Are heavy metals bad for us?

Yes. Heavy metals can produce health risks when we are acutely exposed to high levels, as in the workplace, which usually leads to severe and rapid onset of symptoms. Chronic low exposure over a long period of time can result in accumulation that poses a health risk too, but the symptoms may be more subtle. Each heavy metal comes with its own unique health risks, but they all have similar mechanisms of action for inducing toxicity, which involve the generation of free radicals and weakening of our own antioxidant defenses, leading to oxidative damage in a variety of tissues and organs.³ Heavy metal toxicity can cause digestive dysfunction, kidney dysfunction, nervous system disorders, skin lesions, vascular damage, immune system dysfunction, birth defects, and cancer.³

How am I being exposed to heavy metals?

Heavy metals are in our air, water, and soil. They may also be found in the materials used to build our homes, the products we use, and sometimes our workplaces. They used to be found in common products such as paint and gasoline, which have left their mark on our environment today too. And because they are so ubiquitous in our environment, they are in our food. Foods can come in contact with heavy metals in a variety of ways. Heavy metals can fall onto food as it grows; they can be taken up by foods from the soil; they can contaminate the water used on crops; they may be in pesticides, fertilizers, or sewage sludge applied to non-organic food crops; and they may be present in some processing steps, packaging, or transport. In many foods, the concentration of heavy metals is very small, but in some foods it can be much higher.

Is anyone monitoring and setting limits for heavy metals in our foods?

Yes. The US Food and Drug Administration (FDA) does monitor the food supply and has set limits for heavy metals in many foods likely to be contaminated and/or consumed by high-risk groups (such as infants and children), although their guidance is limited beyond that. Similarly, the European Union and WHO have their own safety limits. California Proposition 65 (Prop 65) has also established “safe harbor” levels for heavy metals and requires warning labels on any products that contain heavy metals (and other substances) at or above those levels. Although the warnings are legally required only for products sold in the state of California, many companies print one label for the entire United States, so consumers across the country may see these warnings. Proposition 65 (Prop 65) limits are the strictest of the regulations.

Should I be concerned?

For most people, mild exposure to toxic heavy metals is not a health risk, because our bodies are capable of clearing these toxins. However, heavy metals can be dangerous, especially when the load in our bodies exceeds our capacity to clear them, and this can vary greatly from person to person. Children (including in utero and when nursing) are probably the most vulnerable population because children’s small bodies, slower metabolism, and rapid growth rates make them more susceptible to heavy metals’ effects. Exposure to heavy metals during active brain development is associated with learning and behavioral disabilities and lower IQ, in addition to other physiological effects.⁴ To know whether you should be concerned about heavy metal exposure, consider your general level of health, your age (older people tend to have accumulated higher levels than young people and may have reduced detoxification capabilities), and all the ways you might be exposed to heavy metals (including where you work, the air quality where you live, your water, your use of heavy metal-containing cosmetics or other chemicals, etc.).

But what about all the news reports?

Take sensational news reports with a grain of sea salt. The science around heavy metals can be confusing, and over the years, misleading reporting has introduced some significant flaws that have complicated the issue. For example, a Consumer Report article from 2022, as well as a July 2024 study published in Frontiers in Nutrition, tested cocoa products, particularly dark chocolate bars, and reported that many exceeded allowable limits for lead and cadmium.^{6 7} Both studies relied on the Prop 65 maximum allowable dose levels (MADLs), instead of the more recent and scientifically validated numbers established for cocoa and chocolate products

An MADL is determined by taking the highest level of heavy metal where there would be “no observable effect or harm to humans or laboratory animals” when eaten at one serving per day and dividing it by 1,000 to provide an additional margin of safety. Because the calculation of MADLs is based on the amount of a chemical that is without significant risk of causing harm, MADLs yield a very large margin of safety and reflect an immense abundance of caution. In fact, MADLs are set so low that most cocoa and dark chocolate cannot be below these levels due to the natural presence of heavy metals in the environment. In 2018, a California state court agreed with this, passing a consent judgement that legally set more reasonable levels for cadmium and lead in cocoa and chocolate products, which superseded the general Prop 65 MADLs and are more in line with international standards. Based on these updated and scientifically valid thresholds, most products tested in the studies fell within these limits. Additionally, as the 2024 study noted, nearly all products tested (70 of 72) fell below FDA limits for lead. While the FDA limit is higher than the general Prop 65 MADL for lead, it still provides an appropriate benchmark for safety, as it is calculated with a 10x safety factor, meaning it is one tenth of the amount of lead intake from food that would be required to reach a blood level of lead in which clinical monitoring is recommended.

At Natural Grocers, all chocolate bars, cocoa powders and nibs, and dark chocolate chips comply with the Prop 65 safety limits, as amended in 2018 by a California state court judgement, as well as the U.S. Food & Drug Administration (FDA) safety limits and European Union Safety Limits. You can feel confident that these products are safe and that we jointly work with our suppliers and manufacturers to monitor the naturally occurring trace amounts of heavy metals in at-risk products to comply with all safety standards. Additionally, while the 2024 study did report that organic cocoa products were more likely to have higher levels of cadmium and lead, this was a marginal difference and should be considered in context with the numerous benefits of choosing organic, particularly reducing our exposure to synthetic pesticide residues, in addition to supporting environmentally sustainable farming practices and the health and well-being of farm workers.

Another issue that is commonly confused in the public is differentiating between the different forms of these heavy metals. Heavy metals can occur in an organic or inorganic form (organic here refers to the chemical definition of containing carbon, not to organic growing methods) and for some heavy metals, such as mercury and arsenic, the form determines the toxicity. Inorganic arsenic is harmful to health and is a known carcinogen, while organic arsenic is much less harmful.⁵ In the case of mercury, organic mercury (most commonly found in food as methylmercury) is considered the most toxic form because it can reach the placenta and cross the blood brain barrier, while inorganic mercury cannot (although both can cause other harms).⁶ This is problematic when a report gives only “total” heavy metal levels without differentiating the amounts of organic and inorganic, because we don’t need to worry as much about some forms.

What can I do?

We can ensure that our bodies’ detoxification capabilities are supported every day by eating a nutrient dense diet built on vegetables, healthy fats, and proteins. Adequate sleep, plenty of clean water, and regular exercise also support detoxification. Beyond that, we can limit our exposure to heavy metals in meaningful ways by employing the following practices:

• Drink purified water. Water is one of our greatest sources of heavy metal exposure.
• Choose organic food. While organic food can also contain heavy metals, organic production methods avoid the use of synthetic fertilizers and pesticides, which contribute to the heavy metal burden of our soils and environment.⁷ Choosing organic also limits our exposure to pesticides; the combined burden of heavy metals and pesticides has not yet been fully explored but their combination is expected to have a potentiating effect.⁸ 
• If you smoke or vape, quit. Cigarettes and e-cigarettes are major sources of heavy metal exposure for smokers and those exposed to second-hand smoke.^{9 10 11}
• Aim to eat a variety of foods regularly. This not only increases the likelihood of consuming all beneficial nutrients, but also reduces the risk of eating too much of a food that is higher in heavy metals.
• Take a multivitamin. A deficiency of essential vitamins and minerals may increase one’s susceptibility to heavy metal toxicity.¹² Conversely, there is some evidence that replenishing essential vitamins and minerals can help counter the negative effects of heavy metals.
• Take a probiotic supplement and/or consume probiotic-rich fermented foods. In vitro, many strains of beneficial bacteria are able to bind and sequester heavy metals, and in animal and preliminary human studies probiotics have decreased the heavy metal burden.^{13 14 15 16 17 18}
• Take chlorella regularly. This nutrient-dense alga binds heavy metals and increases their excretion.¹⁹ In animal studies, chlorella administered concurrently with heavy metals has protected liver function and protected against oxidative stress.^{20 21}
• Choose fish and seafood wisely. Use Monterey Bay Aquarium Seafood Watch Consumer Guides or the Environmental Working Group’s Consumer Guide to Seafood to choose fish and seafood that is lowest in mercury.   
• Take extra precautions if you are pregnant or nursing or if you are feeding young children.

References

1. World Health Organization (n.d.). 10 chemicals of public health concern. World Health Organization. https://www.who.int/news-room/photo-story/photo-story-detail/10-chemicals-of-public-health-concern
2. Tchounwou, P.B., Yedjou, C.G., Patlolla, A.K., Sutton, D.J. (2012). Heavy metals toxicity and the environment. Experientia supplementum, 101, 133–164. https://doi.org/10.1007/978-3-7643-8340-4_6
3. Balali-Mood, M., Naseri, K., Tahergorabi, Z., Khazdair, M.R., Sadeghi, M. (2021). Toxic mechanisms of five heavy metals: mercury, lead, chromium, cadmium, and arsenic. Front Pharmacol, 12. https://doi.org/10.3389/fphar.2021.643972
4. Department of Public Health. (n.d.). Lead in Candy Faqs. Lead in Candy FAQs. https://www.cdph.ca.gov/Programs/CEH/DFDCS/Pages/FDBPrograms/FoodSafetyProgram/LeadinCandyFAQs.aspx  
5. World Health Organization. (2022, December 7). Arsenic. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/arsenic
6. Patrick, L. (2002). Mercury toxicity and antioxidants: part I: glutathione and alpha-lipoic acid in the treatment of mercury. Alt Med Rev, 7(6).  https://altmedrev.com/wp-content/uploads/2019/02/v7-6-456.pdf
7. Defarge, N., de Vendômois, J.S., Séralini, G.E. (2018). Toxicity of formulants and heavy metal in glyphosate-based herbicides and other pesticides. Toxicology Reports, 5, 156-163. https://doi.org/10.1016/j.toxrep.2017.12.025
8. Wallace, D.R., Djordjevic, A.B. (2020). Heavy metal and pesticide exposure: a mixture of potential toxicity and carcinogenicity. Current Opinion in Toxicology, 19, 72-79. https://doi.org/10.1016/j.cotox.2020.01.001
9. Caruso, R.V., C’Connor, R.J., Stephens, W.E., Cummings, K.M., Fong, G.T. (2014). Toxic metal concentrations in cigarettes obtained from U.S. smokers in 2009: results from the international tobacco control (ITC), United States survey cohort. Int J Environ Res Public Health, 11(1), 202-217.  doi: 10.3390/ijerph110100202
10. Zhao, D., Aravindakshan, A., Hilpert, M., Olmedo, P., Rule, A.M., Navas-Acien, A., Aherrera, A. (2020). Metal/metalloid levels in electronic cigarette liquids, aerosols, and human biosamples: a systematic review. Environ Health Perspect, 128(3), 036001. doi: 10.1289/EHP5686
11. Auman-Gooding, K. (2023, June 27). Tobacco smoke exposure may increase heavy metals in children’s saliva. PennState Social Science Research Institute. Retrieved from https://www.psu.edu/news/social-science-research-institute/story/tobacco-smoke-exposure-may-increase-heavy-metal-levels/  
12. Zhai, Q., Narbad, A., Chen, W. (2015). Dietary strategies for the treatment of cadmium and lead toxicity. Nutrients, 7(1), 552-571.  doi: 10.3390/nu7010552
13. Probiotic potential for heavy metal detoxification. The Institute for Functional Medicine. (2022, October 22). https://www.ifm.org/news-insights/probiotic-potential-for-heavy-metal-detoxification/
14. Daisley, B., A., Monachese, M., Trinder, M., Bisanz, J.E., Chmeil, J.A., Burton, J.P., Reid, G. (2019). Immobilization of cadmium and lead by Lactobacillus rhamnosus GR-1 mitigates apical-to-basolaterol heavy metal translocation in a Caco-2 model of the intestinal epithelium. Gut Microbes, 10(3). https://doi.org/10.1080/19490976.2018.1526581
15. Nakamura, I., Hosokawa, K., Tamura, H., & Miura, T. (1977). Reduced mercury excretion with feces in germfree mice after oral administration of methyl mercury chloride. Bulletin of environmental contamination and toxicology, 17(5), 528–533. https://doi.org/10.1007/BF01685974
16. Muhammad, Z., Ramzan, R., Zhang, R., Zhao, D., Gul, M., Dong, L., Zhang, M. (2021). Assessment of in vitro and in vivo bioremediation potentials of orally supplemented free and microencapsulated Lactobacillus acidophilus KLDS strains to mitigate the chronic lead toxicity. Front Bioeng Biotechnol, 9.  https://doi.org/10.3389/fbioe.2021.698349
17. Feng, P., Yang., J., Zhao, S., Ling, Z., Han, R., Wu, Y., Salama, E.S., Kakade, A., Khan, A., Jin, W., Zhang, W., Jeon, B.H., Fan, J., Liu, M., Mamtimin, T., Liu, P., Li, X. (2022). Human supplementation with Pediococcus acidilactici GR-1 decreases heavy metals levels through modifying the gut microbiota and metabolome. npj Biofilms Microbiomes, 8(63). https://doi.org/10.1038/s41522-022-00326-8
18. Bisanz, J. E., Enos, M. K., Mwanga, J. R., Changalucha, J., Burton, J. P., Gloor, G. B., & Reid, G. (2014). Randomized open-label pilot study of the influence of probiotics and the gut microbiome on toxic metal levels in Tanzanian pregnant women and school children. mBio, 5(5), e01580-14. https://doi.org/10.1128/mBio.01580-14
19. Yadav, M., Kumar, V., Sandal, N., Chauhan, M.K. (2022). Quantitative evaluation of Chlorella vulgaris for removal of toxic metals from body. J Applied Phycology, 34, 2743-2754. https://doi.org/10.1007/s10811-021-02640-8
20. Shim, J. Y., Shin, H. S., Han, J. G., Park, H. S., Lim, B. L., Chung, K. W., & Om, A. S. (2008). Protective effects of Chlorella vulgaris on liver toxicity in cadmium-administered rats. Journal of medicinal food, 11(3), 479–485. https://doi.org/10.1089/jmf.2007.0075
21. Farag, M. R., Alagawany, M., Mahdy, E. A. A., El-Hady, E., Abou-Zeid, S. M., Mawed, S. A., Azzam, M. M., Crescenzo, G., & Abo-Elmaaty, A. M. A. (2023). Benefits of Chlorella vulgaris against Cadmium Chloride-Induced Hepatic and Renal Toxicities via Restoring the Cellular Redox Homeostasis and Modulating Nrf2 and NF-KB Pathways in Male Rats. Biomedicines, 11(9), 2414. https://doi.org/10.3390/biomedicines11092414