Heavy Metals in Natural Ingredients: Clays, Seaweed, Cocoa, Shilajit
What published testing found about lead, cadmium and arsenic in cocoa, seaweed, clays and shilajit, why results vary, and who should be most careful. No brands.
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Quick answer: published testing has found lead, cadmium, arsenic or other metals in some samples of cocoa, seaweed, clay and shilajit. Amounts vary widely between samples and sources, many studies are small, and a detected metal does not by itself show that a product harmed anyone. The FDA says there is no known safe level of exposure to lead, so the question is worth asking, especially for children and pregnancy.
Urgent: if a child or anyone else has swallowed clay or another product not made to be eaten, or feels very unwell after a product, call Poison Help at 1-800-222-1222 (US). Call 911 for collapse, seizure, trouble breathing, or swelling of the face or throat.
Why metals turn up in natural ingredients
Lead may be present in food from the environment where foods are grown, raised or processed. [1] For cocoa, FDA scientists describe cadmium and lead coming from natural and human-made sources, with higher cadmium in some cocoa from parts of Latin America. [2] The FDA states that lead is toxic to humans and can affect people of any age or health status, and that the very young are particularly vulnerable. [1] For adults, chronic lead exposure is associated with kidney dysfunction, high blood pressure and effects on thinking. [1]
The FDA also says that testing results that detect lead do not necessarily mean a food should be avoided, and that eating a variety of nutrient-dense foods can limit exposure to a contaminant from one food. [1]
What published testing found
Evidence labels: these are laboratory measurements and exposure estimates, not studies of health outcomes in people who used the products.
| Ingredient | What the studies found | Limits |
|---|---|---|
| Cocoa and chocolate (Theobroma cacao L., seeds) [3] | In 72 US dark chocolate and cocoa products tested between 2014 and 2022, 43% were above the California Prop 65 level used by the authors for lead and 35% for cadmium; none were for arsenic. Median levels of each metal were below those levels. "Organic" products were significantly more likely to have higher cadmium and lead. [4] Two studies by consulting-firm authors: a lead model found typical chocolate intake is a small share of overall lead exposure, [5] and an analysis of 36 chocolate bars concluded health risks from heavy metals are unlikely under typical exposure, although high-end exposure assumptions gave potential lead risks for most age groups. [6] | Reference levels differ by study. Some authors worked for a product-testing company or a consulting firm, as the papers disclose. See Cacao and cocoa and Dark chocolate and cocoa as food. |
| Seaweed (including hijiki, Sargassum fusiforme) [7] | A UK government laboratory found total arsenic in all 31 retail dried seaweed samples. Inorganic arsenic, which can cause liver cancer, was found only in the nine hijiki samples, and the UK Food Standards Agency advised consumers to avoid eating it. [8] A 2024 survey of 25 seaweeds found the highest total arsenic in brown seaweeds, mostly as arsenosugars, and low risk from inorganic arsenic except for hijiki, which it calls Hizikia fusiforme. [9] LactMed says kelp (bladderwrack) can also contain arsenic, cadmium and lead. [10] | The UK advice dates from the 2007 study; we did not read a current agency statement. Iodine is a separate seaweed concern: see Seaweed, iodine and the thyroid. |
| Spirulina (Arthrospira platensis, also written Spirulina platensis) [11][12] | LactMed says products grown in uncontrolled conditions can contain heavy metals, and some can carry microcystins, liver toxins from a contaminating alga. [13] | A reference summary, not product testing. See Spirulina and chlorella. |
| Clays (traditional and "health" clays) | A Dutch food-safety authority tested 27 health clays and 36 traditional clays for oral use. Maximum levels were 99.7 mg/kg lead, 45.1 arsenic, 2.2 mercury and 0.75 cadmium. [14] With no legal maximum for such clays, the authors estimated that, for lead, two of the 27 health clays would give intakes above the toxicological limit by up to 20-fold, and they advised that use of these products, especially by pregnant women, should be discouraged. [14] | Samples were collected 2004 to 2012. Intake was estimated, not measured. |
| Clays on skin (animal study) | In mice, a green clay paste with high arsenic and lead, applied to shaved skin daily for two weeks, raised lead levels in liver and kidney compared with controls. [15] | Preclinical (animals). It does not show what happens in people. See Bentonite clay and Kaolin clay. |
| Shilajit (a complex natural exudate, not a plant) | A review says it contains around 65 heavy metals including toxic ones, and that reported levels were below WHO and FDA limits except in a few studies. [16] A laboratory study of two types sold globally found several metals above permissible limits, [17] while a 2026 study of 12 samples found toxic metals below established thresholds. [18] Thallium was higher in some supplements than in crude shilajit. [19] | Mixed. Results differ by sample, origin and method. See Shilajit contamination and heavy metals. |
Who should be most careful
Children, pregnancy and kidney disease come up in the sources: the very young are particularly vulnerable to lead, [1] the Dutch authors advised against use of the clays by pregnant women, [14] and chronic lead exposure in adults is linked to kidney dysfunction. [1] If this applies to you, ask a clinician or pharmacist before using clay, shilajit, kelp or similar products. See Pregnancy and breastfeeding and Kidney, liver or thyroid cautions.
What a reader can do
- Do not swallow clay or other products that are not sold as food or supplements. See Natural substances not meant to be swallowed.
- Ask whether a company publishes batch test results, and what the tests covered. See Third-party testing and certifications and Heavy metals in supplements and herbal products. A test report does not certify safety or effectiveness. [10]
- Keep the variety in your diet; the FDA says this helps limit exposure from any one food. [1]
- Report a problem through MedWatch. [21]
Frequently asked questions
Is dark chocolate dangerous because of lead and cadmium?
The studies we read measured metals in chocolate and then estimated exposure. They found some products above the authors' reference levels, [4] while modeling studies concluded risk is unlikely under typical intake for most chocolate bars. [6] The studies we read did not report illness outcomes. Ask a clinician if you or a child are in a higher-risk group.
Is hijiki seaweed safe?
In a 2007 UK study, inorganic arsenic was found only in hijiki, and the UK Food Standards Agency advised consumers to avoid eating it. [8] A 2024 survey also singled out hijiki among the seaweeds it studied. [9]
Does organic mean fewer heavy metals?
Not in the one study we read. Organic cocoa products were significantly more likely to have higher cadmium and lead. [4] It is a single sample, so it does not show that organic products are worse overall.
Are clays a safe "detox"?
We found no evidence of benefit in the sources read for this page, and the Dutch testing found some clays could give intakes above the toxicological limit for lead. [14] See Detox claims.
Can a lab report prove a product is safe?
No. A manufacturer can hire an independent organization to verify quality, but LactMed says that does not certify safety or effectiveness. [10]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read these results
- Detected is not the same as harmful. The FDA says detection does not necessarily mean a food should be avoided. [1] It also says the potential for harm varies with the level of lead, the age of the consumer, and the length, amount and frequency of exposure. [1]
- Different studies use different yardsticks (California Prop 65 levels, WHO and FDA herbal limits, toxicological limits), so figures from one table cannot be compared with another.
- One sample is not a whole market. None of these studies tests every product, and we do not name or rank products.
- A natural source does not protect. The FDA says an ingredient's source does not determine its safety. [20]
References
- U.S. Food and Drug Administration. Lead in Food, Foodwares, and Dietary Supplements. Read 2026-10-23.
- Abt E, Robin LP. Perspective on Cadmium and Lead in Cocoa and Chocolate. J Agric Food Chem. 2020;68(46):13008-13015. PubMed 32293881. Authors are at the FDA Center for Food Safety and Applied Nutrition. Read 2026-10-23.
- GBIF Secretariat. GBIF Backbone Taxonomy, species match for Theobroma cacao. Checked 2026-10-23. Read 2026-10-23.
- Hands JM, et al. A multi-year heavy metal analysis of 72 dark chocolate and cocoa products in the USA. Front Nutr. 2024;11:1366231. PubMed 39144282. Some authors were employed by a product-testing company, as the paper discloses. Read 2026-10-23.
- Thornton SA, et al. Probabilistic biokinetic lead modeling to quantify relative contribution of chocolate bar intake to blood lead levels. Food Chem Toxicol. 2026;210:115979. PubMed 41592635. Authors were employed by a consulting firm, as the paper discloses. Read 2026-10-23.
- Thornton SA, et al. Analytical measurement and human health risk assessment of selected metals from commercial chocolate bars. Food Chem Toxicol. 2026;211:116011. PubMed 41692062. Authors were employed by a consulting firm, as the paper discloses. Read 2026-10-23.
- GBIF Secretariat. GBIF Backbone Taxonomy, species match for Sargassum fusiforme. Checked 2026-10-23. Read 2026-10-23.
- Rose M, et al. Arsenic in seaweed: forms, concentration and dietary exposure. Food Chem Toxicol. 2007;45(7):1263-1267. PubMed 17336439. UK Defra laboratory study of retail dried seaweed. Read 2026-10-23.
- Yu Y, et al. Survey of arsenic content in edible seaweeds and their health risk assessment. Food Chem Toxicol. 2024;187:114603. PubMed 38499235. Read 2026-10-23.
- Drugs and Lactation Database (LactMed). Seaweed. National Institute of Child Health and Human Development; record dated 2024-10-15. PubMed 30000910. Read 2026-10-23.
- GBIF Secretariat. GBIF Backbone Taxonomy, species match for Arthrospira platensis. Checked 2026-10-23. Read 2026-10-23.
- GBIF Secretariat. GBIF Backbone Taxonomy, species match for Spirulina platensis. Checked 2026-10-23. Read 2026-10-23.
- Drugs and Lactation Database (LactMed). Spirulina. National Institute of Child Health and Human Development; record dated 2021-06-21. PubMed 30000909. Read 2026-10-23.
- Reeuwijk NM, et al. Levels of lead, arsenic, mercury and cadmium in clays for oral use on the Dutch market and estimation of associated risks. Food Addit Contam Part A. 2013;30(9):1535-1545. PubMed 23862762. Read 2026-10-23.
- Whiteside TE, et al. Elevated Arsenic and Lead Concentrations in Natural Healing Clay Applied Topically as a Treatment for Ulcerative Dermatitis in Mice. J Am Assoc Lab Anim Sci. 2020;59(2):212-220. PubMed 32059757. Animal study. Read 2026-10-23.
- Hussain A, Saeed A. Hazardous or Advantageous: Uncovering the Roles of Heavy Metals and Humic Substances in Shilajit. Biol Trace Elem Res. 2024;202(12):5794-5814. PubMed 38393486. Review. Read 2026-10-23.
- Aldakheel RK, et al. Rapid Determination and Quantification of Nutritional and Poisonous Metals in Vastly Consumed Ayurvedic Herbal Medicine (Rejuvenator Shilajit). Biol Trace Elem Res. 2022;200(9):4199-4216. PubMed 34800280. Read 2026-10-23.
- Kamgar E, et al. Characterization of metal composition and molecular weight distribution in Shilajit. J Trace Elem Med Biol. 2026;96:127913. PubMed 42364294. Read 2026-10-23.
- Kamgar E, et al. Quantifying of thallium in Shilajit and its supplements. BMC Chem. 2025;19:20. PubMed 39827344. Read 2026-10-23.
- U.S. Food and Drug Administration. "Organic" Cosmetics. Content current as of February 25, 2022. Read 2026-10-23.
- U.S. Food and Drug Administration. MedWatch: The FDA Safety Information and Adverse Event Reporting Program. Content current as of October 21, 2026. Read 2026-10-23.