In light of recently raised concerns about the levels of toxic heavy metals in chocolate, researchers from Tulane University assessed the levels and risks of toxic metals in chocolates sold in the U.S., made from cocoa originating from different global regions. The findings revealed that, in nearly all chocolate samples, toxic heavy metals were below the recommended safe levels, although the levels of certain metals varied depending upon the origins of the cocoa beans used to make the chocolates.

The presence of contaminants in cacao-derived products such as chocolates has raised global health concerns. For example, in 2022 and in 2023, Consumer Reports produced the findings of two research projects suggesting a concerning presence of cadmium and lead among chocolates and cocoa-containing products. Tulane researchers’ findings indicate, however, that an ounce of dark chocolate daily poses no health concern for adults, with only minor concern for children’s exposure to cadmium.

To explore the extent to which toxic heavy metals in chocolates pose a health risk to U.S. consumers, the Tulane researchers collected 155 chocolate samples and assessed them for 16 elements (arsenic, cadmium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, selenium, strontium, thallium, thorium, uranium, and zinc). Purchased from brick-and-mortar national supermarkets and online retailers, the pool of samples mostly represented brands Alter Eco, Beyond Good, Blanxart, Chuao, Dick and Taylor, Dove, Endangered Species, Ghirardelli, Hershey, Ki'Xocolatl, Lindt, Lily's, Marou, Napolitains, Pralus Pyramid, Taza, and Theo. The provenance of cacao for the chocolate samples was categorized into five major regions: West Africa (33 samples), South America (27 samples), Asia Pacific (ten samples), Central America (ten samples), and East Africa (nine samples), as well as mixed-origin cacao sourced from various regions (61 samples). The origins of four samples were unknown.

The potential non-carcinogenic risk of long-term exposure to contaminants (cadmium, lead, nickel, arsenic, and uranium) was determined using hazard quotient (HQ) or hazard index (HI), proposed by the U.S. Environmental Protection Agency (EPA). Intakes of toxic metals cadmium, lead, nickel, arsenic, and uranium were estimated assuming daily chocolate consumption of one ounce.

Analysis of the samples showed that dark chocolates (50 percent or more cocoa content) sourced from Central and South America exhibited the highest mean levels of cadmium, and South American samples also contained elevated lead. On the other hand, samples from West Africa and Asia had low cadmium and lead, respectively. Higher cacao contents showed strong association with cadmium and nickel levels, and moderate association with arsenic. Weak association of cocoa contents with lead and uranium indicates post-harvest contamination, rather than contamination of the cocoa bean during cultivation.

Cadmium levels in chocolate samples ranged from 0.3–843 micrograms per kilogram (µg/kg), with the highest level of 843 µg/kg found in Lok Dark Chocolate (with 100 percent cocoa) from Columbia, followed by Marou from Vietnam (722 µg/kg), Mexican Vivio Foods organic cacao powder (689 µg/kg), and Peruvian Pascha dark chocolate chips (536 µg/kg). Only the chocolate sample from Colombia exceeded the maximum level for cadmium set by the European Commission (800 µg/kg). However, two samples exceeded the state of California's interim level for cadmium in samples with 65–95 percent cacao content (450 µg/kg).

Regarding lead, levels in samples ranged from 1.9–632 µg/kg, with the highest level of 632 µg/kg found in in Napolitains Dark from Venezuela, followed by Blanxart chocolate from Peru (525 μg/kg). These two dark chocolate samples also exceeded California’s interim level of 150 µg/kg for chocolates with 65–95 percent cacao content.

For the most part, the levels of toxic heavy metals in the chocolate samples did not exceed EPA HQ/HI values. Still, some samples surpassed safe levels of cadmium and/or combined levels of toxic heavy metals for children weighing 15 kilograms kg (33 pounds) or less. Specifically, the HQ for cadmium was exceeded in four samples, and the HI for cumulative risk of cadmium, lead, nickel, arsenic, and uranium was exceeded in 33 dark chocolates, indicating potential non-carcinogenic risks for children, but not for adults.

Interestingly, the researchers also found the sampled dark chocolates to contain significant levels of copper, iron, magnesium, manganese, and zinc, which can also restrict bioavailability of cadmium and lead.