Led by George Washington University (GW), an analysis of U.S. dark chocolate and cocoa products revealed one-third of samples to contain cadmium levels exceeding maximum allowable limits, and close to half of products contained lead levels exceeding maximum allowable limits. Interestingly, organic-labeled products were found to have higher levels of lead and cadmium than non-organic samples, and concentrations of toxic heavy metals in all sample types were seen to reduce over time.

Cadmium and lead are naturally occurring, toxic metals in the environment. Cocoa plants take up cadmium from soils through their roots and deposit the element into the nibs of cocoa beans. Lead can be introduced to cocoa from various sources including soil, dust, and deposition from power plants.

Concern about these toxic heavy metals in chocolates and chocolate products is not new; for example, watchdog group Consumer Reports has published results of its own analyses showing elevated lead and cadmium levels in chocolates and cocoa, most recently in October 2023.

The multi-year, GW-led project aimed to provide information about the significance of toxic heavy metals contamination in cocoa-containing products sold in the U.S., and to derive trends over time regarding the degree and scope of contamination.

Lead and Cadmium Exceed (Some) Maximum Levels Considered “Safe”

Between 2014 and 2022, the researchers collected 72 cocoa-containing products at retail. The products were tested for lead, cadmium, and arsenic in four cohorts (2014, 2016, 2019, and 2022). The maximum allowable limits for the toxic heavy metals used as reference points in the study were based on the maximum allowable dose levels (MADLs) described in California’s Proposition 65 (formally known as the Safe Drinking Water and Toxic Enforcement Act of 1986), specifically: 0.5 micrograms per day (μg/day) for lead, 4.1 μg/day for cadmium, and 10 μg/day for arsenic.

The results found 43 percent of samples exceeded Proposition 65 MADLs for lead, and 35 percent of samples exceeded the MADLs for cadmium. None of the samples surpassed the Proposition 65 MADLs for arsenic. Median concentrations of each metal tested were lower than the Proposition 65 MADLs.

However, when the U.S. Food and Drug Administration’s (FDA’s) interim reference level (IRL) for lead was used as the benchmark, 97.2 percent of samples (70 of 72 samples) did not exceed the IRL. FDA’s lead IRL is more liberal than the Proposition 65 lead MADL.

Specifically, mean concentrations of lead resulted in levels nearly four times lower than FDA’s most conservative lead IRL for children younger than seven years of age (2.2 μg/day). When FDA’s limits for females of childbearing age were used, mean concentrations of lead resulted in levels 12 times lower than the 8.8 µg/day IRL.

The GW researchers note that any intake of lead, especially among vulnerable populations, should be “heavily scrutinized,” because there has never been a safe blood serum level of lead consumption; even those who test below the U.S. Centers for Disease Control and Prevention’s (CDC’s) blood lead reference value of 3.5 μg/deciliter of blood (from which FDA derived its IRLs using dietary conversion factors) are at risk for a range of adverse effects.

FDA IRLs have not been established for cadmium or arsenic.

In general, the GW researchers conclude that heavy metal contamination, in the majority of products surveyed, may not pose a risk for the average person when consumed as a single serving; however, consuming more than one serving per day and/or in combination with other sources of heavy metals (e.g., seafood) may cumulatively add up to exposure that exceed the conservative Proposition 65 MADLs.

Other Findings and Trends

Surprisingly, when the researchers compared products labeled as “organic” to their non-organic counterparts, organic samples were significantly more likely to display higher levels of cadmium (0.4 μg /g) and lead (0.02 μg /g).

Moreover, as a whole, products in later cohorts (2016, 2019, and 2022) demonstrated lower concentrations of all heavy metals when compared with those in the 2014 cohort. Significantly lower concentrations of lead were documented between the years 2022 and 2014, as well as the years 2019 and 2014.

Industry Response and Contamination Mitigation Strategies

Following the release of the GW project’s findings, the National Confectioner’s Association (NCA) stated, “Chocolate and cocoa are safe to eat and can be enjoyed as treats as they have been for centuries. Food safety and product quality remain our highest priorities and we remain dedicated to being transparent and socially responsible.” In August 2022, NCA released the results of a three-year study that explored ways to reduce the presence of cadmium and lead in cocoa and chocolate, including a list of recommended strategies for industry to mitigate the toxic elements present in cocoa-based products. A summary can be read here.

Finally, in June 2024, a Tulane University study revealed which chocolates sold in the U.S., made from cocoa originating from different global regions, had the highest and lowest levels of toxic heavy metals. The findings showed that samples from West Africa and Asia had low cadmium and lead. A summary can be read here.