Alarming heavy metal levels found in US cocoa products

By Pooja Toshniwal PahariaReviewed by Benedette Cuffari, M.Sc.Aug 4 2024

In a recent study published in the journal Frontiers in Nutrition, researchers evaluated heavy metal levels in cocoa-based consumer products in the United States over an eight-year period.

Study: A multi-year heavy metal analysis of 72 dark chocolate and cocoa products in the USA. Image Credit: DesignMarjolein / Shutterstock.com

Heavy metal contamination in cocoa

Cocoa food products are high in dietary polyphenols associated with numerous health benefits. The close proximity of cocoa fields to other pollution sources may lead to heavy metal contamination in dark chocolate products. In fact, several studies have reported the presence of heavy metals such as lead, cadmium, and arsenic in these products; however, the extent of this contamination remains unclear.

Exposure to cadmium has been associated with various adverse health effects, some of which include cardiovascular disease, renal failure, cognitive impairment, diabetes, cancer, and osteoporosis. Thus, improving food quality, particularly for young children and pregnant women, is strongly advised.

About the study

The researchers examined 72 cocoa products for the presence of cadmium, arsenic, and lead between 2014 and 2022. Threshold values were used to evaluate heavy metal exposure based on the Prop 65 maximum acceptable dosage levels (MADLs) of 0.50 micrograms (µg) for lead, 4.10 µg for cadmium, and 10 µg for arsenic daily.
Cocoa products were purchased from third-party internet shops, manufacturer or supplier websites, and physical stores. All items were local or European in origin and purchased domestically.

The lead content analysis involved digesting samples with trace metal-grade concentrated hydrochloric acid, hydrogen peroxide, and nitric acid before diluting them to 50 mL with deionized water. Cadmium and arsenic examination involved digesting samples with nitric acid of trace metal-grade concentration and then diluting them with 200 mL of deionized water. Inductively coupled plasma-mass spectroscopy (ICP-MS) was used to determine heavy metal concentration.

Calibrations were established at 0.001, 0.05, 0.10, and 0.5 parts per million (ppm). Two independent laboratories retested samples exceeding these measurements.

Random- and fixed-effect multivariable linear regressions were used to assess the effects of specific and third-party certifications on lead, arsenic, and cadmium concentrations while controlling for the calendar year. Marginal linear projections allowed the researchers to estimate the year's influence on heavy metal contamination.

Bonferroni adjustments were utilized for marginal comparisons. Moreover, multivariable ordinary-type least squares modeling was used to determine the robustness of the findings and assess the impact of cohort years on heavy metal contamination. Welch's T-test was used to assess the role of organic compounds in a metal context.

Study findings

About 43%, 35%, and 0% of cocoa products exceeded the permitted limits for lead, cadmium, and arsenic concentrations, respectively, whereas 97% were below lead cutoff values imposed by the United States Food and Drug Administration (FDA).

Among all samples, the mean amounts of lead and cadmium exceeded Prop 65 MADL levels at 0.6 and 4.4 µg/serving, respectively. However, the median quantities of lead and cadmium were lower at 0.4 and 3.0 µg/day, respectively, than the cautious Prop 65 MADLs, thus indicating that cocoa product outliers may have had a significant impact on these results.

These results indicate that heavy metal contamination in more than half of the tested products may not pose significant risks to the average individual when consuming a single serving. However, consuming two or more servings every day, combined with the consumption of non-cocoa-derived heavy metal sources, may increase heavy metal exposure to levels above MADL values.

Organic cocoa products had significantly higher cadmium levels at 3.2 µg/serving than dark chocolate or cocoa. Organic products were also more likely to have higher concentrations of cadmium and lead.

The FDA has not created interim reference levels (IRLs) for cadmium or arsenic; however, lead levels are much lower than U.S. legal limits for pregnant women and children under seven years of age. Trade certifications and organic designations do not decrease lead, cadmium, or arsenic levels. Samples obtained in 2016, 2019, and 2022 exhibited lower heavy metal concentrations than 2014 samples, with considerably lower lead concentrations observed between 2022 and 2019.

Conclusions

Many of the cocoa products tested in the current study were contaminated with cadmium and lead levels that may exceed Prop 65 legal restrictions. Thus, there remains an urgent need for improved food monitoring and additional research into cumulative heavy metal exposure from diets.