Concentrations of heavy metals found in single servings of some chocolates and cocoa-based products are too low in most cases to pose a health risk to consumers, according to research set to be published in the journal Frontiers.

Some consumer groups and independent test agencies have previously reported heavy metal contamination in cocoa products such as dark chocolate, with possible causes being the type of soil where cocoa is grown and industrial processing. Researchers at the George Washington University School of Medicine and ConsumerLab.com analyzed 72 cocoa-containing products and found that 70 of them fell below limits set by the FDA for lead contamination.

The findings of their study showed that the products may not pose a health risk when consumed as single servings, though larger portions could exceed strict California limits set in a law known as Prop 65. The recommended single serving for chocolate is about 1 oz to 2 oz (30 gm to 60 gm).

"If contaminated products as a whole are consumed in small amounts and infrequently by most, these contaminants may not be a public health concern," the paper stated. "In contrast, if many such products are consumed fairly regularly by the average consumer, the additive exposure may be a public health concern."

The long-running research analyzed 72 products for potential contamination with heavy metals such as lead, cadmium, and arsenic in four different cohorts in 2014, 2016, 2019, and 2022. The researchers noted that the "median concentrations of each metal tested were lower than even the conservative Prop 65."

However, they added that "consuming some of the products tested, or more than one serving per day in combination with non-cocoa derived sources ... may add up to exposure that would exceed the Prop 65 (limits)."

The researchers used the California legislation as a benchmark for the study because it sets limits on contamination for the three types of heavy metals tested, while the FDA regulation only sets limits for lead. The paper concluded with a call for more testing of consumer products.