The researchers conducted an extensive examination of 48 different chocolate products across multiple categories, including cocoa powder, chocolate chips, milk chocolate bars, and mixes for brownies, chocolate cake, and hot chocolate. The study found that 16 out of the 48 products surpassed the agreed limits for lead and cadmium content in food products.

The study included products from multinational manufacturers such as Hersheys, Ghirardelli, and Nestlé; national retailers like Costco, Target, Trader Joes, Walmart, and Whole Foods; and smaller producers such as Droste and Navitas.

Risk of exposure to heavy metals was assessed by measuring the content of four heavy metals (lead, cadmium, arsenic, and mercury) contained in one product serving against the standard maximum allowable dose levels (MADLs) currently in place in the state of California. Although none of the products posed a risk of arsenic or mercury exposure, one-third surpassed agreed levels for lead (0.5 micrograms per day) and cadmium (4.1 mcg per day).

Risk of exposure greatest from dark chocolate

These findings follow an initial report published by Consumer Reports last December which found cadmium and lead to be present in 100% of the 28 dark chocolate bars tested.

Over 80% of the bars included in the study were found to contain amounts of heavy metals above Consumer Reports’ safe levels. Five products contained exceedingly high levels of both lead and cadmium, including Trader Joes The Dark Chocolate Lovers Chocolate 85% Cacao, Green & Blacks Organic Dark Chocolate 70% Cacao, and Theo Organic’s Extra Dark Pure Dark Chocolate 85% Cocoa.

The latest research also shows that dark chocolate bars tended to have higher levels of heavy metals, with 71% exceeding Consumer Reports’ basis for lead and cadmium. based on a recommended serving size of approximately one ounce, Perugina’s 85% Premium Dark Chocolate was reported to contain volumes of lead and cadmium exceeding the threshold by 539% and 68%, respectively.

On the other hand, milk chocolate, which generally contains lower levels of cocoa, fared better, with no products tested exceeding the set limits.

Pregnant women and children most at risk

Cocoa, the key ingredient giving chocolate its distinct flavour, was identified as the most likely source of heavy metals in the chocolate products assessed in the study. These toxic elements are not introduced during chocolate manufacturing but during the cultivation and processing of cocoa.

Research from the organisation suggests that cadmium is absorbed into the cocoa plant via the soil, while lead is deposited onto the cocoa beans from dust and soil during the post-harvest process.

Overexposure to heavy metals can cause damage to the brain and nervous system, leading to delays in development and learning and behavioural problems in children. In adult populations, regular exposure to lead is related to problems with the immune and reproductive systems, as well as kidney damage and hypertension, studies show.