Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. 
Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. What was studied?
This original research article investigates the sources and extent of lead contamination in cocoa beans, cocoa bean shells, soils from Nigerian cocoa farms, and manufactured cocoa and chocolate products. The study was motivated by persistent findings of high lead concentrations in chocolate products worldwide, despite cocoa beans themselves being considered naturally low in lead. The researchers specifically aimed to determine baseline lead concentrations and isotopic signatures in Nigerian cocoa beans and soils, as well as to trace possible sources and stages of lead contamination by analyzing the isotopic composition of lead in cocoa bean shells, processed cocoa, and chocolate products. By comparing these isotopic profiles to those of known industrial lead aerosols and regional gasoline additives, the study sought to clarify whether contamination primarily arises at the agricultural stage, during processing, or through environmental exposure during manufacturing and distribution.
Who was studied?
The study focused on cocoa beans, cocoa bean shells, and soils from six farms in Nigeria’s three highest cocoa-producing states: Ondo, Osun, and Ogun. Composite samples were collected at various soil depths and at different stages of bean processing, including freshly harvested and fermented/dried beans. In addition, the research included a range of finished chocolate products and processed cocoa powders sourced from international markets, as well as cocoa beans from other countries for comparative purposes. The analytical protocols adhered to strict trace metal contamination controls, ensuring the reliability of the findings. This approach allowed the researchers to examine both the local context of Nigerian cocoa production (which supplies a significant portion of the world’s cocoa) and the broader issue of industrial lead contamination in globally distributed chocolate products.
Most important findings
| Critical Points | Details |
|---|---|
| Baseline lead in cocoa beans | Nigerian cocoa beans had extremely low lead concentrations, averaging <0.5 ng/g, among the lowest reported for any natural food. |
| Lead in cocoa shells | Cocoa bean shells contained much higher lead concentrations (average: 160 ng/g), likely due to their high capacity to adsorb atmospheric lead during fermentation and drying at farms. |
| Lead in manufactured products | Processed cocoa and chocolate products exhibited significantly higher lead concentrations (up to 230 ng/g in cocoa and 70 ng/g in chocolates), about 60 times higher than the beans themselves, and among the highest for any foods. |
| Isotopic evidence of contamination | Isotopic signatures indicated that bean shell contamination aligns with atmospheric lead from gasoline emissions, likely from the ongoing use of leaded gasoline in Nigeria. Manufactured products, however, displayed broader isotopic variability, implicating additional industrial sources during shipping and processing. |
| Regulatory exceedance | Some chocolate products, especially those in India, exceeded international maximum permissible lead levels, posing a potential risk to children who are particularly susceptible to lead exposure. |
| Limited contamination at farm level | The low lead content of beans and the isotopic evidence suggest that most contamination occurs after beans leave the farm, during shipping, storage, and manufacturing, not primarily from the soil or the beans’ natural environment. |
Key implications
This study demonstrates that while Nigerian cocoa beans are inherently low in lead, significant contamination occurs predominantly after harvest, during shipping, and processing. For heavy metal certification programs, it is critical to monitor and control post-harvest and manufacturing stages, as these are the primary points where lead contamination is introduced, often from industrial sources. Emphasizing supply chain traceability and stringent industrial hygiene is essential for reducing lead exposure in cocoa-based products, protecting vulnerable populations, and achieving compliance with international safety standards.
Citation
Rankin CW, Nriagu JO, Aggarwal JK, Arowolo TA, Adebayo K, Flegal AR. Lead Contamination in Cocoa and Cocoa Products: Isotopic Evidence of Global Contamination. Environmental Health Perspectives. 2005;113(10):1344-1348. doi:10.1289/ehp.8009
Lead is a neurotoxic heavy metal with no safe exposure level. It contaminates food, consumer goods and drinking water, causing cognitive deficits, birth defects and cardiovascular disease. HMTC’s rigorous lead testing applies ALARA principles to protect infants and consumers and to prepare brands for tightening regulations.
