Newswise — Sources ranging from soil contamination to industrial activities may account for high lead concentrations found in some manufactured cocoa products, according to a study published today in the October issue of the peer-reviewed journal Environmental Health Perspectives (EHP). Researchers seeking to understand why lead concentrations of manufactured cocoa products are among the highest of all foods found that cocoa beans, the main ingredient in chocolate, have some of the lowest reported lead levels for any natural food.

To determine the source(s) of lead in manufactured cocoa products, researchers studied the lead isotopic composition of cocoa beans and shells from six cocoa farms in the three highest-producing states in Nigeria, where much of the world's cocoa supply originates. Scientists homogenized bean and sediment samples to make composites for soil, beans, and cocoa bean shells for each farm. By studying the isotopic compositions, researchers sought to better determine if soil or farm sources were contributing to lead contamination in cocoa products.Results for lead concentrations in the cocoa beans themselves were low, averaging 0.512 nanograms per gram (ng/g), among the lowest lead concentrations reported for any food. The average concentrations found in the cocoa beans shells, however, was about 320 times higher (160 ng/g).

Because soils showed a range of isotopic compositions overlapping those of the shells, the study authors suggest that the soil may cause only a small degree of the contamination. The narrower range of isotopic composition in the shells, however, suggests a more singular source of contamination other than soil.

"Similar lead isotopic composition in contaminated cocoa bean shells from Nigeria, together with the high ability of cocoa bean shells to adsorb lead, suggest that contamination during cocoa processing at each farm may be responsible for some of the contamination in cocoa products, and it is proposed that the ongoing use of leaded gasoline in Nigeria contributes to that contamination," the authors wrote.The researchers also compared the cocoa beans with finished cocoa products. Results showed much higher lead concentrations, as well as greater variability in the isotopic composition, among the finished products.

The results suggest that the majority of lead contamination occurs after the beans are harvested, dried, and shipped from the farm. The presence in the samples of lead isotopes found in industrial emissions around the world indicates that industrial activities should be studied as a potential source of contamination."Further studies investigating bean storage and intermediate phases of shipping and processing are needed to isolate the predominate source of lead found in the chocolate and cocoa products," the authors wrote.

The lead author of the study was Charley W. Rankin of the Department of Environmental Toxicology at the University of California, Santa Cruz. Other authors included Jerome O. Nriagu, Jugdeep K. Aggarwal, Toyin A. Arowolo, Kola Adebayo, and A. Russell Flegal. Funding for the research was provided by the W.M. Keck Foundation, University of California Toxic Substances Research and Teaching Program, and the American Environmental Safety Institute. The article is available free of charge at

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at Brogan & Partners Convergence Marketing handles marketing and public relations for EHP, and is responsible for creation and distribution of this press release.

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Environmental Health Perspectives (Oct-2005)