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Charley W. Rankin,¹ Jerome O. Nriagu,² Jugdeep K. Aggarwal,³ Toyin A. Arowolo,⁴ Kola Adebayo,⁵ and A. Russell Flegal¹

¹Environmental Toxicology, WIGS,University of California, Santa Cruz, California, USA; ²Department of Environmental Health Sciences, School of Public Health, University of Michigan, Ann Arbor, Michigan, USA; ³Earth Sciences, University of California, Santa Cruz, California; ⁴Department of Environmental Management and Toxicology, and ⁵Department of Agricultural Extension and Rural Development, University of Agriculture, Abeokuta, Nigeria

Abstract
In this article we present lead concentrations and isotopic compositions from analyses of cocoa beans, their shells, and soils from six Nigerian cocoa farms, and analyses of manufactured cocoa and chocolate products. The average lead concentration of cocoa beans was ≤ 0.5 ng/g, which is one of the lowest reported values for a natural food. In contrast, lead concentrations of manufactured cocoa and chocolate products were as high as 230 and 70 ng/g, respectively, which are consistent with market-basket surveys that have repeatedly listed lead concentrations in chocolate products among the highest reported for all foods. One source of contamination of the finished products is tentatively attributed to atmospheric emissions of leaded gasoline, which is still being used in Nigeria. Because of the high capacity of cocoa bean shells to adsorb lead, contamination from leaded gasoline emissions may occur during the fermentation and sun-drying of unshelled beans at cocoa farms. This mechanism is supported by similarities in lead isotopic compositions of cocoa bean shells from the different farms (²⁰⁶Pb/²⁰⁷Pb = 1.1548-1.1581 ; ²⁰⁸Pb/²⁰⁷Pb = 2.4344-2.4394) with those of finished cocoa products (²⁰⁶Pb/²⁰⁷Pb = 1.1475-1.1977 ; ²⁰⁸Pb/²⁰⁷Pb = 2.4234-2.4673) . However, the much higher lead concentrations and larger variability in lead isotopic composition of finished cocoa products, which falls within the global range of industrial lead aerosols, indicate that most contamination occurs during shipping and/or processing of the cocoa beans and the manufacture of cocoa and chocolate products. Key words: chocolate, cocoa, contamination, isotopes, lead, natural foods. Environ Health Perspect 113: 1344-1348 (2005) . doi:10.1289/ehp.8009 available via http://dx.doi.org/ [Online 26 May 2005]

Address correspondence to C.W. Rankin, WIGS Laboratory, ETOX Department, UC Santa Cruz, 1156 High St., JBEB 269, Santa Cruz, CA 95064 USA. Telephone: (831) 566-8981. Fax: (831) 459-2088. E-mail: rankin@etox.ucsc.edu

R. Franks, S. Hibdon, D. Steding, and the WIGS laboratory were instrumental in completing the research. We thank P. Mascharak, D. Smith, Z. Zhu, and the anonymous reviewers for their suggested revisions of the manuscript.

This study was funded by the W.M. Keck Foundation, University of California Toxic Substances Research and Teaching Program, and the American Environmental Safety Institute.

The authors declare they have no competing financial interests.

Received 10 February 2005 ; accepted 26 May 2005.