Lead in Chocolate

Prop 65

Lead (Pb) has been an environmental concern for many years. The concern has most recently focused on drinking water, plumbing fixtures, calcium based supplements and antacids, PVC plastics, brass keys, and now ...... Chocolate. NBC News in Los Angeles reported the story.

The California legislation known as Prop 65 has set a "safe harbor" limit for lead at 0.5 ug/day. The concern over Pb in chocolate is articulated in a Fact Sheet published by the American Environmental Safety Institute. AESI proposes a limit of 0.02 ug/g Pb in chocolate.

Curiously, cocoa beans are naturally very low in lead. So the source of lead in cocoa products is under investigation. For more information see EHP, Vol 113, Oct, 2005.

Pb Testing

We have developed test procedures for trace amounts of Pb in a variety materials using ICPMS. This procedure uses an analytical technique called isotope dilution - ICPMS (inductively coupled plasma-mass spectrometry).

Lead (Pb) has 4 naturally occurring isotopes: ²⁰⁴Pb (1.4%), ²⁰⁶Pb (24.1%), ²⁰⁷Pb (22.1%), and ²⁰⁸Pb (52.4%). The numbers in superscript represent mass of the lead isotope while the numbers in parenthesis represent the % of each isotope in naturally occurring Pb. We actually separate each of the isotopes using a mass spectrometer when we test for Pb using ICPMS.

To approximately 5 g of chocolate is added an accurately measured amount of Pb enriched in ²⁰⁴Pb. This is added

as an isotope dilution standard, but more on that later. The chocolate is then ashed at a relatively low temperature, the residue is then dissolved in nitric acid, and the solution analyzed for Pb by ICPMS. Chocolate drinks are dissolved in a slightly different solution for analysis. The detection limits in chocolate are generally less than 0.001 ug/g.

The response of trace amounts of Pb in ICPMS will vary with interferences from the sample. For that reason an internal standard is normally used to correct for sample to sample variations in Pb response. In this case, the internal standard is ²⁰⁴Pb, i.e. an isotope dilution standard. In theory, using an isotope dilution standard to correct for variations in response due to sample matrix interferences is the most accurate method for quantifying trace amounts of Pb.

For a quotation......

While we perform Pb in blood and urine, we suggest that consumers contact their physicians.

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