Rubidium and Lead Content of Market Milk

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Abstract
Market milk samples collected on a quarterly basis from various cities in the United States were analyzed for rubidium (Rb) and lead (Pb) content by atomic absorption spectrophotometry. The average Rb content of milk varied between 0.57 and 3.39 ppm. Statistical analysis of the data showed that the Rb content of milk varied significantly from one city to another at [alpha] = 0.01; in addition, milk from cities in southeastern United States showed significant differences from one sampling period to another. In general, the Rb content of milk sold in cities in inland states was small and that in cities of coastal states large. The average Pb content of milk varied between 0.023 and 0.079 ppm, and the national weighted average was 0.049 ppm. The Pb content of milk did not vary significantly from one city to another. Only in milk from southeastern states was a significant difference noted from one sampling period to another. Analysis of 76 milk samples from individual cows raised on farms serving the Cincinnati area showed Pb content varied from 0.009 to 0.212 ppm, with an average of 0.047 ppm.