Trace Element Composition of Municipal Waters in the United States: A Comparison of ICP-AES and ICP-MS Methods

A collaborative project was outlined by representatives of the Nutrient Data Laboratory and the Food Composition Laboratory of the United States Department of Agriculture. The purpose of the project was to obtain trace element (Ca, Cu, Fe, Mg, P, K, Na, Mn, Zn, Co, Cr, Ni and V) composition data for municipal waters sampled around the United States during three different seasons. Several sub-goals were outlined: (1) Compare inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) methods for the direct determination of nutritionally important elements in water; (2) Compare data from this study with a national, probability-based sampling plan, to existing published data in U.S. Department of Agriculture's Standard Reference Database SR-13; (3) Consider the variability of values comparing different locations; (4) Evaluate seasonal variability; (5) Conclude as to whether or not this high consumption product is a reasonable source of trace elements in the human diet. Results from the study indicated that the excellent detection capability of ICP-MS provided Cr, Ni and V results at the ppb level and also provided P and K data, all of which will be significant positive additions to USDA's Standard Reference Database SR-13. Correlation studies comparing ICP-MS and ICP-AES data showed excellent agreement (Ca, Cu, Mg, Na R=0.99+; K R=0.96). No real significant seasonal variability was identified during the course of the study. This study highlighted the fact that water is not a significant source of most trace elements in the U.S. diet.