Reference values for essential and toxic elements in human milk.

Dependable reference values (RVs) for the concentration ranges of health-related elements in human biological fluids and organs are to date of acknowledged importance for an early recognition of pathological states. On the other hand, the present lack of reliable data on levels to be considered as baseline values for elements of major concern from a toxicological, environmental and nutritional point of view demands the development of experimental procedures capable of satisfying the requirements of detection power, specificity and applicability on a large scale necessary to generate vast amounts of reliable measurements. As part of an overall monitoring program, an investigation was undertaken with the following two aims: a) the present suitability of inductively-coupled plasma atomic emission spectrometry (ICP-AES) to identify and quantitate minor and trace elements in human milk with the necessary accuracy and precision; b) assessment of RV concentrations for Al, Ba, Cd, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb and Zn. Four population groups were selected (each with 9 subjects) resulting from the various combinations of smokers and non-smokers from an urban or a rural environment. Strict eligibility criteria were adopted in order to select only women in good health, no known occupational exposure and whose nutritional habits could be described in detail. A scrupolous and systematic approach was adopted to minimize every possible source of elemental contamination from the sampling step onwards. Digestion of samples was attempted both with mixtures of strong acids and by resorting to acid-assisted mineralization in a microwave oven. Both methods were satisfactory for subsequent introduction into the torch of the ICP-AES system. The outcome of this pilot study gave the following median RVs for concentration (in mg/kg): Al, 0.14; Ba, 0.013; Cd, 0.002; Cr, 0.016; Cu, 0.40; Fe, 0.72; Li, 0.004; Mg, 29.4; Mn, 0.006; Ni, 0.05; Pb, 0.016; and Zn, 3.08.