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Medicinal plants originating from different natural locations in Northern Poland representing four different plant species: Betula pubescens Ehr., Achillea millefolium L., Urtica dioica L. and Hypericum perforatum L. were analysed. The aim was to determine the contents of P, N, Fe and Zn in these medicinal plants, and to assess the bioavailable inorganic forms of these elements obtained by aqueous extraction. The concentrations of total P and N and their extractable species were determined in mg g À 1 of dry plant weight (dry wt), and the concentrations of N -NO 3 , Fe and Zn and their extractable species in the range of mg kg À 1 of dry wt. In all birch leaf samples, the maximum amount of total and extractable Zn was found, whereas the highest total and extractable concentrations of N, P and Fe were obtained in nettle herbs. Statistically significant correlations between 13 pairs of total and extractable forms of studied elements were found. Principal component analysis of the experimental data allowed differentiation of the plant material based on its elemental contents, and identified total P and Zn and its extractable forms, as the crucial factors responsible for that differentiation. Comparison with the dietary reference intakes showed that the plant materials are poor sources of bioavailable P, Fe and Zn, and that contents of nitrates do not exceed the acceptable daily intakes norms.

The presence of mercury in the living cells may be caused by environmental pollution with this element, which is referred to as a toxic xenobiotic. Many literature reports have provided evidence for toxic effects of low levels of mercury in the human body. Therefore, it seems essential to investigate mercury content in food and in natural environment, particularly its seasonal variations. The objective of this study was to determine trace amounts of mercury in 45 samples of 20 medicinal plant species collected in northern Poland, in various seasons of the year, i.e., in autumn 2012 and then spring 2013. The results obtained showed that the levels of mercury in the herbs were lower in spring (3.66–34.89 ng/g) than in autumn (4.55–81.54 ng/g). The statistically significant correlation (p < 0.05) between the levels of mercury in herbs collected in spring and autumn indicates hazardous accumulation of the element in plants in autumn. The highest levels of mercury were found in leaves and plants growing in the vicinity of busy streets. Perennials plants have a significantly higher mercury levels as compared to those of monocarpic plants. Furthermore, commonly used herbal plants have a significantly higher mercury levels as compared to those less common.

The concentrations of seven macro- and microelements (K, Mg, Ca, Na, Fe, Zn, Mn) in 59 herbs (herbs, leaves, flowers, fruits, roots), which are commercially available and frequently used in Poland for medical purposes as well as in their water extracts (infusions and decoctions), were determined after microwave mineralization. The data obtained show that all herbal raw materials analysed contain macroelements in the range of mg g−1 on d.w. whereas microelements in the range of mg kg−1 on d.w. and that elemental concentrations varied widely. On the basis of a comparison of concentrations of elements in herbal raw materials examined and water extracts prepared from them, the extraction efficiency was expressed as a percent of the total content of each element present in the infusion or decoction. The percentages of macro- and micro- elements leaching from different morphological parts of plants into water extracts varied across a wide range of values, from 1% in the case of Na to 56% in the case of K. Real daily intake of the macro- and microelements elements through one cup of infusions or decoctions were shown that water extracts from herbal raw materials are not an important source of bioelements in human diet.