Introduction
Many elements present in the crust of the earth show important functions for living organisms, being essential for their development even in small quantities. Plants absorb part of their inorganic nutrients from the soil, absorbing them through various mechanisms.1 Many of these elements can cause disease or intoxication in concentrations just slightly higher than the concentration necessary for a healthy life. Heavy metals, on the other hand, show high toxicity, even at very low concentrations. Some kinds of metals of common use can cause severe processes of intoxication, such as chromium. Its accumulation in the organism can lead to the formation of carcinomas.2 In excess, copper leads to diseases like Menks Syndrome's and Wilson's disease, both showing cellular degeneration in the human organism.3
The presence of metals in medicinal plants must be studied due to the possibility of intoxications from ingesting their extracts, infusions or teas, or even through cutaneous absorption during the healing of wounds.4,5 In traditional oriental medicine, like Ayurvedic (Indian) and Chinese medicines, the insertion of heavy metals in the medicinal preparations is very common, bringing on many cases of intoxication by lead, arsenic and mercury.6 The determination of metals in plants is not common in Brazil, but in a recent study, samples of boldo (Peumus boldus Mol.) from Brazil, Chile, and Argentina were analysed by atomic absorption spectrometry allowing the quantification of iron, manganese, copper and zinc while lead, chromium and cobalt were not detected.7
Atomic absorption spectrometry is a quantitative but monoelemental technique, allowing the determination of only one (or a few, in certain instruments) elements at a time. Energy Dispersive X-Ray Fluorescence (EDXRF) using a lithium-silicon detector is a multi-elemental technique in which a unique qualitative analysis provides data about all the elements present with an atomic number between 11 and 92, that is, between sodium and uranium.8,9
Among the natural products of medicinal utilization the oleoresins and, among these, the resins produced by the Burseraceae, one of the most important resin producer families, stand out. This oleoresin is widely utilized in ethnopharmacology for diverse applications, e.g. to heal wounds, as an analgesic and antiseptic.10 They are additionally used for cosmetics and perfumes, even being utilized as food in the Amazon Region.11,12 Monoterpenoids and triterpenoids were described as the organic compounds of these oleoresins.12 Only one paper has recently been published describing the inorganic composition of this family, which concerns stems of Bursera microphylla that was collected in Mexico. Macronutrients such as Ca, P, Mg, Na and K were described, in addition to the micronutrients Mn, Cu, Fe and Zn.13
In the Negro and Solimões river basins, there is a great endemism of the Burseraceae family, a great variety of minerals in the soil are encountered, including elements that are able to induce to intoxications. Chromium, for example, is described as a component in tourmaline and quartz. Manganese is found in grenades and as a component in staurolites, and zirconium is found in abundance in the Amazonian soil in the zircon (ZrSiO4) mineral.14-16
In Brazil, there are specific laws that control the presence of metals in commercialized natural products. Bioactive oils and plant extracts commercialized as personal hygiene products, cosmetics and perfumes must be free of As, Pb, Cr, Cd, Te, Ta, and Sb. In food, there are maximum limits for the following elements: As, Pb, Cd, Sn, Cu, and Hg. The methodology for analytical quality control that will be applied to detect heavy metals must also be indicated for phytotherapic registration.17
Despite the necessity of determination of those metals in phytotherapics, cosmetics, food and perfumes, data about this is rare in the scientific literature. For the products of Amazonian biodiversity, studies that describe the inorganic composition and that are able to orient the methodologies of quality control are even rarer. In an attempt to contribute to the understanding of the inorganic composition of the oleoresins from the Burseraceae family, five Amazonian species had their resins analyzed by EDXRF.