Toxic metal(loid)s are commonly suspected impurities in food supplements, especially herbal ones.

This study aimed to analyze their presence in soy isoflavone supplements, represented by 21 products collected in the central Balkan countries (Serbia, Bosna and Hercegovina, Croatia) and tested by an inductively coupled plasma mass spectrometry technique after microwave digestion. The performance of the analytical method was monitored by the analyses of certified reference materials, as well as by the regular participation of an accredited laboratory in proficiency testing.

The elemental profiles consisted of 23 elements, most of which (18) were detected in more than half of the products, in extremely variable concentrations—in the case of Sr, Fe and Zn, over three orders of magnitude. The elements are classified according to the ICH Guidelines for Elemental Impurities. Regarding Class 1 elements (systemic toxicants causing multiple organ injuries/failure; limited/no use production of pharmaceuticals), the frequency of detection of As (91%), Pb (77%) and Cd (68%) was significantly higher than that of of Hg (41%). The highest concentrations of elements covered by Regulation (EU) 2023/915 complied with the maximum that was allowed (Pb 0.30 vs. 3.0 mg/kg, Cd 0.38 vs. 1.0 mg/kg, Hg 0.08 vs. 0.10 mg/kg). Class 2A elements (route-dependent toxicants; high probability of occurrence), Co, V and Ni, were found in all samples, in concentrations up to 1.37, 0.65 and 2.58 mg/kg, respectively. The Class 2B elements (route-dependent toxicants; low probability of occurrence) Se and Tl were rarely detected. The Class 3 elements (low oral toxicity) Ba and Cu were found in all, and Cr in all but one supplement, Sb in half and Sn in none. Among the non-classified elements (low inherent toxicity), Te, Be and Sr were detected.

Considering that toxic metal(loid)s can pose a serious concern for the health of consumers, the sources of such impurities (raw materials, production equipment, etc.) should be strictly controlled.