**3. Metals in honey**

The presence of metals in honey has been associated with the presence of hives close to contamination sources, such as factories, highways, volcanoes, or mines/mine tailings. Contamination sources can also include agrochemicals that contain cadmium and arsenic, among others [30–32]. Due to this association, extensive research has been conducted in honey to determine the relationship between heavy metal contents and quality indicators or biological markers [33, 34]. Frequently, heavy metal concentrations in honey are low, complicating the analysis of these elements. This complication is directly evidenced in the quality of obtained results, where any loss during the analytical processing of samples influences the concentration values determined for each metal [35].

Related to the analysis of honey, Przybyłowski and Wilczyńska [36] conducted research on polyfloral honey produced in Poland to evaluate possible relationships between parameters such as pH, the glucose:fructose ratio, moisture, electric conductivity, and hydroxymethylfurfural concentration, among others, and the presence of cadmium, lead, and zinc. These relationships were determined based on methodologies established by the Association of Analytical Communities [37] for processing organic samples and performing posterior metal assessments. While no clear relationships were found between the measured parameters and the metals studied, discrete cadmium and lead concentrations were found in all of the studied samples. This finding indicates a degree of environmental contamination. Similarly, relationships did exist between plant origin and the presence of zinc in samples. Further research was conducted by Hernández et al. [38], who analyzed the metal contents in 81 honey samples from the Canary Islands and compared results against 35 additional samples from zones in Spain and Europe in general. Analyses established that the concentrations of alkaline and alkaline earth metals were within specific ranges that discriminated between Canary Islands and European mainland honey. The authors therefore concluded that this type of analysis can be used to certify the source of a honey. Hernández et al. [38] also suggested that the presence of metals could indicate the production of honey in areas contaminated by these metals.

Another study on avocado honey from Spain also showed a common pattern between the measured concentration of alkaline and alkaline earth metals. Just as with the Cannery Island honey, Terrab et al. [39] suggested that honey origin could be established based on the concentrations of certain metals. However, the correlation between botanic origin and the presence of metals has been difficult to establish in other parts of the world. For example, Fredes and Montenegro [40] studied the possible origin-metals correlation for honey from distinct regions of Chile, but were unable to establish an association between the presence of the measured elements and the botanic/geographic origin of the analyzed honey samples.

On the other hand, an objective established by a number of researchers has been to correlate the presence of metals with the biological properties of honey. One such investigation by Küçük et al. [41] analyzed three honey samples with different botanic sources in Turkey to evaluate a possible relationship between the concentrations of alkaline, alkaline earth, and other metals with the antibacterial properties of honey. The obtained results were able to establish that honey with higher concentrations of all the studied metals also presented greater antibacterial activities. In the three samples, the metal concentrations did not exceed permitted limits. Nevertheless, no clear link was found between the measured metal concentrations and other biological properties of honey, such as phenolic compound levels.
