Maltese honey as a bioindicator of atmospheric heavy metal pollution in Malta

Abstract

In this study, superficial concentrations of heavy metals (Cd, Cr, Cu, Pb, Sr, Zn) in air, soil, and plants; biological and superficial concentrations in honeybees, honey, and wax samples from two Maltese localities (one urban and one rural) were analysed. Correlations between the heavy metal contents of the different samples collected from both localities were determined to adopt a holistic environmental approach to atmospheric heavy metal pollution. Additionally, physicochemical characteristics of honey (indicative of honey quality) were determined and correlated with the heavy metal contents in wax and honey, to understand whether wax and honey produced by honeybees in Maltese rural and urban areas can be used as bio-indicators of atmospheric heavy metal pollution. Cr and Pb were the most prominent metals in air, soil, and plants; while Zn, Pb, and Cu were the most abundant metals in honeybees, honey, and wax. Moreover, the honeybee was found to be a good indicator for Zn and Cu in air, whereas wax (and honey) is a good indicator for Pb in soil, superficially. Furthermore, Zn and Sr resulted as Air-Plant-Bee and Soil-Plant-Air contaminants, respectively. Cr and Cu were not transferred to bee products although being present in specific matrices. Honey quality was not compromised through diastase (positive correlation with metals), but rather through proline (negative correlation with metals), which makes it a potential indicator of honeybee morbidity and mortality. In fact, it was found that heavy metals, particularly Sr, affect honeybees’ health. However, although being adversely affected by toxic heavy metals, honeybees were still found to incorporate proline within honey.