Honeybees and their products as bioindicators for heavy metal pollution in Malta

In this study, honeybees, propolis, air, soil and plant samples were gathered from two contrasting sites Ħal Luqa (industrial area) and L-Imġarr (agricultural area) in mainland Malta. Superficial heavy metals were extracted from the samples and tested using microwave plasma-atomic emission spectrometry in order to determine the concentrations of Ag, As, Cd, Cr, Cu, Pb, Sn, Zn, Ni and Hg. The honeybee and propolis samples were digested using nitric acid and hydrogen peroxide and then ashed using a muffle furnace in order to prepare mineral solutions. Simultaneously the air samplers, soil and plant samples were washed using de-ionised water in order to extract the heavy metals settling on sample surfaces. Different methods of filtration were used in order to extract the metals from the surfaces of the samples. The most abundant metals in honeybees and propolis, and on plant and soil samples, were Sn and As (p<0.0001). In air samples0, the most abundant metal was Pb followed by Sn (p<0.05). These findings indicate that the honeybee and its propolis are good indicators for Sn and As contamination.