Low Dietary Levels of Al, Pb and Cd May Affect the Non-enzymatic Antioxidant Capacity in Caged Honey Bees (Apis Mellifera)

Several hypotheses have been proposed to explain the abnormally high mortality rate observed in bee populations in Europe and North America. While studies based on the effects of pesticides are paramount, the metals present in agroecosystems are often overlooked. Sources of metals are linked to the nature of soils and to agricultural practices, namely the use of natural or chemical nutrients as well as residual materials from waste-water treatment sludge. The aim of this study was to investigate the effects of metals on honey bees exposed for 10 days to environmentally realistic concentrations of Al, Pb and Cd (dissolved in syrup). The monitoring of syrup consumption combined with the quantification of metals in bees revealed the following order for metal bioconcentration ratios: Cd > Pb > Al. Alpha-tocopherol, metallothionein-like proteins (MTLPs) and lipid peroxidation were quantified. When bees were exposed to increasing amounts of Cd, a marked augmentation of MTLPs levels was found. Lead (Pb) and Cd caused an increase in α-tocopherol content, while alteration of lipid peroxidation was observed only with Al exposure. These findings raise concerns about the bioavailability and the additional threat posed by metals for pollinators in agricultural areas while providing new insights for potential use of the honey bee as a sentinel species for metal exposure.