A Preliminary Evaluation of Honeybees as Bioindicators of Heavy Metal Pollution in NE Ireland

Heavy metals pose a substantial risk to the health of humans, animals, and plants. They are naturally occurring, but anthropogenic activities have released concentrated and sometimes toxic levels as a result of industrial activities. These pollutants can enter the food web and bioaccumulate in different animal and plant species causing sickness and death. Five commonly occurring heavy metals in Ireland, cadmium, chromium, copper, lead and zinc were assessed using honeybee bioindicators; pollen, honeybees themselves and honey. All samples were gathered from within hives to investigate whether heavy metal pollutants are entering the environment and being bioaccumulated to levels which might affect food webs. Such honeybee foraged sampling was carried out at two potentially polluting industrial sites in NE Ireland; an operational lead/zinc mine, and an intensively managed apple orchard. A site at an organic tillage farm was also sampled. Cadmium was found in very low abundance at all sites, even the mining site. Unsurprisingly, lead concentrations were highest at the mining site. Zinc was also expected to occur in highest concentrations at the most industrialised site, though concentrations were similarly high at all sites, though at lower than toxic concentrations, apart from the pollen samples which were found to exceed food-safety threshold levels. Honeybees appeared to act as biofilters for chromium, reducing the concentrations found in honey compared with what was detected in foraged pollen. All honey samples were found to have safe levels of heavy metal constituents, even from the mining site. The use of honeybee colonies appears to be a useful approach to sampling landscape-level metal contamination. In addition, as lead concentrations were found to be lowest in honey from the mining site, the approach involving analysis of several hive products identifies a role for honeybees in biofiltering some of this contaminants.