Cerium(IV) oxide nanoparticles induce sublethal changes in honeybees after chronic exposure
High annual production and use of cerium (IV) oxide nanoparticles (nCeO2) may lead to their atmospheric release and substantial deposition on plants. This poses potential threat to pollinators. We investigated the effects of nCeO2 spiked food (2-500 mgL-1) on summer and winter honeybees Apis melifera carnica after chronic 9 days oral exposure. Acetylcholinesterase (AChE) and glutathione S-transferase (GST) activities were measured in different body compartments (heads, thoraces, and haemolymph). Activity of AChE was assessed in salt soluble (SS) (containing soluble and membrane AChE) and detergent soluble (DS) fractions (predominately membrane-bound AChE). Exposure of honeybees to nCeO2 spiked food had no significant effects on survival up to 500 mgL-1 (<10%), while significant biochemical alterations were evidenced already at 2 mgL-1. In summer honeybees a significant increase in activities of AChE in SS fraction and GST was found, while AChE activity in DS fractions was decreased at nearly all exposure concentrations. Exception was the 250 mgL-1 exposure, where AChE activity in DS fractions was increased. The alteration of AChE in DS fraction could be symptomatic for the affected neuronal system, while alterations of GST activity indicate detoxification processes. Apparent difference in response to nCeO2 was evidenced between the summer and winter honeybees, which is in line with their different physiology. We ascribe most of the observed effects to particulate nCeO2 because negligible presence of Ce ions species were found in the food. We conclude that nCeO2 release into the environment, especially atmospherically deposited material, is a potential risk to honeybees.