Temporal entry of pesticides through pollen into the bee hive and their fate in beeswax.

Honey bees are often exposed to a variety of contaminants, including pesticides from agricultural use. The aim of this study was to investigate the temporal entry of pesticides into the hive by examining the seasonal timing of honey bees bringing pesticide-contaminated pollen into their colonies and the subsequent accumulation of these pesticides in beeswax. Pollen and beeswax samples were collected biweekly from five colonies situated in an agricultural environment in Switzerland. In pollen, 23 pesticides (out of 50) were quantified, including 4 insecticides, 4 herbicides, 12 fungicides, a transformation product, an acaricide, and a synergist. The maximal insecticide concentration levels measured in individual pollen samples were 69.4 μg/kg (thiacloprid), 48.3 μg/kg (acetamiprid), 13.8 μg/kg (spinosad), and 11.1 μg/kg (indoxacarb), while fungicide levels ranged up to 2212.7 μg/kg (cyprodinil), and herbicides were up to 71.9 μg/kg (prosulfocarb). Eighteen of the pesticides found in pollen were also quantifiable in beeswax. Among these were 17 lipophilic pesticides with logarithmic octanol water coefficients (log Kow) equal or above 2.5, which showed similar temporal profiles and order of accumulation magnitude as in pollen. For example, maximal concentrations measured in individual beeswax samples were 12.4 μg/kg for indoxacarb (insecticide), 986.4 μg/kg for cyprodinil (fungicide), and 21.6 μg/kg for prosulfocarb (herbicide). Furthermore, pesticides with log Kow between 2.5 and 7.0 remained in the beeswax during wax purification. Our study shows that a large variety of pesticides brought into the hive through pollen potentially stay in the beeswax during recycling, thus constantly exposing honey bees to pesticides.