Barn swallow (Hirundo rustica) transfers current-use pesticides from agricultural fields to houses

Barn Swallows (Hirundo rustica) forage in fields and nest in houses, and thus they can act as biological vectors for the transfer of pollutants from fields to houses. The present study measured current-use pesticides (CUPs) in water, soil, insects, swallows, guano, and indoor dust with and without guano contamination, and investigated the transfer of pesticides from agricultural fields to houses through food chains and guano deposition. The median concentrations of all CUPs were 2.47 ng/mL in water and 35.8, 2.80-17.5, 4.51, 16.1, 8.29, and 8.75 ng/g dry weight in soil, insects, swallows, guano, and indoor dust with and without guano contamination, respectively. The biomagnification factors of CUPs were generally lower than 1, due to the efficient metabolism of CUPs by organisms. The more hydrophobic CUPs were less bioavailable and prone to transfer from insects to guano. Most pesticides showed comparable or higher concentration values in guano-contaminated dust than those in dust without guano contamination. The ratios of pesticide levels in guano-contaminated dust to those in dust without guano contamination were negatively and significantly correlated with soil half-lives of pesticides (p < 0.01). Guano likely inhibits the degradation of pesticides in dust, such as microbial degradation, by changing the dust contents. These results proved that pesticides were transferred from agricultural fields to houses via barn swallows, raising concern for greater exposure risks for country residents.