The biological effects of complex contaminant mixtures on tree swallow (Tachycineta bicolor) nestlings from the Great Lakes; Using omics techniques to evaluate and predict contaminant mixtures.


The effects of exposure to multiple environmental contaminants on Tree Swallows in Great Lakes Areas of Concern (AOCs) were investigated through a series of transcriptomic and metabolomic projects. Tree Swallows are ideal bioindicators for assessing contaminant exposures in birds from the Great Lakes region, and to examine the biological transport of environmental contaminants from aquatic sediments into terrestrial ecosystems. This study was carried out in collaboration with the United States Geological Survey (USGS) and funded by The Great Lakes Restoration Initiative. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), per- and polyfluoroalkyl substances (PFAS), and chlorinated pesticides were identified as the contaminants in the Great Lakes region most likely causing bird or animal deformities or reproduction problems. A combined omics approach was used to identify altered biological responses and functions, to prioritize contaminants, and to assess the risks of chemical mixtures on a regional scale in the Maumee Area of Concern (AOC) in Ohio, USA. This area includes wastewater treatment plants (WWTPs) and industrial land-use areas. Contaminant concentrations, including for many endocrine-disrupting chemicals, were found to be higher in Maumee Tree Swallows than from a remote reference site on Star Lake, Wisconsin, USA. There was an up-regulation of lipogenesis genes, biosynthesis of unsaturated fatty acids, and higher lipogenesis related metabolites at two industrial land-use sites, Ironhead and Maumee, relative to WWTP sites (Perrysburg and SideCut) and the reference site. Next, to evaluate effects on Tree Swallow nestlings exposed to PCBs, PAHs, PBDEs, or PFOS amid a complex mixture of environmental contaminants on a larger scale across the Great Lakes, altered functions and pathways associated with individual contaminant classes were determined. Predictive models were established using lasso regression to predict PCB and PAH concentrations in the nestlings with high accuracy rates. Avian gene panels have been developed recently to aid in ecotoxicological assessments, and they were used to characterize the biological effects of chemical mixtures and contaminated sites. Linear penalized models built with global gene expression were found to outperform targeted gene panels or bioindicators in predicting PCB or PAH concentrations.