Polyaromatic hydrocarbons and elements in sediments associated with a suburban railway.

Railroad operations are a potential source for contamination of aquatic ecosystems. We examined concentrations of polyaromatic hydrocarbons (PAHs) and selected elements in sediments collected during 2009-2011 from streams, ditches, or ponds bisected or bordered by the former Elgin, Joliet, and Eastern rail line in the western Chicago, Illinois, metropolitan area. Summed PAH concentrations were greater in sediments collected downstream than in those collected upstream of the railroad and were negatively associated with distance within 500 m of the tracks. Phenanthrene and dibenzo (a,h)anthracene concentrations at some locations exceeded probable effect thresholds for risks to aquatic life. Although maximum levels of chromium (Cr) were below levels of concern, we did not determine the valence state of Cr; thus, risks to aquatic life could not be fully evaluated. Nickel and mercury concentrations exceeded lower effect levels, and vanadium concentrations exceeded chronic toxicity thresholds at some locations, although we did not detect an association between these elements and the presence of the railroad. Lead and arsenic concentrations were greater in proximity to the railroad; however, concentrations were below thresholds of concern for aquatic life. Our results suggest that the railroad and associated activities are contributing some environmental contaminants to waterways in close proximity to it, particularly in a downstream direction. Risks to aquatic life may be greater than implied by observed concentrations of individual contaminants, as synergistic adverse effects are likely to occur with exposure to complex mixtures.