EVALUATION OF TRACE METAL POLLUTION ASSOCIATED WITH TRAIN TRAFFIC IN THE PACIFIC NORTHWEST

Train traffic is anticipated to increase in the Pacific Northwest to meet growing demands for coal and oil in Asia. Additional train traffic will increase toxic trace metal contamination along train routes, including in protected national forests and state parks such as the Columbia River Gorge National Scenic Area (CRGNSA). Lichens are environmental archives of atmospheric metal deposition. Metal concentrations and Pb isotopic compositions of lichen samples collected along coal train lines can be used as indicators of anthropogenic metal pollution associated with trains: from the combustion of diesel fuel, moving metal parts, and cargo (e.g., open cars of coal).

To evaluate the impact of train metal emissions on surrounding natural areas, lichen samples were collected at increasing distances along perpendicular transects to the rail line. These lichen samples were measured for metal concentrations using ICP-MS and for Pb isotopic compositions using MC-ICP-MS. Our study found elevated metal concentrations near rail lines that generally decreased with increasing distance from rail lines. These elevated levels are comparable to those found near major roads (e.g. highways, interstates). Elevated levels of Ni, Cr, Cu, Pb, and Zn are largely attributed to material abrasion of train parts, and combustion of diesel. In contrast, elevated As may result from coal dust lost from transportation in open cars. Arsenic levels at sites closest to the rail were up to three times higher than As levels at sites farthest from the rail. Lichens collected near a coal-fired power plant in Boardman, OR are indicators of high N pollution and were notably deformed, presumably from pollution effects. Trace metal concentrations in Boardman were significantly higher than other areas in the CRGNSA, especially in lichens collected along the railroad tracks.

Rail car abrasion, train cargo, and nearby roads can contribute to elevated metal concentrations near railroads. Lead and S isotope ratios will be used to fingerprint sources of these elements and determine their relative contributions. Future comparative studies on rail lines where coal is not transported and on rail lines closer to coal mines, where coal is loaded onto trains, may help to distinguish between the importance of the diesel fuel and coal dust as sources.