Elemental Composition of PM2.5 in Shiprock, New Mexico, a Rural Community Located Near Coal-Burning Power Plants and Abandoned Uranium Mine Tailings Sites

Fine particulate matter (PM_2.5) was collected in Shiprock, New Mexico, a small community located near two coal–fired power plants and numerous abandoned uranium mine tailing sites. Eleven PM_2.5 samples were collected for 96 h over three sampling periods (April/May 2009, November 2009, and October/November, 2010). Nine samples were analyzed for 64 elements using inductively coupled plasma–mass spectrometry. B, Bi, Cu, Pb, Sb, Sn, and Zn were observed in at least eight samples at levels indicative of anthropogenic enrichment (enrichment factors between 30 and 650). All the seven elements could be explained by coal–combustion processes. B, Bi, and Sb are enriched in coals; Cu, Pb, Sn, and Zn are chalcophile–lithophile or chalcophile elements, all with appreciable affinity for sulfur, a component of coal. Principal component analysis also supported these findings. Four major sources (percent variance) were identified: soil (61%), coal combustion (17%), industrial (11%), and sea salt (5%). Concentrations of elements associated with coal combustion in Shiprock were lower than levels observed in other industrially influenced cities. This was explained by Shiprock’s location west of the power plants. Back trajectories indicated that winds arrive to Shiprock from the W, SW, and NW, but the power plants are located to the east (upwind) of the city. Samples were also analyzed for uranium (0.002–0.02 ng/m³) and other metals associated with mine tailings (Sr, Mo). All metals were detected but at low levels, and concentrations did not vary predictably with wind direction. Hence, the tailings sites could not be attributed as the source.