The intent of this study was to provide information necessary to characterize the present concentrations of an emerging transportation related contaminant, the platinum group metals (PGM), and to provide background information necessary to explore the potential uses of these metals as a specific marker of transportation related contamination that results from the discharge of road runoff into streams. Thirty-seven road crossings were evaluated in the Atlantic Slope of central North Carolina. Mussel tissue and sediment samples were collected from upstream and downstream of each road crossing. Samples were analyzed for the platinum group metal platinum (Pt), as well two other common transportation pollutants, lead and cadmium, and a common atmospheric pollutant, mercury. The enrichment of pollutants (downstream concentration ¿ upstream concentration) was compared to the number of vehicles crossing the stream. Local stream environmental variables and landscape scale variables were used to model the concentration of Pt in mussel tissue. Two 28-day laboratory toxicity tests, one with Pt and one with Pb, were conducted to assess the potential threat that current concentrations of these metals pose to native mussel fauna.
The correlation of enrichment of the metals at bridge sites was weak for all metals studied. We hypothesize that complex hydrologic alteration caused by highway crossing structures was responsible for increased variation in downstream samples. Multiple samples taken from a single stream over an 8 km stream reach indicated that Pt concentrations in mussel tissue and sediment was enriched downstream of a road crossing, but the enrichment was not uniform and enrichment does not peak for several km downstream from the source. Results from the 28-day tests indicated that PGM may not pose an immediate threat to adult mussels and that mussels are a good sentinel species for studying PGM.
