Heavy Metals in Mosses and Soils on
Six Transects Along the Red Dog Mine Haul Road, Alaska
Western Arctic National Parklands
National Park Service
Jesse Ford, Ph.D.
Linda Hasselbach, M.S.
The Red Dog Mine Haul Road traverses 24 miles of National Park Service (NPS) lands in Cape Krusenstern National Monument (CAKR), Alaska. Ore trucks use the road to transport 1.1 million dry tons of lead-zinc concentrate annually from the mine to a port site on the Chukchi Sea. In the summer of 2000, moss and soil samples were collected from six transects perpendicular to the haul road in CAKR. Laboratory analyses were performed on the moss Hylocomium splendens, soil parent material, road dust, and substrate from materials sites. Analysis revealed a strong road-related gradient in heavy metal deposition. H. splendens was highly enriched in lead (Pb > 400 mg/kg), zinc (Zn > 1800 mg/kg), and cadmium (Cd > 12 mg/kg) near the haul road. Concentrations decreased rapidly with distance from the road, but remained elevated at transect endpoints 1000 m – 1600 m from the road (Pb >30 mg/kg, Zn >165 mg/kg, Cd >0.6 mg/kg). Samples collected on the downwind (north) side of the road had generally higher concentrations of heavy metals than those collected on the upwind (south) side.
Enrichment factor (EF) analysis of moss versus soil parent material demonstrates that remobilized soil (e.g., dust composed of roadbed material) account for only a fraction of the elevated heavy metal concentrations on the road corridor. Enrichment in Pb, Zn, and Cd from airborne sources other than remobilized soil (e.g., ore concentrate) is readily apparent. Analysis of dust shaken from vegetation adjacent to the haul road shows low to average levels of crustal elements (aluminum and iron) and extremely high levels of heavy metals. This is especially striking in comparison to materials site samples that differ in being very low in heavy metals. Considered together, these results suggest that ore concentrate escapement is occurring along the haul road corridor. The fact that EF levels remain elevated even at transect endpoints suggests the additional possibility of contributions of airborne heavy metals from mining activities to the Omikviorok River drainage as a whole. The source of these larger scale contributions is unknown and may include the haul road, port site, mine site, and/or a currently unidentified source.
Results from this study showed Pb levels in excess of 60 mg/kg dw in all transect points ¡Ü 100 m, with a longer shadow on the downwind (north) side of the road. In the Nordic moss monitoring program, H. splendens samples in excess of 60-80 mg/kg dw Pb are considered characteristic of highly polluted areas. Lowest heavy metal concentrations were seen in moss samples 1000 m – 1600 m from the road on the upwind (south) side. However, even these samples greatly exceeded maxima seen in previous H. splendens from arctic Alaska and contained 4-7 times as much Pb, Zn, and Cd as heavily dustladen samples taken adjacent to the Dalton Highway (Prudhoe Bay Haul Road) in northcentral Alaska. Highest levels near the Red Dog Haul Road equal or exceed (1.5 – 2.5 times) maxima reported for samples from severely polluted regions in Central European countries.