SEASONAL CONTROLS ON THE FORMATION AND TRANSPORT OF METAL NANOPARTICLES IN A MINING-IMPACTED RIVERINE ENVIRONMENT

The formation and transport of geogenic and biogenic metal nanoparticles from the flux of hydrologic and biogeochemical systems in mining-impacted environments is a developing concern because of the potential for greater distribution and bioavailability of such particles. The mining-impacted lateral lake and wetland complex of the Coeur d’Alene River in northern Idaho is producing transportable nanoscale metal particles during the summer dehydration low of the riverine system and contributing to the metal contamination of the downstream Lake Coeur d’Alene. Analysis of dissolved and total phase metals in the Coeur d’Alene River indicate primarily dissolved phase metals being transported through the lower Coeur d’Alene River to Lake Coeur d’Alene during the groundwater-dominant summer dehydration period. The dissolved metals are not associated with suspended sediments as indicated by the lack of correlation of suspended sediments and dissolved metal concentrations. An examination of sediments from a lateral lake indicate the production of metal nanoparticles around weathering metal sulfides that likely are flushed to the surface water system during the summer dehydration and change in hydraulic gradient. Such transport is further indicated by metal deposits along lake margins and riverbanks where metal precipitation occurs with the decline in water level and disconnect of those pathways to surface water systems.