Atmospheric transport and fate of herbicides at pristine Isle Roylae National Park, Lake Superior

Cromwell, Aron; Thurman, E

Herbicides used in agricultural areas are being transported atmospherically and deposited by precipitation onto pristine watersheds, such as Isle Royale National Park (an island park located in Lake Superior). Samples of rainfall, surface water, and soil water were collected during the summers of 1992, 1993, and 1994 and were analyzed by combining solid-phase extraction with either GC/MS or immunoassay. Atrazine, cyanazine, and two of atrazine's metabolites, desethylatrazine (DEA) and desisopropylatrazine were detected in Isle Royale rainfall from mid-May to early July at concentrations of less than 5 nglL to over 2000 ng/L. Air parcel back trajectories indicate that most of the herbicides deposited on Isle Royale originate in the corn belt. The annual mass of herbicides deposited varied between years, with 1994 having the greatest mass deposited (5.8 /ug/m^2). Furthermore, atrazine and DEA were found in concentrations of less than 5 ng/L to 30 ng/L in eleven lakes across Isle Royale. It is hypothesized that the degradation rate of atrazine is more rapid in shallow lakes and soilwaters and slower in deep lakes of Isle Royale. Degradation of atrazine in lakes of Isle Royale is estimated to be on the order of years for the deeper lakes, which is indicated by an increase in the DEA to atrazine ratio over time.