Temporal trends of semivolatile organic contaminants in Great Lakes precipitation

Precipitation was sampled around the Great Lakes as part of the Integrated Atmospheric Deposition Network (IADN) from 1991 to 1997. Many of the monthl y volume weighted mean concentrations of the analytes have significantly de creased during the last 6 years with first-order half-lives on the order of 3 +/- 2 years. There was little, if any, spatial variability in the observ ed half-lives, suggesting similar loss processes for the various lakes and suggesting that the decrease in precipitation concentrations reflects a reg ional decrease in environmental levels. The first-order half-lives of organ ochlorine pesticide concentrations in Great Lakes precipitation were not si gnificantly different than the corresponding atmospheric gasphase, lake wat er, and biota half-lives, suggesting that the entire system is at or near l ong-term equilibrium.