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 monthly volume weighted mean concentrations of the analytes have significantly decreased during the last 6 years with firstorder half-lives on the order of 3 ± 2 years. There was little, if any, spatial variability in the observed half-lives, suggesting similar loss processes for the various lakes and suggesting that the decrease in precipitation concentrations reflects a regional decrease in environmental levels. The first-order half- lives of organochlorine pesticide concentrations in Great Lakes precipitation were not significantly different than the corresponding atmospheric gasphase, lake water, and biota half-lives, suggesting that the entire system is at or near long-term equilibrium.