“In recent years, increased attention has been paid to the role that toxics may play in the problems facing Chesapeake Bay. Through a recent reevaluation of a 1989 basinwide toxic reduction strategy, the Bay Program has determined that toxics problems exist in some locations in the Bay. A few well-known areas have serious, localized problems, and some other regions that were previously thought to be uncontaminated have shown toxic effects. No evidence was found of severe, system-wide responses to toxics similar in magnitude to the effects observed throughout the Bay due to excessive nutrients. Widespread areas have measurable levels of toxic substances, below thresholds associated with adverse effects on the Bay’s living resources. The long-term effects from these low levels remain unclear. Through efforts to develop a basinwide toxics loading and release inventory, estimates of direct atmospheric deposition to tidal surface waters have been made using data from a sampling network set up in 1990. Atmospheric deposition was found to be a significant source of metals, organics, and pesticides loadings to the Bay’s tidal waters, although not the major source. Recent research and assessments of sediment contaminant patterns in Chesapeake Bay indicate that atmospheric deposition may be the major source of sediment contamination, particularly of polynuclear aromatic hydrocarbons resulting from incomplete combustion of fossil fuels.”