Three case studies at the regional and global scales of the cycling and fate of lead and mercury in the environment

The study of trace metals in the environment has evolved greatly over the last 30 years as a result of the development of accurate sampling and analytical techniques. This research has resulted in the identification of anthropogenic sources of metals in remote areas, and indicates that human activities have had a profound, widespread effect on the environment. While many metals have toxic effects on both humans and ecosystems, two metals have received a large amount of scientific attention. One of these metals, lead, has been a demonstrated to have neurologic effects on children, and, as a result, initial efforts to regulate human emissions of metals focused on lead. These efforts resulted in the global phase-out of leaded gasoline, the major source of lead to the environment. More recently, scientific attention has been focused on mercury, which, like lead, has been enriched in the environment as a result of industrial activity, and is also a neurotoxin.; The three chapters which compose this thesis aim to contribute to the scientific understanding of lead and mercury in the environment. Chapter 1 addresses information gaps in the estimates of global emissions of mercury, calculating the possible contribution of crude oil processing to the global mercury cycle. The results of this study indicate that the potential emissions of mercury from petroleum refining are large, roughly equivalent to emission estimates from coal combustion and oil refining. Chapter 2 investigates the long distance transport and fate of industrial mercury emissions, and specifically investigates the link between Asian industrial emissions and mercury deposition on the West Coast of North America. The results of this study link Asian industrial emissions and elevated mercury concentrations in rainwater sampled in North America, demonstrating the long-range impact of human activities on mercury deposition. Chapter 3 focuses on the fate of lead in a large riparian system, the San Francisco Bay estuary. This study utilizes isotopic signatures to fingerprint lead sources to San Francisco Bay surface waters, and demonstrates the persistence of past lead emissions (primarily from the combustion of leaded gasoline) in this estuary.