Figure 6.

Lead isotopic compositions of San Francisco Bay waters and potential lead sources. Bay waters are shown as fields that encompass the waters collected during low flow (brown outline) and high flow (blue outline). A third field (black outline) surrounds all San Francisco Bay waters collected in 1989 and waters in the South Bay throughout the study period. Possible sources of lead to the bay include 1960s–1970s leaded gasoline (dark red), 1980s leaded gasoline (light red) (2, 34–44), preindustrial bay sediment as recorded in the bottoms of sediment cores (19), and a component representing hydraulic mine sediments (24).