Sources and Toxicity of Mercury in the San Francisco Bay Area, Spanning California and Beyond

Abstract

This report synthesizes and evaluates published scientific literature on the environmental occurrence and biomagnification of mercury with emphasis on the San Francisco Bay Area (SFBA), California. Mercury forms various compounds, well known for their toxicity in humans and environmental ecosystems. Elemental mercury is transported and distributed by air, water, and sediments. Through the metabolic processes of algae and bacteria, mercury is converted into organic compounds, such as methylmercury (MeHg), which then bioaccumulates up through trophic levels. In fish, it is found primarily in skeletal muscle, while in humans, the primary target organs are the brain and kidneys. Health concerns exist regarding bioaccumulation of mercury in humans. This paper reviews the known anthropogenic sources of mercury contamination, including atmospheric deposition through aerial transport from coal burning power plants, cement production, and residual contaminants of mercury from gold mining, as well as mercury-containing waste from silver amalgams emitted from dental offices into waterways. Although tools exist for measuring mercury levels in hair, breast milk, urine, blood, and feces in humans, current diagnostic tools are inadequate in measuring total mercury load, including deposited mercury in tissues. Additionally, insufficient attention is being paid to potential synergistic impacts of mercury interaction with multipliers such as lead, cadmium, and aluminum. We provide specific data on methylmercury concentrations at different trophic levels, followed by recommendations for reducing the level of mercury in the SFBA in order to protect the health of humans and other species.

Figure 1

Global distribution of anthropogenic mercury emissions to air in 2010. Figure source: United Nations Environment Program [26].

Figure 2

Anthropogenic global mercury emissions, tons, 1995–2005. Figure source: United Nations Environment Program [26].

Figure 3

Data for 2010 mercury emissions from the highest emitting industry sectors, from the 2013 UNEP Global Mercury Assessment. Figure source: United Nations Environment Program [26].

Figure 4

Map of mercury mines in California. Figure source: United States Geological Survey [35].

Figure 5

Map of gold mines and mercury waterways in California.

Figure 6

Mercury biomagnification in an aquatic and riparian food chain. Source: New Jersey Department of Environmental Protection, Mercury Task Force [44].

Figure 7

California least tern in trophic level III is a small endangered seabird exhibiting pathologies related to MeHg contamination. It typically inhabits lagoons or shallow estuaries, where it feeds on the abundant small fish. Photo source: California Dept. of Pesticide Regulation (cdpr.ca.gov). Photo by Moose Peterson of Wildlife Photography, http://www.moosepeterson.com.

Figure 8

A team of scientists and citizens (young students in this case) in 2015 collecting dragonfly larvae at Golden Gate National Recreation Area in San Francisco. Photo source: United States Geological Survey [4].

Figure 9

SFBA native bird species in trophic level IV are at varying risks from mercury toxicity. This figure shows relationship between MeHg levels and diet. Those at higher trophic levels, e.g., Forster's tern, have a greater risk due to their consumption of more highly contaminated mercury-tainted organisms. Figure source: Ackerman et al. [57].