Community Health Impacts of Mining Exposure

In this community-based research project, funded by the California Breast Cancer Research Program, we are partnering with Cancer Prevention Institute of California epidemiologist Dr. Peggy Rull to begin to answer the question, "What impact does historic gold mining have on human health today?"

With the help of sixty women from the local area, we are measuring the amount of cadmium, arsenic, and other metals found in the bodies of the women who live here. This pilot study will examine whether there are residential and lifestyle factors in a mining-impacted community that are associated with increased levels of these metals in women's bodies.

The women are divided into two age groups--18 to 35 and over 35--and then divided again according to length of residency in Gold Country. Each participant provides a sample of urine and toenails, and completes a questionnaire of basic demographic information, diet and regular activities, as well as a full residential history.

Cadmium and arsenic were chosen because they are pervasive throughout Gold Country, and because they are carcinogens and "metalloestrogens" that are considered provocative with respect to breast cancer etiology. The counties that make up Gold Country have consistently higher age-adjusted rates of breast cancer than the rest of the state. In fact, the three most populous counties in Gold Country (Nevada, Placer and El Dorado) have incidence rates in the top 10 of California counties, while the combined incidence in Mariposa and Tuolumne Counties is the second highest in the state. This runs counter to the trend of lower breast cancer rates in more rural areas. After many years of working with the community to collect environmental monitoring data, we are pleased to begin the next step, which is connecting the dots between the health of the environment and that of the humans who live here.

Sierra Streams scientists hypothesize that mercury is transported downstream over dams in the form of either methyl mercury absorbed by algae or fine particles of highly methylation-prone elemental mercury that are trapped in an algae-sediment mixture. The mercury-containing algae or algae-sediment mixture is thought to be mobilized during storm events, during the annual dewatering of reservoirs, and during the routine overflow of dams.

Using Lake Wildwood as a study site, Sierra Streams scientists are testing this hypothesis. Data were collected in monthly reservoir sampling, and in periodic sampling efforts below Lake Wildwood during two storm seasons and one dewatering event. Further sampling will be conducted during the reservoir drawdown planned for fall 2011.

Further study is planned, including sampling in additional dammed streams and further analysis of the algae/sediment mixture to determine the transport mechanism for mercury. With the recent large expansion of flow data-gathering capacity in the lower watershed, Sierra Streams scientists will be able to combine storm sampling and flow data to quantify the mercury being transported downstream. During the summer of 2011 we will collect biological specimens upstream, within and downstream of Lake Wildwood to analyze for mercury content. Specimens will include fish, algae, plants, and macroinvertebrates.

storm sampling

Sampling high-water flows below the dam during a March 2010 storm event.

The findings of this study are likely to have widespread application for management of dams throughout the Sierra. We know already that the mercury concentration of algae/sediment in water from the bottom of the Lake Wildwood reservoir is far higher than water from the surface. This suggests that the periodic dewatering, during which water is released from the bottom of the reservoir, allows significant transport of mercury downstream. Changes in management of this process may help to minimize the transport problem.