Dirt from Abandoned Mines May Cause Cancer

The Nevada County landscape is scarred by gold mining: the piles of tailings in Empire Mine State Park, the exposed bluffs framing Hirshman’s Pond. But the toxins left over from mining are invisible. You may have wondered: Is living next to all these old mines bad for my health? 

The answer may be yes. Scientists from the University of California and UCSF working in collaboration with the Nevada City-based environmental group Sierra Streams Institute (SSI), have found evidence that exposure to arsenic and cadmium in local soils and well water may lead to a higher risk of breast cancer. 

The data comes from a seven-year research project, now concluding its third study. Called the Community Health Impacts of Mining Exposure, or CHIME, the project was designed to explore why, according to official health indexes, Nevada County has some of the highest rates of breast cancer in the state. 

“Breast cancer rates tend to be higher in urban rather than rural areas, so when we saw that, we were puzzled,” says UCSF epidemiologist and CHIME researcher Peggy Reynolds. “That provoked a little, ‘Hmm, what could be going on there?’”

In the first pilot study, CHIME researchers collected and analyzed urine samples from approximately 60 women. They ranged in age from their 20s to their 70s, and had been living in Nevada County anywhere from a few years to several decades. The women also answered a questionnaire that probed their smoking history, diet, where they had lived in the past, and what types of outdoor activities they engaged in. There were questions specifically about trail running, hiking, and gardening, because those are activities that put you in close proximity to dirt. It also asked about their current residence, such as: Do you live on a dirt road? Are you on a well?

Image of Hirshman’s Pond via Yelp.com, with bluffs exposed from hydraulic mining visible at right.

Researchers found that the Nevada County participants had higher “body burdens” of arsenic compared to the national average. Women who had been living in the county for longer had higher levels of cadmium. Women who grew and ate their own vegetables had higher arsenic levels than those who did not, though this difference was not deemed statistically significant by the researchers.

The results were peer reviewed and published in 2019 in the  International Journal of Environmental Research and Public Health. But that was just the beginning.

“It raised the question of why?” says Taylor Schobel, SSI’s rural health coordinator.

When people think about toxins from mining, they usually think about mercury, which was historically used in hydraulic mining to bind to the gold dislodged from the hills. Mercury residue in reservoirs and streams in Nevada County is a real concern, particularly as it relates to build-up in fish that people consume. But other heavy metals that accumulated from the mining process, and their effects on human health, are only just beginning to be understood. 

Arsenic and cadmium, the two metals that researchers in CHIME focused on, were not chemicals added to the environment by old timey miners. Rather, they are naturally occurring metals in the ground. After miners brought up rock from beneath the surface and extracted the gold, they dumped the waste rock and processed ore (called tailings) on the ground, wherever convenient; they left tailings in big piles on pieces of unused land, sometimes in ponds. The displacement of organic soil that would have diluted these carcinogenic metals left more arsenic and cadmium in the rock dust and exposed ground than would naturally occur. 

The Agency for Toxic Substances Management Committee (ATSMC) has identified cadmium as the world’s sixth most harmful substance that destroys human health. Evidence from previous scientific studies has suggested that heavy metals like arsenic and cadmium may act as endocrine disruptors, putting women with increased exposure to them at a higher risk of breast cancer. 

With their preliminary findings, the CHIME team secured additional grants and began a second pilot study. In CHIME 2, launched a few years later, the team studied the same number of women, but this time the sample included women with a history of breast cancer. The first study had not targeted women with breast cancer.

“We wanted to look at: Is there a difference between women who had had breast cancer and not?” says Schobel.

Rather than urine sampling, researchers visited participants and took soil and dust samples from their houses and yards. In the case of women with wells, the team also took water samples.

The question was: Where are women getting exposure to these metals? Is it on their own properties?

The team did not find any cadmium in their household sampling. But they did see somewhat higher levels of arsenic in some of the samples, and notably higher levels in the soil of women who had had breast cancer. The findings were enough to encourage the CHIME team to keep researching.

In the third and most recent CHIME study — projected to wrap up later this summer — the sample size remained the same. This time, participants were recruited from a wider area, including most of the other Gold Country counties, and Yuba County. This third study also included a mapping component, where the team began looking at incidents of breast cancer in Gold Country in proximity to abandoned gold mines. The results of this study are tentatively set to be released to the public in early fall at the Sierra College Science Lectures series. 

So how concerned should we be about the results of this research? The team behind it had a measured response.

“Breast cancer is a disease that has a very long latency,” says Peggy Reynolds, the epidemiologist from UCSF. She says that we should take into account that these studies were not longitudinal, which makes them far from conclusive. 

“We think there are windows of susceptibility that might be very important — exposures in utero, adolescence, later in life at certain times,” says Reynolds. “And it’s very difficult to follow someone for their lifetime and see what happens.” 

So, in other words, someone with breast cancer might have gotten it from being exposed to Nevada County toxins, or might have been exposed to cancer-causing toxins in the past somewhere else.

And then there’s the issue of the small sample size. Ideally, a series of smaller studies like these will lead to continued studies involving 1000s of participants over a longer time period, which would provide more statistically significant results. 

Nonetheless, the CHIME researchers insisted that the value and potential importance of studies like theirs shouldn’t be underestimated. Kyle Leach, a geologist for SSI, points out that studies like the CHIME studies that were done on fish and mercury eventually led to now commonplace fishing advisories. Without them, we wouldn’t have messaging like the signs at Hirschman’s Pond that tell you to only eat small amounts of fish because of mercury buildup.

“But this is a new area,” says Leach. “Regulatory limits themselves are based on guidelines, which are based on what we think the exposure would be based on risk.” The CHIME studies pave the way for deeper research which could lead to official health recommendations like the fishing advisories.

When asked whether they, themselves, were worried about the risks of heavy metals, the researchers said that they take precautions. Katy Janes, an engineering geologist involved in CHIME 2, says she towels off her pets before letting them in the house, and always takes off her shoes indoors, to avoid tracking in excess dirt. Schobel uses only store-bought dirt for her garden. She lives in an area of Nevada City where she can see visible piles of mine tailings and capped off mine shafts throughout the surrounding woods. 

Nevada City mine tailings turned into a bike jump.

On a stroll down a trail across the street from her house, we saw an area where local mountain bikers had turned a pile of mine tailings into a bike jump. “Would you mountain bike here and inhale all of that dust?” mused Schobel. “I probably wouldn’t.”

Lead image of Taylor Schobel is by Lessley Anderson.

More to explore

Leave a Comment