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Toxic trails, to you….


The magnificent scenery, the blue skies, the wind in your face as you hike, mountain bike, or ride your horse, dirt bike or off-highway vehicle (OHV) through California’s Gold Country….

What could feel more natural?

Well, lead, arsenic, and asbestos are natural, too! :-)

The Sierra Fund released a study on June 22, 2010, “Gold Country Recreational Trails and Abandoned Mines Assessment” (PDF), which was subtitled, “A Pilot Study to Assess Exposure Potential to Toxins from Mine Waste and Naturally Occurring Hazardous Substances.”

After all, the Gold Rush had many other effects besides bringing a lot of people to California!

In the introductory section of the study, there is a bit about (and contact information for) The Sierra Fund, as well as this description of the released study, and of another study to be released this month.

“In 2009, The Sierra Fund initiated two pilot studies to learn whether people who live, work, or recreate in the Sierra Nevada are being exposed to legacy mining toxins including mercury, arsenic, lead, asbestos and chromium. Results of the study of Gold Country Recreational Trails and Abandoned Mines Assessment are presented here. The 2009 Gold Country Angler Mercury Exposure Survey, which looks at exposure to mercury from eating fish caught in Sierra lakes and rivers, will be released in July 2010.”

The study reports the methods used (as the result of my scientific education, this is always where I start reading), as well as information on the toxicity of lead, arsenic, asbestos, silica (1), and mercury. The study also discusses physical hazards, as well as chemical hazards.

(Before I go any further, I should mention that it does not take human activity like mining to bring hazardous materials to places where they come in contact with people. This Bureau of Land Management (BLM) Web page describes naturally occurring chrysotile asbestos in the Clear Creek Management Area near Hollister, where human exposure occurs during camping, hunting, and the riding of motorcycles and dirt bikes, especially during the dry season when significant dust is raised. The natural occurrence of large amounts of toxic materials in California tends to be ignored by members of the California Legislature who use “toxicity” as an argument against very small quantities of lead shot in AEROBIC environments [AB 2223]. The real “target” of such legislation is “hunting” and stems from a fundamental lack of understanding of predation in nature and the roles it plays in maintaining healthy natural systems. As an aside,  all three pieces of the foolish, “goofy” legislation [perhaps one piece is NOW clearly unconstitutional] mentioned in that blog entry [about the generic, endangered California Legislative “maroon“] have PASSED the California General Assembly and are awaiting action in the Senate.)

The Sierra Fund report contains a wealth of information, including tables and topographic maps of study sites. According to Dr. Carrie Monohan, The Sierra Fund’s Science Director and principal author of the report, “The purpose of this study was to learn whether people are potentially being exposed to dangerously high levels of heavy metals while engaging in dusty recreation activities in and around abandoned mines. Our results show that this is in fact the case in some areas, and more assessment is urgently needed.”

A summary of the results from the study is presented verbatim (links added) below:

At certain locations, toxins were found at levels that could affect human health:

  • In the Nevada City area, arsenic was found at levels of concern on Banner Mountain trails, and asbestos in one location on the Newtown Ditch trail used for biking and hiking.
  • At the Foresthill OHV Area in and around the abandoned Marrall Chrome Mine pit, samples showed up to 40% asbestos and off-the-charts levels of lead in the soil on trails where families ride OHVs.
  • In the Downieville area, certain biking, hiking and OHV trail locations tested high for arsenic, lead and asbestos.

There is also good news: the study found that several popular areas including the “Downieville Downhill” mountain bike trails, the Eureka Diggings OHV Area, and the Western States Trail near Foresthill, while they pass several abandoned mines, do not pose a health threat to recreationists.

Key recommendations of the study include:

A dust exposure study that looks at exposure scenarios of different recreational activities, and

  • Clear, visible advisories in areas that are known to be contaminated by substances that are dangerous to human health,
  • Additional sampling of contaminated areas,
  • In the Downieville area, certain biking, hiking and OHV trail locations tested high for arsenic, lead and asbestos,
  • A survey of people recreating in these areas to learn more about their exposure, and effective outreach and education methods.

The full report and executive summary can be downloaded from The Sierra Fund’s Mining Initiative Resources page.

As with most things in California, natural hazards are, somehow, controversial! :-) There are dirt bikers and other off-roaders who seemingly do not believe that asbestos and other toxic substances are BAD for them. I could introduce them to a friend of mine from high-tech days whose father was terminal with asbestosis from his work as a miner in Libby, Montana and is probably dead by now. Thousands in the city of Libby, Montana, as well as vacationers from other places, were affected by asbestosis, lung disease, and mesothelioma. But people who have their minds made up are not usually susceptible to facts, whether on dirt bikes or in the California Legislature….

-Bill at

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