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WORKING WITH MERCURY
Safety article by Harold Hough Feb/March 2009

When many of us were kids, mercury was seen as a curiosity and a toy. A broken mercury thermometer was an event that allowed us to play with the liquid metal by rolling it around in our palms. We were unaware of the long-term threats it posed to us.

Today a major safety and health program for the Mining Safety and Health Administration (MSHA) is making miners aware of the threat of mercury and other heavy metals. Unfortunately, hazards caused by heavy metals are often underestimated because they don’t cause immediate problems, but lead to long term health problems and even cancer. Fortunately, MSHA has several documents available that can help mines reduce the risk from mercury and other heavy metals.

Most mines don’t realize that mercury isn’t just a threat to workers in the mine. Mercury, for example, is released into the air as a vapor from tailings, effecting above ground workers and even administrative personnel.

Mercury and mining have been intertwined for centuries. Not only was it used to refine gold and silver, it’s often found in ore deposits and old tailings. During the Comstock Lode mining era from 1860 to 1895, 15 million pounds of mercury were lost in the Carson River. In cases of massive mercury poisoning, the subject can become irrational, which gave us the expression, “mad as a hatter,” because hat makers used mercury.

Exposure to metallic mercury or mercury compounds, even in small quantities over a period of time, can cause severe poisoning. Mercury can enter the body by inhalation of vapors or mercury-containing dust, by swallowing (ingestion) or by absorption through the skin. Symptoms of chronic mercury poisoning are weakness, fatigue, inflammation and ulcers in the mouth, bleeding gums, loosened teeth, excessive salivation (spittle), tremors (shaking) and emotional instability. Acute poisoning causes nausea, abdominal pain, vomiting, headaches, diarrhea and, (occasionally) cardiac weakness.

MSHA has some recommendations for mines with a potential mercury threat. Miners who are exposed to mercury should take rigorous precautions to prevent poisoning themselves and their families. Work clothes should be vacuumed before removal. Vacuum cleaners used for this purpose must be equipped with mercury-vapor absorbing filters. Every miner should shower thoroughly (with special attention to the head and hands), and change into clean clothing before leaving the job site. Soiled clothing should be stored in vapor-proof containers and must be laundered after each use. Smoking should be avoided completely in mercury work areas. The hands and face should be thoroughly washed with warm soapy water and rinsed before the miner eats or drinks.

Mines that want to learn more about handling mercury threats, can go to the MSHA website and download the document, “Controlling Mercury Hazards in Gold Mining: A Best Practices Toolbox.”

However, mercury isn’t the only heavy metal threat. There is arsenic, which most people associate with Agatha Christie mysteries. However, arsenic is also common in mines and provides both long and short-term problems. Arsenic is usually found in mines as the compound arsenopyrite, realgar, or orpiment. Their risk as a poison is reduced somewhat because they aren’t soluble in water, but they pose a long-term cancer risk, especially lung cancer if inhaled. When they are ingested, they are associated with an increased risk of bladder, kidney, liver, and skin cancer.

Lead is also another threat to miners, in addition to cadmium. Lead found in many gold and silver operations and cadmium is often found in the mining and refining of zinc, and copper. Acute cadmium poisoning usually occurs by inhaling its fumes and may be a source of lung and prostrate cancer.
Unlike some poisons, the body can’t quickly rid itself of cadmium because it bonds with metallothionein, especially in the kidneys and liver. Consequently, it may take ten to thirty years to rid the body of half the cadmium ingested.

Although heavy metals can cause immediate health problems, many of the risks are long term. MSHA has produced a draft toolbox on monitoring miners who are exposed to heavy metals, which is available on its website.

According to experts, the first line of defense is to lower contact with good ventilation. If ventilation isn’t adequate, respirators are recommended. If skin contact is a risk, gloves and adequate clothing should be worn.

One way to monitor the situation is through urine or blood samples. However, these aren’t perfect because some non-toxic arsenic compounds found in seafood can elevate levels. Nor do they detect arsenic found in the lungs. As a result, effective monitoring can’t be limited to occasional testing.

Another way to monitor the site is to install air monitors throughout the site. These devices pump air through a filter where the particulate mater can be monitored. Of course, these monitors are stationary, while workers move around. This means that, as a worker moves through the site, the level of exposure changes. Consequently, personal air monitors clipped to a worker’s clothing are more accurate, although the cost of the monitoring program is much higher.

Although it’s easy to dismiss heavy metal exposure because its results aren’t as dramatic as an accident, mines can’t dismiss them. Even if you follow the MSHA or OSHA standards, recent studies show that they may not be enough. The smart thing to do is to anticipate future government standards (a good possibility with the Obama administration) by aggressively monitoring and avoid heavy metal poisoning.