Do you remember playing with mercury from a broken thermometer as a child – rubbing it on pennies and your skin? The element Mercury, or “quicksilver”, is a dense, grey, lustrous liquid metal at room temperature. Mercury also exists as organic and inorganic chemical compounds. It is a natural occurring element found in geologic seams of its main ore, a red sulfide mineral called Cinnabar. Elemental mercury is also found in the atmosphere and may come from man-made sources (coal-fired power plants and industrial processes) or natural sources (volcanoes, forest fires and ocean emissions).
Mercury may also form organic compounds – the most common of which is methyl-mercury, a toxic chemical that results from a reaction of carbon with elemental mercury through a microbiological process. Methyl-mercury is found in waters across the globe and is known to bioaccumulate in the aquatic food chain.
Mercury forms inorganic compounds – such as thimerosal, that is used as a preservative in vaccines – during reactions with nitrogen, sulfur, oxygen and other elements. Because inorganic mercury is relatively less toxic than other forms, elemental mercury is chemically reacted with an applied reagent during environmental cleanups to form a less harmful mercury salt compound, which is then recovered.
Usage and Legacy
Due to its special physical and chemical properties, mercury became an important industrial and commercial metal. Some of the uses of mercury have been in gold-mining, thermometers, barometers, pressure gauges, dental amalgams, an ancient pigment called vermillion, caustic soda production, catalysts in rubber flooring, and an explosive called mercury fulminate.
Facilities or properties that may have mercury include, but are not limited to, dental offices, chemistry labs, warehouses with large quantities of fluorescent and mercury vapor lamps, and any industrial processes that use mercury-containing inputs or by-products.
Due to its toxicity, most industrial and commercial uses of mercury have been discontinued or greatly reduced. However, it is still commonly encountered in homes, workplaces and schools. For example, mercury off-gases from flexible flooring used in school gymnasiums. And properties with historic industrial usage may be contaminated with mercury, especially if the activities pre-date the existing mercury regulations implemented over the last 40 years.
Exposure and Toxicity
The current primary sources for human exposure to mercury are dental amalgams, fish consumption, air pollution from fossil fuel power plants, and occupational contact.
The most common pathway for elemental mercury entry into the human body is by inhalation, although dermal absorption and ingestion may also occur. Severe, acute exposures cause corrosive bronchitis and pneumonitis with symptoms of potentially fatal central nervous system (CNS) effects. Chronic exposures primarily produce non-specific signs and symptoms of CNS damage – including tremors; loss of muscle control, ranging from spasms to paralysis; loss of vision or visual disturbance; loss of memory; damage to hearing and speech; etc. – with the most serious cases resulting in coma and death. Elemental mercury also damages the kidneys, where it accumulates.
The Mad Hatter, a character from Lewis Carroll’s “Alice’s Adventures in Wonderland”, was named after hat makers in England, Many workers suffered dementia and tremors following occupational exposures to mercury nitrate in felt production for the fur and hat industry. And, in Danbury, Connecticut, the “Hat Capital of the World” during the 19th and early 20th centuries, mercury-induced tremors among hat workers were so common, they became known as “The Danbury Shakes”.
Inorganic mercury exposures are primarily caused by ingestion and have an irritating effect on the gastrointestinal system – capable of causing severe abdominal cramps, corrosive ulcerations and bleeding, as well as damage to the kidneys similar to elemental mercury. It appears that kidney damage may be reversible, however, if the exposure to inorganic mercury is removed.
Methyl-mercury accounts for the largest portion of environmental mercury exposure to humans. Health effects from exposure to this organic mercury compound are CNS toxicity and damage to the fetus in pregnant women. The primary target organ is the brain and the CNS effects are similar to other forms of mercury. Fetal damage is caused during development of the brain and results in psychomotor effects that may appear similar to cerebral palsy. The majority of neurotoxic damage is irreversible in adults and children. Most of the clinical knowledge of methyl-mercury poisoning has been compiled from studies of 20th century epidemics caused by contaminated seafood in Japan and from contaminated grain imported from the U.S. and Mexico to Iraq that was not intended for human consumption.
Perhaps the worst example of wide-scale mercury poisoning occurred in Minamata, Japan between 1932 and 1968. The local chemical factory, operated by the Chisso Corporation, discharged methyl-mercury laden wastewater into Minamata Bay and tributaries. As discussed earlier, methyl-mercury is very persistent in the environment, allowing it to bioaccumulate in the fatty tissue of fish which then passes through the aquatic food chain. The local population relied upon the fish and shellfish from Minamata Bay as a dietary staple – resulting in thousands of cases of severe and sometimes fatal mercury poisoning. The government of Japan determined 2,265 people to be permanently disabled by “Minamata Disease”, a neurological syndrome primarily of the central nervous system. The Chisso Corporation was held responsible for compensation to affected individuals, many of whom are still alive, as well as for environmental remediation – currently totaling approximately 175 billion yen (about $1.6 billion US) according to the Japanese Ministry of the Environment.
Currently, in the United States there are several lawsuits dealing with human exposure and environmental pollution from the use and improper disposal of mercury-containing dental amalgams.
EHS Regulations in the United States
Mercury and mercury compounds are highly regulated substances in the U.S. – with enforcement responsibilities across many agencies. Their sale and use in commerce has been both regulated and driven by consumer and environmental concerns. The United States Department of Transportation (USDOT), the Environmental Protection Agency (USEPA), and the Occupational Safety and Health Administration (OSHA) have passed regulations that must be addressed when mercury is present in industrial processes, waste recycling and disposal.
Mercury and many mercury compounds are classified as hazardous under the USDOT Hazardous Materials Transport Act and must be managed, transported and shipped as hazardous material. OSHA considers mercury a hazardous substance and requires hazard communication, training, and personal protective equipment (PPE) compliance. OSHA has established a Permissible Exposure Limit of 0.1 milligrams per cubic meter (mg/m3) for elemental and inorganic mercury and 0.01 mg/m3 for organic alkyl mercury compounds. These are both “ceiling” limits, which means they cannot be exceeded for periods longer than fifteen minutes.
The USEPA monitors emissions of mercury into the atmosphere through the Clean Air Act. Mercury is designated as an EPA Hazardous Air Pollutant and point sources are subject to performance standards under National Emissions Standards for Hazardous Air Pollutants. The regulatory framework to reduce mercury air pollution from the largest domestic source, coal-fired electrical generation, is still being debated. There are no ambient air quality standards for mercury in the U.S.
The USEPA Clean Water Act regulates mercury emissions from point sources through the National Permit Discharge Elimination System (NPDES) and individual states set environmental water quality standards. Mercury and mercury-containing wastes are classified as hazardous waste under the EPA Resource Conservation and Recovery Act (RCRA). Facilities storing quantities of mercury above a threshold limit must follow reporting requirements for emergency preparedness. States may also have EHS regulations that are more stringent than their federal counterparts.
Mercury Compliance Services…from HETI
HETI’s Certified Industrial Hygienists and environmental professionals are available to assist clients comply with the array of mercury regulations. Whether the need is for written programs, training, workplace exposure assessments, or simply addressing questions on compliance, we are here to help.