What is Mercury?
Mercury is a naturally occurring chemical element found in rock in the earth’s crust, including in deposits of coal. On the periodic table, it has the symbol “Hg” and its atomic number is 80. It is released into the environment from volcanic activity, weathering of rocks and as a result of human activity.
Elemental mercury is a shiny, silver-white metal, historically referred to as quicksilver, and is liquid at room temperature. It is used in older thermometers, fluorescent light bulbs and some electrical switches. At room temperature, exposed elemental mercury can evaporate to become an invisible, odorless toxic vapor. If heated, it is a colorless, odorless gas.
Mercury emitted into the air eventually settles into water or onto land where it can be washed into water. Once deposited, certain microorganisms can change it into methylmercury, a highly toxic form that builds up in fish, shellfish and animals that eat fish. Most human exposure to mercury is from eating fish and shellfish contaminated with methylmercury worldwide.
Human activity is the main cause of mercury vapour releases, particularly coal-fired power stations, residential coal burning for heating and cooking, industrial processes, waste incinerators and as a result of mining for mercury, gold and other metals.
Health Effects from Mercury Exposure
Toxic effects include damage to the brain, kidneys and lungs. Mercury poisoning can result in several diseases, including acrodynia (pink disease), Hunter-Russell syndrome, and Minamata disease.
Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination.
Acute exposure to mercury vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. Occupational exposure has resulted in broad-ranging functional disturbance, including erethism, irritability, excitability, excessive shyness, and insomnia. With continuing exposure, a fine tremor develops and may escalate to violent muscular spasms. Tremor initially involves the hands and later spreads to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, loss of memory, vivid dreams and depression.
Mercury Elemental Vapour Exposure Limits
STEL: 0.03 mg/m3
TWA: 0.01 mg/m3
IDLH: 10 mg/m3
PEL: 0.1 mg/m3
TWA: 0.025 mg/m3
IDLH: 10 mg/m3
In addition to personnel safety, there are also process safety aspects related to mercury. A phenomenon known as liquid metal embrittlement can occur when some equipment is exposed to liquid elemental mercury and has been the cause of multiple equipment failures within the oil and gas industry. One example took place at the Moomba gas plant in Australia, where a piece of cryogenic aluminium equipment was unknowingly exposed to liquid mercury, leading to a metallurgical failure; a significant rupture occurred which led to a loss of containment resulting in a fire.
Which industrial processes commonly cause Mercury vapour releases?
Mercury released from ongoing human activity can be separated into four broad categories. The first category is “area sources”. Landfills, dental preparations, and laboratory use are defined as area sources. The second category is combustion processes. These include coal-fired power generation, medical waste incinerators, and municipal waste combustors. The third category is the manufacture of metals, alkali, and cement. Other industrial processes fall into the fourth category.
- Artisanal Small-Scale (and often illegal) Gold Mining
- One of the largest mercury emitting market sectors exposes miners to toxic mercury vapor when they use the chemical to extract gold from ore. The Guyana Shield region (Surinam, Guiana and French Guiana), Indonesia, The Philippines and part of Western Africa’s coast (e.g., Ghana) are particularly impacted
- Power Plants
- Burning of fossil fuels (primarily coal) for energy, the mercury becomes airborne and is vented to the atmosphere.
- Non-Ferrous Metal Production
- Mercury emissions produced from the mining, smelting and production of metals (not including gold and mercury itself) depends on the levels of mercury in the ore, the techniques used in smelting and the use of pollution controlling devices.
- Steel Production
- Burning iron ore, coke and limestone in electric arc furnaces used to produce steel
- Upstream Oil and Gas Production
- Some regions can produce relatively high amounts of mercury in oil and gas wells, additionally as wells age, mercury content can increase.
- Residential / Industrial Fires
- Burning consumer products that contain mercury, like electronic devices, batteries, light bulbs and thermometers, that are thrown into garbage that is incinerated
- Mercury is still found in many industries, including in battery, thermometer, and barometer manufacturing.
- Biomass Burning
- Biomass burning is the combustion of organic matter. Burning can be from natural or manmade fires.
- Cement Production
- Mercury is present in the raw materials (e.g., limestone) and/or in the fuel (e.g. coal) used in the cement manufacturing process.
- Chlor-Alkali Plants
- Chlorine Production
- Mercury is used in many fungicides