Mercury is a naturally occurring metallic element, which at room temperature and in its pure form is a silvery-white liquid. Its melting point is -39°C and boiling point 356°C. It has a uniform volume of expansion over its entire liquid range and low electrical resistivity.
As mercury is a liquid at room temperature and expands when it heats up, it has been widely used in measuring devices such as thermometers and barometers. However, if a measuring device is damaged and the mercury is released, the mercury will evaporate slowly, and nearby people may be exposed. Contamination of clothing and cleaning equipment can also occur when dealing with the spillage and broken instrument.
Owing to these risks, the sale of mercury measuring devices is now restricted. This in turn means a reduction in mercury being released into the environment from landfills and incinerators.
Mercury is also found in a range of other products, including dental amalgam, electrical switches, batteries, fluorescent light tubes, biocides, pesticides, herbicides and fungicides, pigments and dyes, and wood and leather preservatives.
Risk to human health
Mercury is very toxic. High doses can be fatal to humans, but even relatively low doses can have serious impacts on the body’s systems.
The harmful effects of exposure largely depend on both the way people are exposed and the type of mercury they are exposed to. Very little enters the body after swallowing small amounts of elemental mercury, whereas after breathing elemental mercury vapour about 80% enters the blood from the lungs. Inorganic mercury compounds do not vaporise and so are not generally breathed in, and only small amounts may pass through the skin. If swallowed, up to 40% may enter the body.
Breathing in elemental mercury vapour for a short time affects the nervous system and lungs leading to tremors, walking difficulties, chest pains and breathlessness. After longer periods, the lining of the mouth and lungs may be damaged. Kidney damage may also occur as well as stomach irritation, nausea, vomiting and diarrhoea. Eating food or drink contaminated with inorganic mercury damages the kidneys, stomach, intestines and nervous system. Mercury has been linked with possible effects on the cardiovascular, immune and reproductive systems.
Mercury in the environment can change into methyl mercury, the most toxic form of mercury. Methyl mercury can cross the placenta in pregnant women and can affect mental development in unborn babies.
Mercury and divalent inorganic compounds, including mercuric oxide and mercuric chloride (measured as mercury), have a long-term (eight-hour time weighted average) workplace exposure limit of 0.02mg/m3 as given in the Health and Safety Executive’s EH40 document.
Risk to the environment
Mercury is persistent in the environment. It can build up in plants and animals, and accumulate along the food chain, particularly in fish and other aquatic life. Low levels of mercury in surface waters can lead to high concentrations in insects, fish and birds, resulting in very toxic contamination in parts of the ecosystem. Measuring devices from consumers may end up in landfill and, over time, the mercury from measuring devices has the potential to cause environmental problems in leachate (the liquid waste from landfill) and groundwater. Groundwater feeds rivers and is also used for drinking water supplies.
Mercury can be handled safely by laboratory personnel, although its use should be eliminated or minimised wherever possible. Safe handling tips where its use is unavoidable include the following.
- Never use a mercury thermometer in a laboratory oven.
- Do not leave open containers of mercury in the laboratory. If used in a bubbler, the exhaust should go up a vertical tube to eliminate splashing and should be vented to a fume hood.
- Do not keep excess mercury – purchase only amounts that will be completely used.
- Use a glass, plastic or steel tray to contain any spills that might occur.
- Glass or plastic vessels should have a secondary steel or plastic container around them in case the vessel fails.
- Do not use mercury where it could contact a hot surface and vaporize.
- Avoid inhaling mercury vapor and use suitable gloves when working with it.
- Put mercury waste in a special waste container, do not combine it with other wastes and do not dispose of it down a sink.
- Do not wear gold or silver jewelry when working with mercury.
- As always, read the material safety data sheet (MSDS) for mercury before using it.
- Access to mercury should be restricted to a locked cabinet or room, and only used by those have been given suitable and sufficient training.
With proper control and training, elemental mercury can be safely used in a laboratory setting. However, when spilled or misused, it can present a significant hazard.
The British Occupational Hygiene Society (BOHS) advises the following actions to be taken in case of a mercury spillage.
- Make an on-the-spot assessment of the severity of the spill. Seek assistance whenever necessary.
- Wear gloves. Collect as much mercury as possible using a 5ml or 10ml syringe. Experimentation will be necessary to find the best angle to draw the heavy mercury into the tube. Use a piece of card to gather the droplets together if they are finely divided. Collect any broken glass and other debris into a suitable container. Use card rather than gloved hands if there is broken glass. Small pieces of broken glass which are uncontaminated by mercury are best disposed of in a sharps disposal box. Mercury spill kits are available commercially; they should normally only be used by a competent person.
- Put the syringe and any other container into which contaminated debris has been collected into double plastic bags. Tie the necks of the bags, label the package “Danger — Mercury. Do not touch”, and put it in a safe place pending collection.
- If a sphygmomanometer has survived relatively intact, apart from spillage of mercury into the case, protect any sharp edges by wrapping in sticky tape to avoid tearing holes in the bag, put the whole instrument into a plastic bag, tie the bag at the neck, label it as above, and put it in a safe place pending collection.
- Do not use a vacuum cleaner on residual mercury; this can produce high vapour concentrations. Only dispose of mercury as hazardous waste.
- Report and investigate the incident.
- Mercury: COSHH Guidance for Managers in the NHS, BOHS. (Pdf)
- Mercury: General Information, Incident Management and Toxicology, Public Health England
- Mercury in Measuring Devices: Guidance Note, Environment Agency