- Mercury is a virulent poison that is readily absorbed through the respiratory tract or through unbroken skin. It acts as a cumulative poison since only small amounts of the element can be eliminated at a time. The present accepted threshold limit for Mercury in air is 0.05 mg m-3. (NB. air saturated with mercury vapour at 20°C exceeds the toxic limit by 100 times). High concentration of vapour may cause a metallic taste, nausea, abdominal pain, vomiting, diarrhoea and headache. Chronic effects from continual exposure to small concentrations can cause severe nervous disturbance, insomnia, loss of memory, irritability and depression. Loosening of teeth, dermatitis and kidney damage are possible in severe prolonged absorption.
- Mercury can react with ammonia to produce an explosive solid. It can cause severe corrosion problems because of its ease in forming amalgams. Reacts violently with dry Bromine
- Mercury may be transported only in small quantities in plastic containers (glass bottles are unsuitable because breakages will result in possible spillage over a large area).
- Mercury may be handled only in a fume-hood and over a suitable plastic tray (mercury may react with a metal tray or may be absorbed into a porous tray e.g. wood).
- Skin contact should be avoided. Wash hands thoroughly after using mercury
- Secondary containment must be used on all apparatus containing Mercury e.g. manometers, McLeod gauge, Mercury switches, Mercury diffusion pumps (generally phased out in favour of the safer oil diffusion pump). Care must be taken with mercury in glass thermometers.
- As for all other vacuum pumps, the exhaust from vacuum pumps on systems containing mercury must always be vented either to the outside or into a ducted fume-hood.
- All spillages must be cleaned up immediately using the recommended methods and the equipment kept solely for this purpose. When spilled, Mercury breaks into many small droplets covering a large area: avoid spreading the contamination by restricting access to the spill area and only use the designated cleaning tools (e.g. brush, floor mop or dustpan).
- If mercury has spilled onto a hot surface (hotplate, mantle, heating element) evacuate the room as high concentrations of vapour could be present.
- TO MINIMISE CONTAMINATION USE ONLY SPECIAL EQUIPMENT KEPT FOR MERCURY DECONTAMINATION AND DO NOT USE THAT EQUIPMENT FOR ANY OTHER PURPOSE.
- Spillages should first be cleaned up as far as practicable by mechanical means, e.g. by either the special hand operated sucker, or, for larger spills, by using the vacuum trolley designed for the purpose. Areas that have been affected by fine droplets of mercury (or have been identified as being contaminated by the Mercury "sniffer" meter) should then be treated with a slurry composed of equal parts of slaked lime (calcium hydroxide) and flowers of sulphur mixed with enough water to make a yellow wash. The slurry should normally be left in place for between 24-48 hours after which it should be cleaned away by careful sweeping with a dustpan and brush prior to washing with water to remove all traces of the slurry (often several washes).
- Before the area may be used again it is essential that a second "sniffer" test be performed to make sure that the contamination has been removed. Occasionally a second application may be found to be necessary. Equipment must be decontaminated after use.
Disposal of Waste
- Dirty liquid mercury should be carefully transferred to a clearly labelled plastic bottle and added to the chemical waste.
- Slurry and contaminated items e.g. tissues and small bits of broken glass (thermometer) should be sealed in a suitable, clearly labelled container.
Level of Risk Remaining
This should be low if the procedures outlined here are followed although it should be recognised that parts of the Department of Chemistry may be contaminated with mercury from its careless use in the past.