Resources - Safety Info

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From December 1992 edition of ‘Crucible’ Volume 23.6

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Introduction
There are millions of chemicals cited in the scientific literature and thousands more are being added every year. There is a lot of uncertainty and debate about the human health impacts of any particular chemical. Of the seven major metals know to Greeks, Mercury has been poisoning its industrial users for thousands of years. The ancients, being no fools, realized the danger and reserved exclusive space in the mercury mines for slaves, convicts and other undesirables. Life was short, and from all accounts, hellish; a miner seldom survived more than three years.

Description
Elemental Mercury is silvery, odourless, and untarnished. It is the only metal to remain liquid at room temperature that does not react readily with air. The glittering skittish mercury was ascribed magical properties and became a favourite of the early doctors, jewellery-makers and, especially, the alchemists. The medieval alchemists were also fascinated with mercury, or quicksilver, as it was more commonly called. They believed mercury to be the primary constituent of all metals. Gold, silver, copper, tin, lead and iron were each supposedly an amalgam of mercury, with different proportions of sulphur and other contaminants mixed in. And, in a more literary vein, Lewis Carroll’s irrational and excitable Mad Hatter was undoubtedly poisoned by the mercury used to treat the furs in some fictitious hat factory in Wonderland. Certainly hundreds of men and women who cut felt or shaped hats in very real factories at the turn of the century were seized by very real tremors, psychological problems and aggressive mood swings.

Uses
Because of its unique properties, elemental mercury has many uses: the greatest use of elemental mercury in Ontario, is in electrical equipment, such as alkaline batteries, fluorescent light bulbs and "silent switches". Mercury and its compounds are used in extraction of gold and silver. It is also used in medical and scientific instruments such as thermometers, manometers and barometers, jewellery making and for coating the backs of mirrors. It is still widely used in dental amalgams, as a catalyst in the production of polyurethane foams, and in printing.

Common Types of Mercury
Alkyl Mercury Compounds (e.g. methyl mercury), are a class of especially toxic organic mercury compounds, and used minimally in Ontario, primarily in research institutions.

Inorganic Mercury Compounds are used as preservatives and stabilizers in some latex paints, oil-based exterior paints and caulking compounds. They are used in leather tanning compounds, photographic chemicals, pesticides, explosives and as catalyst in chemical manufacture, although these uses are declining. Inorganic mercury compounds have also been used in several drugs and medicines, antiseptics, skin ointments and diuretics.

The Regulation
The regulation respecting Mercury, Ontario Regulation 141/82, was filed with the Registrar of Regulations on March 9, 1982. The assessment came into force on the date of filing; the control measures came into force on June 7, 1982. Mercury has been placed under the designated substance regulations. Designated substances are biological, chemical or physical agents for which worker exposure is prohibited or regulated.

With two major exceptions, the regulation applies to every employer and worker at a workplace where mercury is present and at which a worker is likely to inhale, ingest or absorb mercury. The two exceptions, to whom the mercury regulations does not apply, are:

• dentists and workers in dental offices, and
• constructors, employers carrying out construction projects and workers working at construction projects.

The exposure of a worker to mercury must not exceed the limits specified in the regulation TIME WEIGHTED AVERAGE EXPOSURE VALUE (TWAEV). The time-weighted average exposure of a worker to all mercury except alkyl mercury compounds must not be greater than:

• 0.05 milligrams per cubic metre (mg/m3) of air averaged over an eight hour day or forty hours a week.
• The time-weighted average exposure of a worker to alkyl mercury compounds must not be greater than 0.01 mg/m3 of air.

MAXIMUM EXPOSURE CONCENTRATION:

The maximum exposure (Short-Term Exposure Limit C STEL) of a worker to all mercury (except alkyl mercury compounds) must not be greater than 0.15 mg/m3 of air at any time.

The maximum exposure to alkyl mercury compounds must not be greater than 0.03 mg/m3 of air at any time.

Exposure at the STEL must:

• not last longer than 15 minutes.
• not occur more than four times in a day.
• be at least one hour since last exposure at that level.

ROUTES OF EXPOSURE
Mercury may enter the body through inhalation, skin absorption or ingestion and cause serious damage to a number of systems in the body.

Inhalation
Most occupational exposure to mercury vapour in the workplace occurs through breathing in airborne vapours and dusts. Workers may not be aware of the presence of mercury vapour in the workplace because it is odourless and colourless.

About 80% of inhaled mercury vapour can pass from the lungs into the blood stream and be carried to other parts of the body.

Skin Absorption
Most forms of mercury can be absorbed into the body through direct contact with the skin, but it is not known to what extent absorption occurs. It is suspected that alkyl mercury compounds are absorbed to a greater extent than are elemental mercury and inorganic mercury compounds.

Ingestion
Ingestion may occur when workers consume food and drink, chew gum or smoke cigarettes that have been brought into the work area and have become contaminated with mercury. The degree to which ingested mercury is absorbed into the body through the gastro-intestinal tract depends on a number of factors, including diet and the solubility of the ingested substance. Elemental mercury and inorganic mercurous compounds' solubility and the extent of absorption is fairly low. Organic mercury compounds are much more readily absorbed than inorganic compounds.

HEALTH HAZARDS
Mercury may be the only chemical for which the human health effects data, both chronic and acute, surpasses in both quality and sheer volume the lab animal data. Indeed, the availability of so much good human health documentation seems to have discouraged further long-term animal studies. The medical effects are explicit though insidious; they are often confused with other emotional or health problems, including stress.

Elemental mercury is highly toxic and the brain is the critical site for chronic mercury exposure. Inhalation of high concentrations of mercury vapour for relatively brief periods can cause pneumonitis, bronchitis, chest pains, dyspnea, and coughing as well as stomatitis, gingivitis, salivation and diarrhoea.

The soluble mercuric salts, such as the bichloride, as well as mercuric oxide, are highly poisonous on ingestion, with oral LD50 of 1.0 to 18 mg/kg.

Mercurous compounds are less toxic by oral administration, due to the formation of sparingly soluble mercurous chloride in the stomach.

Acute Exposure
Mercury compounds at high levels cause a variety of gastrointestinal symptoms and severe anuria with uremia. Acute poisoning results in mild to severe erosion of the gastrointestinal tract, nausea and vomiting, bloody diarrhoea and shock.

Chronic Exposure
Chronic exposure to Mercury involves the central nervous system, with tremor and erethism C an abnormal state of emotional instability and various neuropsychiatric disturbances, weakness, insomnia, fatigue, loss of appetite and corresponding weight loss, loss of hand-eye coordination, tingling or prickling of the skin, and problems with the sense of taste or smell. Nosebleed and nasal inflammation were reported by the exposed workers to a significant degree. Neuropsychiatric changes also appeared to be related to the amount of mercury absorbed. It will cross the placenta in pregnant workers and accumulate in the fetus: severe brain damage has occurred in children whose mothers consumed large quantities of methylmercury-contaminated fish. It also accumulates in the kidneys and liver. Other symptoms include proteinuria, inflammation of the mouth and excessive salivation. A common effect of chronic methylmercury poisoning is constriction of the field of vision. This usually irreversible symptom, when combined with a loss of reasoning power, can put the victim completely out of touch with reality.

ASSESSING AND CONTROLLING EXPOSURE TO MERCURY

The Assessment
To assess the extent to which workers are exposed to mercury, note all processes involving mercury and the forms in which mercury is likely to be released into the workplace. Particular attention should be paid to the possibility of spills and leaks of mercury as these can be major sources of contamination. If mercury is present in sealed equipment, the possibility that the equipment may break or leak should be assessed. If spills or leaks are not cleaned up thoroughly and immediately, it can lead to a steady release of mercury vapour into the air. Note the visible droplets of mercury around equipment, on floors, on surfaces and clothing. Type of floor covering and its potential for retaining spilled mercury, as well as cracks and crevices should be noted.

If it appears likely that mercury has been spilled in the workplace, the assessment should include air monitoring as spilled elemental mercury will continue to release vapours. The rate at which mercury vaporizes increases markedly with an increase in temperature.

The conclusion of the assessment should comment on whether there is a possibility of a mercury spill and the effect such a spill would have on the health of workers.

The Control Program

Engineering Controls:
These are the most effective ways of reducing exposure. It can be achieved by the following measures.

Product Substitution --- It may be possible to eliminate mercury from the workplace by replacing it with a less toxic material.

• Substitutes may be available for mercurial compounds used in pesticides, fur and leather treatment, bulb dipping and other processes.
• Scientific and medical instruments that contain mercury may be replaced by instruments that use alcohol or that are operated electronically.
• If mercury-containing instruments are used, floor or wall models rather than table-top models should be chosen, to reduce the likelihood of breakage.
  

Enclosure/Isolation --- Any equipment or process in which mercury is used should be designed to make sure that the mercury does not escape into the atmosphere through leaks, breakage or spills.

• Areas of the workplace where mercury is used should be segregated from other areas and restricted to workers directly involved in mercury operations. Such operations should be enclosed in the smallest convenient space and be adequately ventilated.
• Processes involving the handling of mercury should be conducted in ventilated glove boxes or fumehoods.
• Mercury should be stored in air-tight containers to prevent vapours from being emitted into the air. Containers of mercury should be stored in ventilated fume cupboards.
• Covering the mercury with a layer of water or oil is a temporary measure to slow the rate of vaporization.
• Processes such as filling mercury-in-steel thermometers must be thoroughly enclosed, and regular maintenance must be performed to prevent leaks.

Workplace Design:
The construction of surfaces, floors, fixtures and equipment is very important in facilitating clean-up and recovery of mercury. The following features will help to promote thorough recovery:

• Surfaces should be smooth and free from joints, cracks and recesses. They should be made of materials that are impervious to mercury and that do not amalgamate with mercury. Woodwork and porous brick should be avoided.
• Do not use floor carpeting or tiles in areas where mercury is handled.
• Floor covering should extend about six inches up the walls to eliminate the crack between floor and wall in which spilled mercury can be trapped.
• Surfaces and floor should be of a colour that makes it easy to detect droplets of spilled mercury.
• Floors should be sloped away from the worker towards a trough containing water or oil and should be attached to the work bench to catch spilled mercury.
• Floor heating, which promotes vaporization of spilled mercury, should be avoided.

SPILL CLEAN-UP
Stringent measures to clean up spilled mercury are an essential part of any control program. Clean-up procedures should be written, thoroughly explained to all staff working with mercury, and posted in the workplace.

If it is not thoroughly cleaned up, metallic mercury may remain on floors and surfaces or become trapped in crevices where it may continue to release vapour into the air for a long time. When liquid mercury spills, it tends to divide into small globules. The greater the number of these globules, the more vapour will be released into the air. Therefore, it is important not to use clean-up methods that would tend to break the mercury into smaller droplets. Small spills of mercury should be cleaned up immediately with a vacuum cleaner equipped with a charcoal filter or water trap, or a hand-held pipette used with a rubber bulb or water pump. Surfaces should then be washed with a mercury-neutralizing solution such as 20 per cent calcium sulphide or 20 per cent sodium thiosulfate. If the mercury has broken up into globules, sulphur powder can be sprinkled over the area immediately after the spill occurs to prevent the mercury from vaporizing before the clean-up is complete. Appropriate protective clothing must be worn when cleaning spills.

If there is a possibility that a major spill of elemental mercury can occur, the control program should designate a person responsible for supervising emergency procedures and clean-up and the following steps should be taken:

• Evacuate all people from the area of the spill.
• Contain the mercury vapour in the smallest area possible by closing all doors between the spill area and the rest of the workplace and shutting off any ventilation equipment that circulates air from the spill area to the rest of the workplace.
• Post signs warning of the spill and forbidding entry to the spill area.
• Appropriate respiratory protection and protective clothing must be worn before entering the spill area.
• Assessing the extent of the hazard by determining the quantity of mercury that has spilled; taking the reading of mercury vapour concentrations with direct reading instruments like dragger tubes, calorimetric indicators that use detector tubes or strips of paper that turn colour on contact with mercury; assessing ventilation in the spill area; and determining the temperature in the spill area to assess the vaporization of mercury.
• Ensure that everyone involved with the clean-up is aware of proper procedures and the hazards of mercury and are equipped with proper protective clothing.
• Collect all visible spilled mercury with a vacuum device equipped with a charcoal filter or a water trap, making sure all mercury trapped in cracks and crevices is picked up.
• Wash the spill area with a neutralizing solution like 20 per cent calcium sulphide, 20 per cent sodium thiosulfate, that will convert the mercury into a form that will not vaporize.
• After the spill has been cleaned up, monitor the air again for mercury concentration. If levels are high, repeat vacuuming and neutralizing procedures.

DISPOSAL
Waste mercury or mercury-contaminated waste must be stored in air-tight containers or covered with water or oil and kept in a cool environment. It must be disposed of in accordance with the requirements of the Ministry of Environment.

FIRST AID
If the chemical gets into the eyes, irrigate immediately. If skin contact is made, wash with soap at once. If inhaled, move the victim to an area of fresh air and perform artificial respiration and transfer promptly to a medical facility. If swallowed, summon medical help, give large quantities of milk or water and induce vomiting.

CONCLUSION
The school (and or board) must decide whether to ban or use mercury. If mercury is used in the school or board then you must have a spill procedure.

The difficulty with the act is to distinguish between a large and small spill. There is no absolute decision by any regulatory bodies but a suggested guide is: Small spill, 1 B 2 thermometers; Large spill, 12 thermometers.

BIBLIOGRAPHY

• Designated Substances in the Workplace: A Guide to the Mercury Regulation. Occupational Health and Safety Act.
• Mercury. Hazardous substances fact sheet. New Jersey Department of Health.
• Documentation of the Threshold Limit Values and Biological Exposure Indices. 5th ed. ACGIH. 1986.
• Glenn, W. Mercury: To Those Who Ignore History. OH&S Canada. Vol. 4.
• Fundamentals of Industrial Hygiene. 3rd edition.