MERCURY AND MERCURY POISONING - THE CONTROVERSIAL ELEMENT (THE APPLICATIONS AND DANGERS OF MERCURY)

Virtually all metals exist as solids at room temperature. Mercury is the only metallic element that is a liquid under normal conditions. If cooled to 39°C, it does freeze to a solid. Liquid mercury is shiny and metalliclooking.

You have probably heard a fair amount about the toxicity of mercury. As a liquid, it is not especially toxic when swallowed since most of it passes through the body unchanged.

However, mercury vapor is highly toxic, as are all compounds of mercury that dissolve in water to form solutions. Once they enter the body, these forms of mercury can attack the brain and produce mental and physiological disturbances.

An incident in Texarkana, on the Texas–Arkansas border, illustrated the hazards of handling mercury. Two teenagers stole 40 pounds of liquid mercury from a site where it had been used to make neon lights.

They poured it over themselves and on floors in their homes, gave it out to friends, and even dipped cigarettes into the liquid and smoked them. Within days they began to exhibit the signs of mercury poisoning: coughing up blood, vomiting, breathing difficulties, and seizures.

The end result was that eight contaminated homes were evacuated, a family dog was killed by the vapors, and more than 170 people in the town and surrounding areas received medical treatment for mercury exposure.

Mercury poisoning was much more common in the 19th century when workers who used mercury to cure felt hats developed twitches, spoke incoherently, and drooled as a result of long-term exposure to mercury vapors.

These workers provided Lewis Carroll with a model for the Mad Hatter in Alice in Wonderland. These days, most of the mercury that enters the environment comes from the incineration of waste and sewage sludge, and the burning of coal.

Recently, scrapping cars without removing the elemental mercury used in light switches and other components was identified as a significant source of the element to the environment.

MERCURY DANGERS IN DENTAL CARE?
Until quite recently, an alloy that most people had an intimate acquaintance with was the material used to fill cavities in decayed teeth. You may be surprised to learn that mercury was one of the metals used to fill teeth.

Although mercury is a liquid at room and body temperatures, it forms many alloys, called amalgams, that are solid at normal temperatures. Those having melting points in the 60°C range are useful for fillings, since they can be placed in the decay cavity as a warm liquid metal without causing the patient pain.

The liquid assumes the cavity shape as it cools and solidifies in place. Dental amalgam combines mercury with silver, which imparts resistance to tarnishing and mechanical strength, and about half as much tin, which readily amalgamates with mercury.

When first placed in a tooth, and whenever the filling is involved in the chewing of food, a tiny amount of the mercury is vaporized. Some scientists believe that mercury exposure from this source causes long-term health problems in some individuals, but an expert panel of the U.S. National Institute of Health concluded that dental amalgams do not pose a health risk.

A recent study of adults found that no measure of exposure to mercury—whether the level of the element in the urine or the number of dental fillings—correlated with any measure of mental functioning or fine motor control.

CYANIDES - DANGER OF CYANIDES BASIC INFORMATION AND TUTORIALS

What are the dangers of cyanide?

As a group, the cyanides are among the most toxic and fast-acting poisons. (This is due to the cyanide ion which interferes with cellular oxidation.)

Hydrogen cyanide (prussic acid) is a liquid with a boiling point of 26°C. Its vapour is flammable and extremely toxic. This material is a basic building block for the manufacture of a range of chemical products such as sodium, iron or potassium cyanide, methyl methacrylate, adiponitrile, triazines, chelates.

Toxic effects of hydrogen cyanide 
Concentration in air Effect (ppm)
2–5 Odour detectable by trained individual
10 (UK MEL 10 mg/m3 STEL (SK))
18–36 Slight symptoms after several hours
45–54 Tolerated for 3–60 min without immediate or late effects
100 Toxic amount of vapours can be absorbed through skin
110–135 Fatal after 30–60 min, or dangerous to life
135 Fatal after 30 min
181 Fatal after 10 min
270 Immediately fatal

Although organocyanides (alkyl cyanides, nitriles or carbonitriles), in which the cyanide group is covalently bonded, tend as a class to be less toxic than hydrogen cyanide, many are toxic in their own right by inhalation, ingestion or skin absorption. Some generate hydrogen cyanide under certain conditions, e.g. on thermal degradation.

Depending upon scale of operation, precautions for cyanides include:
• techniques to contain substances and avoid dust formation (solid cyanides), aerosol formation (aqueous solutions), and leakages (gas);
• gloves, face and hand protection;
• high standards of personal hygiene;
• ventilation and respiratory protection (dust or gaseous forms);
• environmental monitoring for routine processes;
• health surveillance.

CARBON MONOXIDE DANGER AND EFFECTS BASIC INFORMATION AND TUTORIALS

What are the dangers of carbon monoxide?

Carbon monoxide
Carbon monoxide is a colourless, odourless gas and – without chemical analysis – its presence is undetectable. It is produced by steam reforming or incomplete combustion of carbonaceous fuels;

Carbon monoxide is extremely toxic by inhalation since it reduces the oxygen-carrying capacity of the blood. In sufficient concentration it will result in unconsciousness and death.

The STEL is 200 ppm but extended periods of exposure around this, particularly without interruption, raise concern for adverse health effects and should be avoided. If a potential carbon monoxide hazard is identified, or confirmed by atmospheric monitoring.

Typical carbon monoxide concentrations in gases

Gas Typical carbon monoxide concentration (%)
Blast furnace gas 20–25
Coal and coke oven gas 7–16
Natural gas, LPG (unburnt) nil
Petrol or LPG engine exhaust gas 1–10
Diesel engine exhaust gas 0.1–0.5

Typical reactions of persons to carbon monoxide in air

Carbon monoxide (ppm) Effect
30 Recommended exposure limit (8 hr time-weighted average concentration)
200 Headache after about 7 hr if resting or after 2 hr exertion
400 Headache with discomfort with possibility of collapse after 2 hr at rest or 45 min exertion
1200 Palpitation after 30 min at rest or 10 min exertion
2000 Unconscious after 30 min at rest or 10 min exertion

PRECAUTIONS IN HANDLING EXPLOSIVES IN LABORATORY

How to handle explosives in laboratory?

Storage
The quantities of potentially explosive materials in store and in use should be strictly limited. Stores should be specially designed, constructed of non-combustible material, and located away from other hazards (e.g. brick ‘coal bunkers’ are suitable for small samples, but purpose-built constructions with explosion-proof lights etc. are required for larger quantities).

They should be designated ‘No Smoking’ areas and be well labelled. Stores should be used exclusively for these materials. Other combustible material such as fabric, paper, organic solvents should not be stored there.

Generally the substances in this class are unstable when heated or exposed to light; they should be stored cool and in the dark. However, for liquids with added stabilizer cooling may cause separation of the material from the stabilizer.

Similarly, precipitation of a potentially explosive compound from a diluent may occur on cooling. In both cases this can represent a hazardous situation.

Stores should be ventilated and sound, e.g. no cracks in floors, no rusty window frames, no water seepages, etc.

Stores should be clean, tidy and locked. Contamination must be avoided and a high standard of housekeeping maintained.

Heat sources should not be permitted nearby.

Material should be purchased in several small containers rather than one large container and always stored in original containers. Integrity of the labels should be checked.

Use
Use must be restricted to experienced workers, aware of the hazards and the necessary precautions. Records of usage should be kept and stock rotated. Old material should be disposed of.

Work should be on a scale of <0.5 g for novel but potentially explosive material until the hazards have been fully evaluated and <5 g for established, commercially available, substances such as peroxide free-radical initiators.

For the above scales, eye protection should be worn and work should be undertaken in a standard fume cupboard behind a well-anchored polycarbonate screen. It is advisable to wear a protective apron and hand protection; whether leather gauntlets or tongs should be used will be dictated by circumstances.

Such measures are recommended but it should be ensured that they do not precipitate a hazard as a result of loss of tactile sensitivity (e.g. dropping a flask, overtightening clamps, exerting excessive pressure when assembling apparatus). The material of gloves needs consideration. (PVC but not rubber is suitable for tert-butyl peroxide.)

For large-scale work, armour-plated fume cupboards are likely to be required. Skin contact, inhalation and ingestion must be avoided. Splashes in eyes or on skin should be washed away immediately with copious quantities of water. Medical attention should be sought. If material is swallowed, medical aid is required immediately.

Glass apparatus should be pickled (e.g. in nitric acid) and thoroughly rinsed after use. Sources of ignition such as hot surfaces, naked flames etc. must be avoided and smoking prohibited where explosives are used.

Accidental application of mechanical energy should be avoided (e.g. material should not be trapped in ground-glass joints): seized stoppers, taps etc. must not be freed by the application of force. To minimize risk of static electricity, laboratory coats of natural fibre rather than synthetic fabrics are preferred.

It is important to neutralize any spillage on the coat immediately, since delay could result in the impregnated garment becoming a fire hazard.

To prevent glass fragments from flying in the event of an explosion, use should be made of metal gauzes to screen reaction flasks etc., or cages, e.g. for desiccators. Vessels of awkward size/shape may be covered with cling film.

Whenever possible a stabilizer or diluent should be used and separation of the pure material should be avoided. Any waste material (and contaminated cloths, tissues, clothing etc.) must be rendered safe by chemical means or by controlled incineration of dilute solution where practical prior to disposal.

In the event of fire, the area should be evacuated, the alarm raised and the fire brigade summoned. Only if it is clearly safe to do so should the fire be tackled with an appropriate extinguisher.

SICK BUILDING SYNDROME BASIC INFORMATION AND TUTORIALS

The chemistry of sick building syndrome.

When working in certain buildings some workers suffer temporarily from a group of symptoms including:

• lethargy/tiredness;

• irritability;

• lack of concentration/mental fatigue;

• headaches;

• nausea/dizziness;

• sore throats;

• dry eyes and skin;

• skin rash;

• asthma;

• blocked/runny nose.

The condition is usually non-specific and seldom traced to a single cause. This has been termed sick building syndrome. Despite much research, little has been proven but the building features associated with the condition are:

• hermetically sealed, airtight shell;

• mechanical heating, ventilation and air-conditioning;

• use of materials and equipment that emit a variety of irritating and sensitizing toxic fumes and/ or dust;

• fluorescent lights;

• application of energy conservation measures;

• lack of individual control over environmental conditions;

• landscape plants;

• VDUs;

• draughts.

Whilst the causative agent(s) have not been established it is thought to be multifunctional and possibilities include physical factors (humidity, temperature, lighting), static electricity, electromagnetic radiation, air ion concentrations, fungi, noise, psychological stress, and chemicals.

Chemicals which are not those involved in the normal work processes can become trapped within the building, albeit at concentrations below those known to cause ill-health effects, if: 

• liberated from materials of construction or furnishings; or

• they could enter from outside.

Temporary problems of building pollution may occur during construction and engineering activities, refurbishment, painting and decorating, and cleaning in internal, or sometimes external, areas. The sources are, generally, more easily traced.