13 November 1997 Coping in a chemical world: toxic gases

We live in a chemical world but there is probably no chemical so toxic that we cannot work with it safely, says Lincoln University toxicologist Dr Ravi Gooneratne.

The science experiment that went wrong at a Christchurch high school earlier this year, making over 100 students sick, highlighted the need to comply with health and safety guidelines when working with chemicals.

Hardly a week goes by without hearing about a chemical that proves fatal or potentially threatens our health. Remember the three Christchurch teenagers tragically gassed in their car at Arthur's Pass at Anzac weekend? What's the lesson from that for the holiday season ahead? And of course how did you survive winter in the Garden City where the ‘toxic gas’ component of the city's infamous smog impacts on all and inevitably threatens the lives of many.

Following safety guidelines is especially important when working with chemicals including gases, which are colourless and odourless at low concentrations, but can still be toxic at such levels.

Anything toxic can frighten people. Should you be frightened about chemicals? I think not, let me explain. In daily living we are exposed to many chemicals. Over 100,000 chemicals are currently produced worldwide with about 1000 chemicals added each year. The public is generally suspicious of chemicals. They fear poisoning from chemicals, believing all of them to be hazardous. This is not true. A chemical becomes hazardous only when it is not handled properly. Even the most toxic chemicals when used with due care and attention to safety procedures, by or under the supervision of trained personnel, pose little risk to health.

Although sulphur dioxide gas was the culprit in the high school accident, there are several other gases and chemicals we are exposed to at low to moderate concentration, not only at schools, but also at home, in offices and outdoors that can cause toxic effects.

Outdoors, we are exposed to a variety of chemicals including gases and small particles released into the atmosphere from household fires (open fires, wood burners mostly) and motor car exhausts. They can cause eye, nose and throat irritation and make you more susceptible to respiratory infection, bronchitis, asthma and some may also cause cancer.

At the 1997 Canterbury Medical Research Expo, held in Christchurch, Dr Ian Town, a respiratory physician at the Christchurch Hospital, and Dr Neil Cherry, a senior lecturer in meteorology at Lincoln University showed a direct relationship between air pollutants and an increase in respiratory health problems, especially in those with heart and lung diseases.

We spend over 80% of our time at work, at school, or at home. Therefore indoor air quality has become an important health issue because in those places we could be exposed to chemicals at a higher concentration than outdoors especially during winter months when we close doors and windows to conserve heat. We are exposed not only to toxic gases from open fires and solid fuel burners, but also perhaps to nasty chemicals such as lead (from paints) and asbestos if you are living in an old home.

Most of the toxic gases such as carbon monoxide, sulphur dioxide, and nitrogen dioxide to which we are exposed, both indoors and outdoors, are released from fires, burners, heaters, stoves and also from motor vehicles. Among these, the most toxic is carbon monoxide. It is a major pollutant in Christchurch and accounts for over 75% of the city's total emitted pollution (more than 90,000 tonnes per year).

Carbon monoxide gas interferes with the delivery of oxygen to body tissues. At low levels it can cause tiredness, weakness and a headache. Exposure to higher concentrations can cause confusion, dizziness, nausea and seizures. Carbon monoxide poisoning is often a major problem in fire victims with smoke inhalation. High concentrations can comatose and kill you. The deaths of the three teenagers at Arthur's Pass who slept inside a car with food cooking on a burner show how deadly this gas is.

Sulphur dioxide gas is a colourless, irritant gas with a strong suffocating odour. At low concentrations it can produce asthma attacks and a chronic cough. At high concentrations it irritates breathing passages and cause a cough and dryness of throat, and breathing difficulties by constricting airways. Chronic exposure can cause death by asphyxia.

Nitrogen dioxide gas causes irritation of eye, nose, throat and skin. Breathing difficulties may occur with high exposure. Recovery from a high exposure may be slow with a possible relapse and permanent lung damage.

Ozone is another gas we could be exposed to on smoggy days. Indoors, ozone is emitted from photocopiers. Prolonged exposure to even small amounts of ozone can lead to lung damage, shortness of breath and aggravate respiratory diseases.

At home, in addition to these gases, we are exposed to a variety of organic gases and also vapours from household cleaners, disinfectants, air freshness, moth repellents, paints, paint strippers, wood preservatives, car-care products, petrol and engine oils. All these can affect our health but are not usually much more than a nuisance except in asthmatics and those with lung problems. You are most likely to notice irritation in your eyes, nose and throat but more serious problems can be headaches, wheezing and coughing.

One of the most troublesome organic vapours in recent years has been formaldehyde. A major source of formaldehyde is the glue which bonds some plywood wall panelling, particleboard and fiberboard. Concern over formaldehyde emissions first became a public issue in 1990 when over 40 new homeowners in Christchurch reported skin rashes and allergic respiratory problems.

For New Zealand as a whole there are no strict guidelines in force to reduce the major atmospheric pollutants from open fires and solid fuel burners that account for the bulk of particulate pollution during high pollution periods.

As for indoor air pollution, adequate ventilation will keep many pollutants within safe limits. To prevent a build-up of toxic gases inside houses and buildings, it is also important to keep gas appliances properly adjusted, keep flues open and also keep solid fuel fires hot enough to make sure the gases are carried up the flue.

Hopefully the high school ‘toxic gas’ incident has prompted all educational institutions to review policies and implement safe laboratory procedures to prevent such an event occurring again. Laboratory skills are an essential part of science programmes. Our students need to understand science in a practical way so they can think intelligently and experiment about questions that face them in life.

In summary, we are exposed to many toxic chemicals including gases such as sulphur dioxide, nitrogen dioxide, carbon monoxide, ozone, and vapours such as formaldehyde, at home, at work, at schools and also outdoors. When indoors, good ventilation is essential for healthy living to keep the toxic chemicals within safe limits. When doing laboratory experiments, which are essential in science education, safety is of paramount importance.

Dr Ravi Gooneratne is a Senior Lecturer in toxicology at Lincoln University. He has recently been admitted a Fellow of the Royal College of Pathologists (FRCPath) in Britain.

Ian Collins, Journalist, Lincoln University, Canterbury, New Zealand