Under the Microscope: We produce huge amounts of waste each year, so working out the best way to deal with it has to be a priority, writes Prof William Reville.
Incineration is one option, but it is intensely unpopular with many people, who fear the possible effects of toxic emissions, particularly of dioxins, from incineration plants.
My colleague Prof James Heffron, who is director of the biochemical toxicology laboratory at University College Cork, tried to deal with some of the issues in a recent public lecture.
As he explained, the EU ranks methods of dealing with waste in order of their desirability. First comes prevention, then minimisation, reuse, recycling, incineration and disposal in landfills. We in Ireland have a poor record of implementing the preferred options: little more than 10 per cent of household and commercial waste is recycled or reused.
Incineration has been prominent on the Irish waste-management agenda for many years. Both incinerators and landfills emit toxic chemicals, but the EU prefers incineration, which it regulates. Nevertheless, the Irish particularly dislike incineration.
Technically, incineration means the controlled burning of material at temperatures of at least 1000 degrees; any emissions are cooled and cleaned before they are released to the atmosphere.
Burning material in a domestic fire or in a barrel in the garden, by way of contrast, occurs under uncontrolled conditions at relatively low temperatures - between 200 and 400 degrees - and the gases and particles that are emitted disperse freely into the atmosphere. (Incineration of toxic industrial waste also leaves a small residue of highly toxic ash. There is general consensus that this residue is best stored in a special toxic-waste repository.)
The main emissions from incinerators are carbon dioxide and water: harmless to human health. But they also emit minor amounts of toxic organic compounds (including dioxins), inorganic gases (carbon monoxide, hydrogen chloride, hydrogen fluoride, nitrogen oxide and sulphur dioxide) and toxic metals (arsenic, cadmium, lead and mercury). The EU limits their concentrations to levels that pose insignificant threats to human health.
The public is mainly concerned about emission of dioxins, which can cause cancer, damage the immune system and, at certain concentrations, interfere with fetal development. But dioxins are emitted from modern incinerators at almost unimaginably low levels: less than 0.1 nanograms per cubic metre (a nanogram is a thousand-millionth of a gram).
It is sometimes wrongly claimed that dioxin is the most toxic chemical known. The most toxic chemical, easily, is the toxin produced by the food-poisoning bacterium Clostridium botulinum. This is the active ingredient in Botox.
The EU defines air quality in terms of acceptable concentrations of pollutants. Toxic components in the atmosphere are assigned a figure called acceptable daily intake (ADI) - that is, the amount we can take into our bodies each day over 70 years without damaging our health. The World Health Organisation has set the ADI for dioxins at between one and four picograms (a picogram is a trillionth of a gram) per kilogram of body weight per day.
It might be thought that setting ADI levels is a somewhat cavalier approach. Why not specify zero levels of toxic chemicals in emissions? Indeed, green activists often demand this. Unfortunately, zero levels of risk are scientifically unachievable.
Also, in many cases, trying to approach zero is not only highly impractical but also a gross waste of money.
In our daily lives we take certain levels of risk in our stride. We drive our cars, for example; we also fly abroad, play rugby and so on. We evaluate the benefits of these activities, take sensible precautions to minimise the risk and then carry on with a light heart. This is also how we should approach waste.
Regardless of our best efforts, we will always generate waste that must be disposed of, and incineration is probably the best option for some of this waste. We must first of all ensure that we produce waste for such disposal only in the smallest amounts. Then we must take sensible precautions to reduce to an acceptable level the risk to which we are exposed during its disposal.
What is an acceptable level of risk? The scientific consensus is that a risk of death somewhere between one in 100,000 and one in a million is acceptable. To put this in context, the annual risk of death from smoking 10 cigarettes a day is one in 200, from driving a car one in 8,000, from playing soccer one in 25,000, from murder one in 100,000 and from being hit by lightning one in 10 million.
The increased risk of contracting a fatal cancer from dioxins emitted by the incineration of 100,000 tonnes of waste a year, such as is proposed for Ringaskiddy, in Co Cork, is between one in 200,000 and one in two million.
William Reville is associate professor of biochemistry and director of microscopy at University College Cork