Retorts

Deadly Air

Dr Janine Clemons presents an interesting view on the "deadliness" of air in New Zealand [Is Our Air Deadly?, October]. This is an important subject, and I'd be the first to promote its discussion in scientific and public literature.

However Dr Clemons' analysis is somewhat emotive, and contains some rather unfortunate errors and misconceptions which I feel cannot go unchallenged. I do not want to denigrate in any way her major point about the potential toxic effects of particulates needing more research and analysis, but I was a little disappointed to note that she has presented no analysis on the likely scale of effects in New Zealand, nor on the substantive reasons why research on these topics is difficult, especially in New Zealand.

Firstly there are a number of minor errors, such as:

• there is hardly any SO₂ in New Zealand, except for localised industrial emissions in Christchurch, and perhaps Dunedin
• incomplete combustion is not the only significant cause of vehicle emissions
• domestic coal use contributes as much, if not more, to PM₁₀ than wood use
• the toxic effects of particulates are not "recent" but have been known since the 1850s at least
• Canterbury Regional Council has never said "...air quality problems in New Zealand rival those of London or Birmingham..." -- they do not
• Auckland does not have a "constant sea-breeze" blowing pollution away

In the table presenting air quality guidelines, there are several serious errors. The WHO guidelines quoted are wrong -- lead 3-month average is 0.5 109g m^-3 not 1.5, NO₂ does not have an 8-hour guideline, and the 1-hour is 200 109g m^-3 not 300, and the NO₂ 24-hour level has been removed, CO 1-hour is 30,000 109gm^-3 not 40,000. Readers can easily check these out at http://www.who.int. It is also relevant that (a) the CRC has its own guidelines which are different from the New Zealand guidelines (these should be shown -- for instance the PM₁₀ 24-hour guideline is 50 109gm^-3 not 120), and (b) the New Zealand guidelines are currently under review and may be changed in 2000.

The reasons given for the WHO being "reluctant to state guidelines for particulates" are not because they find it "too complex", but because research has shown there is no lower observable effect limit for PM₁₀. Any discussion of risk analysis of effects of particulates should surely recognise this fundamental precept.

Also of concern is the implication in the paper that inadequate attention has been given to toxicological research in New Zealand, but with no discussion on the reasons for this. As anyone with even modest toxicological or epidemiological experience will know, there are two main reasons, each of which make effective research in New Zealand very difficult.

The first is, as always, funding. It can be hugely expensive because of the complex sampling and analysis techniques, and the need for large amounts of ancillary information. However more fundamentally, such research needs large sample numbers. New Zealand's 3.8 million people simply do not provide a big enough base for such work. A recent analysis of the effects of particulates in Christchurch by Dr Simon Hales and others at Wellington Medical School has used 10 years of monitoring data, and effects on the 300,000+ population of greater Christchurch. These datasets are only just large enough to produce a statistically meaningful result.

Thus when Dr Clemons suggests that current PAH monitoring programmes need to include monitoring of biological and health effects, I do question the cost-effectiveness of this and worry about our ability in New Zealand to contribute much to the understanding of any effects. I think we need to spend our taxpayer-sourced money on:

• determining just what the current PAH concentrations (and other toxic substances) are across the country (basic monitoring)
• a close watch on international research to continually assess whether New Zealand is likely to have any problems, and the scale of these (risk assessment)
• continuous development of proactive and practical policies and legislation which keep New Zealand as clean as possible (risk management)

I do appreciate [your] attention to these issues, which are becoming of more interest and concern to people in New Zealand. However I hardly think readers should be left with the impression that New Zealand's air is all that "deadly"!

Gavin Fisher, Senior Air Quality Scientist, NIWA

Dr Janine Clemons is overseas, and will respond to this letter in the next issue.