The recently released report by Professor Sir Peter Gluckman, on the treatment of dwellings in which meth (methamphetamine) has been used, has almost immediately lead to a more relaxed approach to possible contamination – in particular by Housing New Zealand. The fiscal implications of the report are very significant – its conclusions suggest that tens of millions of dollars have been wasted on unnecessary decontamination, and tens of millions of dollars also stand to be saved going forward. For that reason, the report is a shock to the decontamination industry, and there has been a hostile response in some quarters. The report needed to be robust enough to withstand such a response and I think it is. I have not read the report in its fine detail, but it looks to be a thorough analysis which has been appropriately informed by and tested with experts both from New Zealand and overseas.
In releasing the report Professor Gluckman used an interesting set of words – in essence he said that there was “no current evidence that there is a health risk posed by dwellings in which meth has been used but not manufactured”. This is a very negative statement and it would be preferable to be able to be more positive and say (for example) “the evidence available shows that there is no health risk etc…”. But the evidence clearly does not support such a statement and begs the question of whether new evidence might be found or developed which contradicts the position taken in the report. The report indeed notes specifically that “the absence of evidence is not evidence of absence of an effect.” It consequently states that there is a clear need for more research and a coordinated inter-agency effort to build up a robust dataset. This commented on further below.
A question that remains to be answered, given that the Gluckman report conclusions did not come as a great surprise to anyone with technical knowledge in the meths contamination area, is that of why the relevant agencies let this situation develop? It transpires that Housing New Zealand was the most culpable agency, as it applied the Ministry of Health standards in a way that was not only inappropriate but really incomprehensible. You wonder why the Ministry of Health did not “blow the whistle” as they must have surely known about the Housing New Zealand approach and its financial implications. In the end it took the independent report by Professor Gluckman, which was commissioned by the Minister, to return some sanity to the situation.
I think that a significant contributory factor to the inaction of the Government agencies involved in such situations is that they are pushed to be risk averse, and that is particularly so if human health and safety is at issue. The problem is that the balance of risk and reward is very asymmetric – in other words the penalty (for the agency) for being too conservative is relatively minor (meth contamination turns out to be the exception because of the Gluckman report) whereas the penalty for dealing with risk in a more balanced way and adverse human health and safety effects being even suspected as a result, is likely to be very much stronger. Hence the inclination to be conservative.
In reality risk assessment of human health effects from chemicals is subject to inherent uncertainty and this is demonstrated quite nicely by the Gluckman report.
In assessing human health risk there are two elements to be considered – the toxicity of the chemical (or substance) and the mechanism for and level of exposure. Both elements are subject to uncertainty.
On the face of it the toxicity of a substance should be easy to measure. Toxicity (or degree of hazard) is also a matter on which there is international consultation and, for many if not most substances, a scientific consensus. In practice there is some (or in some cases considerable) uncertainty about toxicity to humans and this arises in part from the difficulty of obtaining direct experimental evidence. It is not ethical (or lawful I think) to carry out experiments involving humans, if there is any significant risk of causing harm. Traditionally toxicity has been measured by carrying out experiments on animals and then extrapolating the results to apply to humans. The need to extrapolate introduces some uncertainty and this is compounded by the need to obtain a measurable effect in the test animal. Even this route to measuring toxicity is being closed off, with understandable concern about the welfare of the animals involved. Fortunately, there is already a solid international data base on the toxicity of most chemicals, and new chemicals can often be reasonably well assessed for toxicity by looking at their chemical similarity to chemicals with known toxicity.
A further issue is that of lack of data on the impact of levels of exposure to the chemical which are less than that causing death. In practice these are the levels which are often of most concern. It is not commonly appreciated that almost all chemicals can be toxic if the exposure is sufficiently high, and this includes chemicals which are naturally present in the human body. A favourite example is common salt. Salt is present in the normal diet of humans and in the human body. However, if ingested in sufficient quantities it can cause death. Another example is fluoride which in low concentrations has positive effects on preventing tooth decay but is a poison in high concentrations. So, the issue is rarely simply that of whether or not a chemical is toxic, but rather the level and mechanism of exposure to the chemical which is likely to cause harm (or at the extreme, death) in humans.
There also may be uncertainty about the mechanism of exposure which is most appropriate to particular risk situations. Mechanisms can include ingestion (eg eating contaminated food), absorption through the skin, or absorption through the lungs (breathing contaminated air). This particular uncertainty is commonly dealt with by taking worst case situations, but the test of reasonableness still applies. For example, if there is no reasonable chance of the chemical being ingested, then it may be unreasonable to take this as a worst case even if ingestion poses the greatest chance of an adverse effect. In the case of meth contamination, it can be fairly said that the stance taken by Housing New Zealand was clearly unreasonable.
These uncertainties are commonly dealt with, amongst other things, by applying a safety factor, which can be as high as hundreds to one if there is a high level of uncertainty and the chemical is toxic at relatively low levels of exposure. The level of the safety factor is in the end a matter of judgement. In general, the higher the uncertainty and the greater the toxicity of the chemical, the higher is the safety factor adopted.
These uncertainties do not prevent analyses being developed which produce a robust response to particular risk situations. The Gluckman report very clearly falls into this category, the qualification in the conclusions on “absence of evidence not implying absence of effects” notwithstanding.
This is another of Bas Walker’s posts on GrownUps. Please look out for his articles, containing his Beachside Ponderings.