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Prudent Avoidance


Prudent avoidance    M J O'Carroll

Presented to the ADC conference on 28.11.96 with the accompanying paper "Public health concerns about EMFs from electricity supply".


The background paper explains public health concerns in relation to the state of evidence on EMFs, and serves as a public information leaflet. This presentation will draw briefly from it, concentrating on the policy option of prudent avoidance - what does it mean and when is it justified?

As an example we can learn much from [1], consider the Specified Bovine Offal (SBO) ban from the human food chain in 1989. Although there was a BSE epidemic in British cattle, no effect on human CJD was observed although long incubation times would be expected. There was no evidence of association of existing CJD with eating beef products.

- I must pause to reflect on the phrase "no evidence". It is often used in the form "no evidence of a health risk" when there is plenty of evidence but it is not conclusive. With CJD there really was none. Look out for phrases like "no conclusive evidence" or "no persuasive evidence"; they mean the evidence does not meet the stringent criteria for proof - and no known biological mechanism for BSE to transmit to human CJD. The analogy with scrapie was suggestive that it would not. Suspicion of risk to humans was only on the slightest of grounds, but the ban was in principle a cheap and simple hygienic precaution, an example of prudent avoidance. Now of course it is seen as crucial, but marred by sloppy practice and shifty politics. Even now the evidence of a health risk is very speculative.

The term "prudent avoidance" was suggested by Morgan et al t2] as an intermediate approach to decision making in the face of uncertainties about EMFs and cancer. "Prudent" means of modest and well defined cost [3]. The idea was ridiculed [4] as a basis for eliminating any agent to which a hazard has been attributed regardless of validity. A more responsible definition would be: avoidance or mitigation of uncertain hazards, which present rational but inconclusive grounds for suspicion of associated health risks, at zero or low cost commensurate with the potential benefit. The evidence should be assessed and found to give some reason for suspicion while falling short of scientific standards for proof of a cause. Costs and potential benefit need to be considered, recognising the different tolerance to voluntary and imposed exposures [5]. Measures may be interim pending further research, as in the draft NCRP recommendations [6], and may be taken on the personal or collective level. Such a policy is entirely consistent with the precautionary principle.

Turning to residential exposure to EMFs from powerlines, section 13 of the background paper suggests there is broad agreement that cause of cancer is not proven or established, that there is some reason for suspicion which cannot be dismissed, that the evidence does not support firm exposure limits, and that further research is needed. The disagreement is about the strength of suspicion and what to do about it.

Many levels of evidence can be envisaged - spurious, curious, suspicious, suggestive, plausible, persuasive, conclusive. Criteria for causation [71 draw broadly on strength of association and biological plausibility, though no criterion is either necessary or sufficient. NRPB refers to (lack of) persuasive evidence whereas the NCRP draft refers to plausible connections. The background paper outlines the evidence and its assessment.

The scope for prudent avoidance lies in the middle of the range, matching the evidence on EMFs. NRPB's response is to call for urgent research, but not to recommend prudent avoidance. Note that is in the negative; nor does NRPB recommend rejecting prudent avoidance. NRPB's silence is used by government to reject it, yet NRPB's director has stated "The possibility that EMFs may cause cancer cannot however be dismissed. [8].

It would be helpful if NRPB would say positively if it recommends rejecting precaution, if it advises against prudent avoidance at low or even zero cost, and if it advises that local authorities should be prohibited from adopting a precautionary policy even where it reflects public opinion. For that is the effect of NRPB' 6 silence.

The Swedish authorities [9] declared a positive "strategy of caution" short of mandatory regulations, with reference to "normally occurring levels" of EMFs. The table in the background paper shows levels of public concern and reasonable suspicion in context.

The test case comes on planning approvals for building close to powerlines, where a local authority may wish to apply a minimum separation distance in the short term pending further research and advice. It does seem unreasonable that government should prohibit such precaution through appeals and that NRPB should encourage or condone that prohibition.

[1] M J O' Carroll, Parliamentary Brief, p34-36 Jan 96 and p35-36 May 96

[2] M G Morgan, I Nair and H K Florig, Biological effects of power frequency EMFs, US Office of Technology Assessment, 1989

[3] W R Hendee and I C Boteler, The question of health effects from exposure to EMFs, Health Physics 66(2), 127-136, 1994

[4] Radiological Protection Bulletin 151 p3, 154 p15-16 & 155 p14-15, 1994

[5] Lewis Roberts, The public perception of risk, RSA Journal 5464, 52-63, 1995

[6] Microwave News, p12-15, July/August 1995

[7] Sir Austin Bradford Hill, A short textbook of medical statistics, Edward Arnold, 11th edn, 1984

[8] Radiation Protection Bulletin 152 pa, 1994 t9] L-E Paulsson, Electric and magnetic fields from a regulator's point of view, CIGRE paper P4-01, 1996 2

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