k„ 14 ards from lead
Dixon
Sed Physicist Ernst Mach is imk h. and revered in countless books .to 1$t°rY of science as the man who Nrge science of metaphysics and !peculation. Behind the wide range ientific work, Mach's constant that scientists should confine to observable, and wherever tr;gieasurable, phenomena. When he '901, Mach left a lasting legacy lit'ss and precision which has had atreverberations throughout the of8tkriences. The "absolute space and diZeWtonian physics, forexample, ; ore "Lnissed as metaphysical and 41.4nleaningless. By insisting that re, tirrie could have meaning only thcee to observable relations bethe made an important step L1-.hstein'5 theory of relativity. 15s3ts, it seems, are slower to learn. Pod example of this defect in the Noned controversy now raging QiIllealth hazards arising from lead 11,4104t\r,ironment. It is now over eigh qi s since Professor Derek Bryce`,_clessor of organic chemistry at a cab., c university, began a vigorous Prlarb;Paign drawing attention to a!of lead pollution. His oneis based on two principal ar
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guments. First, the amounts of lead found in the human body are nearer to the threshold at which poisoning becomes apparent than is the case with any other chemical pollutants. Secondly, it is possible that even below the point where people begin to suffer from obvious toxic symptoms, lead may affect the brain, causing psychological and nervous effects. Bryce-Smith has used these propositions to support his efforts to have anti-knock lead additives removed from petrol — arguably the most important source of lead in our environment. Predictably, both planks of the thesis have been savaged — particularly by critics from the petroleum industry. Yet neither side has produced conclusive evidence. The problem is that we simply can't be certain at what point the amount of lead in our tissues begins to threaten our physical and mental well-being. The characteristics of frank lead poisoning (plumbism) are, of course, well known. (It was the risk of this type of poisoning which led, some years ago, to the introduction of lead-free paints for use on toys.) But what safety margin should there be below the level of intake at which people are in danger of plumbism? This is the crucial question, relevant to both limbs of Bryce-Smith's case. When Rio Tinto-Zinc temporarily closed down its lead and zinc smelter at Avonmouth in April, the company did not do so because workers had succumbed to overt lead poisoning. RTZ acted because some of the men at the plant had quantities of lead in their bloodstream above what was considered the safe maximum. In the absence of decisive data, this safe level' is set on what is thought to be the generous side — the more so because modern analytical techniques now allow biochemists to detect vanishingly tiny quantities of lead.
And yet ... we don't really know. From the outset, Bryce-Smith has emphasised circumstantial evidence (from a number of sources) of correlations between lead intake and vague illness characterised by such commonplace symptoms as depression, fatigue, and headache. Symptoms of this sort are notoriously difficult to assess. (As the neurologist Dr Henry Miller pointed out in a recent medical textbook, most people most of the time will confess to feeling "greatly tired, harassed and under the weather.") Nonetheless, the evidence put forward by Bryce-Smith (who returns to the fray with an article in this month's Chemistry in Britain) is undoubtedly strong enough to merit a full investigation to settle the matter conclusively.
Hence to the message of Ernst Mach. Comparing the incidence of vague psychological symptoms in groups of people exposed to different levels of environmental lead may be difficult, but it could be done. Reliable, sophisticated psychological tests have been devised to pinpoint such ill-defined symptoms. They have been successfully used recently to reveal latent poisoning among industrial workers exposed to a particular chemical solvent, carbon disulphide. As a chemist, it is not in Bryce-Smith's province to conduct such tests himself. But we now know that they are feasible. It would be a welcome change from the present emotional flavour of the environmental lead debate if someone would initiate the necessary research — and quickly.
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