In the early days of cosmic-ray research, rabbits in a normal wooden hutch were compared with rabbits kept down a mine in a lead-lined hutch, to shield them from the rays. The shielded rabbits died faster, suggesting that the rays were beneficial. It later turned out that they had somehow been poisoned by their lead shielding.
Children can likewise be poisoned by lead paint in their homes. One explanation is that they habitually pull flakes of paint off walls and windows, and eat them. But Daedalus recalls that in the nineteenth century, many people (including Napoleon) became poisoned by arsenical wallpaper. They didn't eat the paper: it was colonized by moulds which metabolized the arsenical pigment to volatile arsenic trimethyl. The hapless victims breathed in the liberated vapour. Now lead can also be methylated to a volatile compound — lead tetramethyl, an antiknock agent for petrol. So Daedalus reckons that rabbits and children alike owed their fate to lead tetramethyl evolved from the mouldy walls around them.
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