LEAD has proved to be such a useful, malleable metal that it turns up everywhere, from water pipes to window flashing and printing type. It went into car batteries, and into additives that gave petrol more vroom. It also helped make bright pigments, used to paint walls, metalwork and toys.

Yet lead is also a poison, and its ubiquity makes it a pernicious one (see article). In the worst cases it causes comas, convulsions and death. More often it acts insidiously. It is a menace to toddlers, who are most likely to ingest contaminated dust and paint chips. Their brains are especially vulnerable. Only years after exposure are the results apparent in lower IQs, behavioural disorders and learning disabilities.

The dangers of lead have long been known. America banned it from paint 40 years ago, and by the late 1990s leaded petrol had been phased out in almost all rich countries. But the effects linger. Half a million American children are diagnosed with lead poisoning. The situation is more alarming in the poor world, where the use of lead-based paints is spreading. Curbing lead poisoning more than pays for itself. There is little excuse for poor countries to repeat the mistakes of rich ones.

The Romans did themselves no good by using lead for water pipes and sometimes even as a food sweetener. In 1786 Benjamin Franklin wrote a letter to a friend noting how the use of lead in distilleries had caused North Carolina to complain against New England Rum “that it poison’d their People, giving them the Dry Bellyach, with a Loss of the Use of their Limbs.”

In 2015 the Institute for Health Metrics and Evaluation, a research institute in Seattle, estimated that exposure to lead globally caused about 500,000 deaths that year and 12% of developmental disabilities, such as cerebral palsy and epilepsy. Another estimate is that lead poisoning costs Africa $135bn a year in lost output, the equivalent of 4% of GDP.

The most urgent task is to stop putting more lead into the environment. As people in Asia and Africa become richer, they start to spruce up their homes. But the paint they use, even from pots labelled “lead-free”, often contains it. And they lack facilities to recycle lead batteries properly.

It is neither difficult nor expensive to stop using lead. All countries should ban lead in paint. There should be no exemptions for industrial use, because the contamination spreads and industrial paint inevitably finds its way into the consumer market. Yet only four sub-Saharan African countries have formally enacted bans and local manufacturers are often unaware of the harm that lead causes.

The next step is to find and remove more of the lead introduced decades ago, particularly in rich countries. This will not be cheap, especially when the clean-up involves replacing lead pipes, as it often does in America. But the costs are worth it. The Pew Charitable Trusts, an NGO, reckons that every dollar spent on “lead abatement”—painting over old painted walls or removing flaking woodwork—saves at least $17 in medical and special-education costs, and lost productivity.

In America investigations are typically carried out only in known cases of lead poisoning. However, children should not be used to test dangerous living conditions. It would be better to test older houses before problems appear.

Cities and states need to make sure that landlords carry out remedial work. When poor owners cannot afford to fix their homes, the government should help as a prophylactic to save money on health care and education later. Charities that seek to help sick children and poor countries can contribute, too. There is no need to poison so many young minds.