Lead exposure in childhood can turn youngsters into adult criminals

Scientists based the conclusion on two US studies of families from a poor area of Cincinnati where many houses were old and contaminated with lead.

In one, blood lead levels of pregnant women and 250 children born in the early 1980s were matched against information from local criminal justice records.

The researchers found that higher lead concentrations before birth and during early childhood were associated with a greater number of arrests among young men over the age of 18.

Scans showed exposure to lead as a child was linked with brain shrinkage in adulthood

For every 5 microgram per decilitre increase in blood lead at six years of age, the risk of being arrested for violent crime as a young adult rose by almost 50 per cent.

Writing in the journal PLoS Medicine, the team led by Dr Kim Dietrich from the University of Cincinnati, said the findings "implicate early exposure to lead as a risk factor for behaviours leading to criminal arrest".

Although environmental lead levels and crime rates had dropped in the last 30 years, inner city children remained vulnerable to lead exposure, the scientists pointed out.

Dr Dietrich also took part in another study which looked at 157 teenagers aged 15 to 16 who had grown up in lead-contaminated housing.

Scans showed that exposure to lead as a child was linked with brain shrinkage in adulthood, especially among men.

Scientists also say lead exposure can be associated with violent criminal behaviour

The greatest brain volume loss was seen in people with the worst history of lead exposure.

The brain regions involved were those responsible for organising actions, decisions and behaviour, regulating behaviour, and co-ordinating fine movements.

'This analysis suggests that adverse cognitive and behavioural outcomes may be related to lead's effect on brain development producing persistent alterations in structure,' said the researchers in PLoS Medicine.

Dr David Bellinger, an expert from Harvard Medical School in Boston, who was not involved in the research, said: 'Even if the contribution of lead to arrest risk is small, however, it has a special status in that, in contrast to most other known risk factors for criminality, we know full well how to prevent it.'

Impaired IQ, well known to be associated with lead exposure, was "clearly only the tip of the iceberg," Dr Bellinger added.