By Richard Black
BBC science correspondent, in Seattle
US scientists say they have found a link between exposure to lead in the womb and schizophrenia in adulthood.
Lead was widely used in petrol in the 1960s
The discovery is based on a study of blood samples taken from pregnant American women in the 1960s when lead was still widely used in vehicle fuel.
People whose mothers were exposed to high levels of the metal in exhaust fumes were more than twice as likely to develop schizophrenia as adults.
The research was led by Dr Ezra Susser, from Columbia University in New York.
He presented the work to the annual meeting of the American Association for the Advancement of Science in Washington State.
"It's a preliminary finding, but an intriguing one," he told the BBC.
"We think that people will now look at a variety of environmental toxins which can disrupt brain development, and see whether they are also related to the risk of schizophrenia."
Dr Susser believes that lead may interfere with the growth of nerve cells in the baby's brain during a developmental period known as synaptogenesis, when brain cells make many connections to one another.
The suggestion is that cells start to commit suicide when they should not.
He believes lead may operate through the same mechanism which some researchers think gives rise to foetal alcohol syndrome.
In this, a baby's brain is damaged prenatally through the mother's consumption of significant amounts of alcohol.
The search is now on for other samples collected during the era of leaded petrol which could confirm the finding.
If it is confirmed, it would have huge implications for the study of schizophrenia, a condition whose origins have baffled researchers for decades.
Schizophrenia is the most chronic and disabling of the major mental illnesses. It is a highly complex condition, and scientists are not even sure if it is one disorder, or a range of disorders, with different causes.
People with schizophrenia may hear internal voices not heard by others, or believe that other people are reading their minds, controlling their thoughts, or plotting to harm them.
This may make a person with schizophrenia feel anxious and confused. A sufferer may seem distant, detached, or preoccupied. Sometimes they may sit motionless and silent for hours.
Still in use
If lead does disturb early brain development, then scientists will be able to focus on other factors which may do the same thing.
The finding also adds extra weight to the arguments of organisations campaigning to have leaded petrol phased out everywhere in the world.
The dataset used in the research came from the Childhood Health and Development Study which ran between 1959 and 1966 in Oakland and enrolled almost 20,000 mothers.
Dr Susser and his colleague's research is scheduled for publication in a forthcoming edition of the journal Environmental Health Perspectives.
Paul Corry, head of policy and campaigns at Rethink severe mental illness, said: "We welcome any new research or progress into understanding the causes of schizophrenia, but much more research would be needed before it could make a difference to the thousands of people living with severe mental illness in the UK.
"In the meantime, reaching people early with the right care and treatment is the best way of recovering a meaningful and fulfilling life."