There's more news out there hinting at the possible toxic impact of second-hand smoke on children.

A report in the latest issue of Pediatrics finds that the rate of ADHD, other developmental disabilities and conduct/behavioral disorders is significantly higher among children raised in homes where people smoke cigarettes.

Although the epidemiological study offers no evidence of causation, it finds a notable correlation. In homes with cigarette-smokers, children have a 50 percent greater rate of developing at least two of those conditions than do children in smoke-free homes.

According to the study, done by researchers from the Harvard School of Public Health, homes with smokers are associated with about 274,000 additional caes of ADHD, other learning disabilities and/or behavioral/conduct disorder in the U.S.

Second-hand smoke has been proven clearly harmful to the health of children. It's well-established that it contributes to sudden infant death syndrome, lower respiratory infections, middle-ear disease, more-severe asthma, respiratory symptoms and slowed lung growth.

Further studies into the relationship between passive smoking and neuro-behavioral disorders, especially if they show that passive smoking contributes to the development of such disorders, will raise the question of how the health-care and child-protection systems should respond. While it doesn't rise to the level of child abuse or neglect as generally defined by law, creating a toxic environment in the home hikes the odds of a child's developing one of a raft of illnesses and disabilities.

If researchers find more evidence linking passive smoking to the development of neuro-developmental disorders, and if the evidence shows causation, rather than mere association, policy makers may have to address the contentious issue of how to protect children from such toxic exposures.