Angry/sad child
Having high blood lead level was directly linked to anxiety and depression in children.W H/Flickr

Even low exposure to lead, a heavy metal, can cause emotional and behavioral problems in children, a new study says.

Previous research has shown that lead affects the function of every system of the body. While high exposure to the metal can cause convulsions, coma and death; low exposure can result in low intelligence levels in children. Additionally, lead exposure at the early years of growth has also been linked to ADHD (attention deficit hyperactivity disorder) in children and has been found to interfere with students' ability to perform at school.

For the new study, researchers followed 1,300 pre-school children in China. To determine lead exposure, researchers collected blood samples when the children were between three and five years of age. When the children turned six years, parents and teachers completed questionnaires on their behavior.

Though previous studies on the topic have concentrated on health effects of blood lead levels equal to or above 10 micrograms per decilitre, in the current study, lead exposure was defined at lower levels. Kids in the study had an average blood lead levels of 6.4 micrograms per decilitre.

Having high blood lead level was directly linked to anxiety and depression in children.

"This research focused on lower blood lead levels than most other studies and adds more evidence that there is no safe lead level," Dr Kimberly Gray, National Institute of Environmental Health Sciences (NIEHS) Health Scientist Administrator, said in a news release. NIEHS funded the study.

"Young children are particularly vulnerable to the toxic effects of lead, because lead can affect children's developing nerves and brains," senior author of the study, Dr Jianghong Liu, from the University of Pennsylvania School of Nursing, Philadelphia, added.

Citing the risks, in May 2012, experts from the Centers for Disease Control and Prevention (CDC) in the US lowered recommended point of lead level in children from the earlier 10 micrograms per decilitre standard to 5 micrograms. As per the new standards, children above 5 micrograms per decilitre of lead in their blood will be placed under the risk category.

The study has been reported in the journal JAMA Pediatrics.

Though there exists strict rules and regulations regarding the usage and levels of lead in different products, in November last year, Toxics Link, an advocacy group that aims for a toxin-free India, looked at 250 samples of enamel decorative paints available in the Indian market and found that majority of them contained alarming levels of lead.

Lead levels in paints have been a source of concern in other countries also. Identifying the risk associated with using a lead-based paint to paint houses till 1978, the US health authorities later imposed a ban on it.