Polychlorinated biphenyls (PCBs) exposure can increase risk of asthma in children, new research says.

PCBs were widely used until 1970s in inks, paints, lubricants and electrical equipment. These chemicals have been known to increase risk of cancer.

The chemical isn't being used now. However, it is still released from hazardous waste sites, old transformers and improper disposal of some equipment. These chemicals are then washed away in water and stay in the environment for long periods.

Exposure to PCBs is mainly through diet. Children may be exposed to the chemical through breast milk. The chemical takes decades to be cleared from the body.

In the study, researchers from University of Queensland in Australia analyzed levels of PCBs and asthmatic symptoms in 240 children. Their blood was tested for the presence of PCBs and three other pesticides. They found that children who had high levels of PCBs in their blood were most likely to report wheezing (common symptom for asthma).

"Despite PCBs being banned from use in many countries, people are still suffering from the effects of these toxic substances. Our findings suggest that people with high levels of the chemicals in their blood stream are suffering from higher levels of wheeze, a common asthma symptom," said lead author Professor Sly from the University of Queensland in a press release. 

Other studies have found that low levels of PCB exposure can change the way the human brain develops, leading to many learning and behavioral disabilities.

"This could be due to high concentration levels being passed from a mother to a baby while in the womb, or PCBs may be ingested if a person consumes contaminated food. They could also be inhaled from contaminated hazardous waste sites," said Sly.

PCBs were manufactured in Anniston, Alabama in 1971 and have severely contaminated the environment. Studies have shown that the Anniston population is at high risk of developing diabetes.