PUTRAJAYA - The airborne pollution that has affected dozens of students in Johor's Pasir Gudang district were caused by leftover chemical waste in Sungai Kim Kim that was supposed to have been cleaned up three months ago, Malaysia's Housing and Local Government Minister Zuraida Kamaruddin said on Monday (June 24).

She said initial investigations found the cleaning contractor assigned to clear the waste did not do a thorough job in clearing the hazardous materials, Bernama news agency quoted her as saying.

"As the hazardous materials have been exposed to wind and rain, the uncontrolled air borne substances may have spread and affected the people once again," she told reporters in Putrajaya, the news agency said.

The minister said she conclusions were based on initial investigations by the fire department which is under her ministry.

Ms Zuraida said the Department of Environment and the Johor state government have been informed of the development to ensure that the items are disposed of properly.

"We have confirmed that this was the remnants of chemical substances which had previously polluted Sungai Kim Kim," she was quoted as saying by New Straits Times on its website on Monday.

In March, 111 schools in the Pasir Gudang district were shut for two weeks following chemical pollution of Sungai Kim Kim.

The dumping of chemical substances on March 7 caused 5,848 people to seek medical treatment after inhaling toxic fumes from the river.

Several men from a used tyre processing factory were charged at the Johor Baru court in March with 15 offences under two environmental regulations.

In the last incident, all kindergartens, schools and institutions of higher learning in the Taman Mawar area of Pasir Gudang were ordered to close until Thursday as more students suffer from breathing difficulties and vomiting.

More than 70 people including many students have sought treatment after being exposed to toxic fumes, according to The Star newspaper. The symptoms included breathing difficulty and vomiting.