About 200 schools and nurseries have been closed in the affected area in southern Johor state after a lorry dumped the waste last week.
People who inhaled the fumes suffered from nausea and vomiting, and a handful were left in critical condition.
The number of those needing medical treatment has been slowly rising since the crisis began and on Friday the figure stood at 2,355, including 113 still in hospital, local lawmaker Sahruddin Jamal told AFP.
No one has died.
Local media have reported the waste was a type of oil commonly used to lubricate ship's engines which emitted methane and benzene fumes. Up to 40 tonnes of the toxic substance is believed to have been tipped into the river.
Three men have been arrested over the dumping of the waste and face up to five years in jail if convicted of breaking environmental protection laws.
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