Spokesman Richard Deane says the solution likely contained sodium hydroxide which the plant uses to de-mineralize feed water for the smelter's boilers.
Sodium hydroxide is in an industrial cleaning agent also known as lye or caustic soda and can cause severe skin burns and eye damage.
Deane could not say if a harmful amount of the chemical was drained into the river.
Deane says the solution was accidentally drained to a domestic sewage plant leading to the river instead of getting treated.
B.C.-based Teck Resources is facing a class-action lawsuit in the United States on allegations unrelated to this spill that its smelter in Trail has polluted the Columbia River.
A woman from Washington state says pollutants released into the water as recently as March 2011 are to blame for her breast cancer and other health problems.
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