Chemistry professor says relationship between copper, sodium hydroxide well known

The relationship between sodium hydroxide and copper is well known, says a chemistry professor at Laurentian University.

The interaction of the metal with the chemical is being closely watched by many property owners in Thunder Bay, Ont., after many copper pipes in the city have sprung pinhole leaks.

The city introduced sodium hydroxide into the municipal water supply in 2018 to reduce the amount of lead leaching into the drinking water in homes with lead pipes. The practice was discontinued in 2020 after the city received a number of complaints about pinhole leaks.

"The reaction, I think it's a well known fact that sodium hydroxide is a corrosive material. If you put sodium hydroxide into contact with metal, it will get corroded," said Nelson Belzile, a chemistry professor at Laurentian University.

"It's a very alkaline, a very high pH material in solution."

Belzile said he understands the rationale for using the chemical—it creates a coating on the inside of lead pipes that will reduce the amount of lead entering drinking water.

"This coating is created by a reaction between the sodium hydroxide and the lead material."

He said there are other materials which could be used to achieve the same coating effect, and are not as corrosive as sodium hydroxide.

Those include phosphate, although that substance can have detrimental environmental impacts if used in high quantities, Belzile said. Silica is another substitute, which would also react with lead to create a coating layer of protection inside the pipe.

"The presence of the sodium hydroxide that is creating a problem with the copper pipe, because it is a different material, is not leading to a layer of protection, it is leading to an attack on the copper pipe, and that could create some leaks that have been observed in some locations."

"Other cities have faced the problem, and have tested other materials. They have tested other things that are not necessarily sodium hydroxide, but other compounds that will adjust the pH," said Belzile.

"The question here is adjusting the pH, when the pH is a little more alkaline, not acidic but on the upper side of the scale, you will have this formation of a coating that will prevent, or stop, or at least slow down the release of lead in the water."

Belzile said the best way to eliminate lead in water is to replace all lead pipes, although he does understand the cost involved with pipe replacement. Another option, he said, is to use a water filter which does remove lead.

"It's a question of corrosion. Corrosion, it's a little bit like creating a specific exchange of electrons, of current that will be causing this situation. And, eventually, there will be some leaks, because you attack the copper pipe, and eventually they will start leaking."

The City of Thunder Bay has said it will not publicly comment on pinhole leaks.