Chemical extracts from cigarette butts - so toxic they kill fish - can be used to protect steel pipes from rusting, a study in China has found.

In a paper published in the American Chemical Society's bi-weekly journal Industrial and Engineering Chemistry Research, the scientists in China said they identified nine chemicals after immersing cigarette butts in water.

They applied the extracts to N80, a type of steel used in oil pipes, and found that they protected the steel from rusting.

"The metal surface can be protected and the iron atom's further dissolution can be prevented," they wrote.

The chemicals, including nicotine, appear to be responsible for this anti-corrosion effect, they added.

The research was led by Jun Zhao at Xi'an Jiaotong University's School of Energy and Power Engineering and funded by China's state oil firm China National Petroleum Corporation.

Corrosion of steel pipes used by the oil industry costs oil producers millions of dollars annually to repair or replace.

According to the paper, 4.5 trillion cigarette butts find their way into the environment each year. Apart from being an eyesore, they contain toxins that can kill fish