A new study from researchers at the Nanjing University in China and the Hong Kong University of Science and Technology found that cooking with chloraminated tap water and iodized table salt can produce harmful toxins in food. To disinfect the water, facilities add chlorine (chlorination) or chloramines (chloramination), if ammonia is added, too. These processes affect the water's chemical make-up.

When iodized table salt is added to tap water containing chloramines or chlorine during cooking, it reacts and creates hypoiodous acid. When this acid reacts to other organic matters in the tap water and food, it creates iodinated disinfection byproducts (I-DBPs). Some of these molecules have not been discovered yet and are completely new to engineers, toxicologists and environmental chemists. In the study, the researchers tested the toxicity of the molecules by simulating the cooking process and adding iodized salt and wheat flour to the various types of tap water heated at various lengths and temperatures.

The team identified 14 new molecules, nine of which got toxicity level test, and found that several of them are 50 to 200 times more toxic compared to others. The presence of molecules during the simulated cooking ranged between 0.72 to 7.63 micrograms per liter.

"Considering that these molecules could have an adverse effect on our health, we need to study them more to determine exactly what effects they might have," said study author and Nanjing University assistant professor Dr. Yang Pan.

The research team suggested that reducing the time and changing the type of salt and water used in cooking can limit the formation of molecules. Using chlorinated tap water instead of chloraminated tap water can also limit the formations, added associate professor and co-author Dr. Xiangru Zhang from the Hong Kong University of Science and Technology. Switching to potassium iodate-fortified table salt, cooking at lower temperature and reducing cooking time can also reduce I-DBP formation.

Zhang added that the discovery is relevant not just researchers who study drinking water, but also to the general public. If people are worried about the quality of water they drink every day, they should also worry about the quality of water we use for cooking.

The study was published in the Water Research journal.