The daily cup of tea has many positive associations. Winding down (thought to be due to the relaxing presence of amino acid L-theanine), or winding up (thanks to caffeine’s influence).

Along with a dose of ritual comfort, there’s also the health-giving benefits of herbal teas, lauded for antioxidants – the molecules that prevent free radical cell damage – and more.

But recent research has uncovered a connection of a less pleasant kind – the possibility of pesticides and other carcinogenic chemicals in your tea.

Independent lab testing by CBC News Canada has found many tea brands contain pesticides over levels permitted in that country.

CBC’s research found multiple chemicals in eight out of 10 popular brands of green and black tea. Half the teas contained pesticide levels in excess of allowable limits. Tetley, Lipton and Twinings, brands popular with Australians, were among those highest in pesticide contamination.

Indicating more than a random finding, two reports by Greenpeace show pesticides are widely present in leading international tea brands from China and India, the two largest tea-producers in the world.

All 18 brands of Chinese tea tested contained three or more different kinds of pesticides. Six tea brand samples contained up to 10 types of pesticide. One contained 17 types.

Alarmingly, pesticides banned for use on tea by China’s Ministry of Agriculture, were found on 12 of the 18 samples. The teas tested were mid-grade green, oolong and jasmine, and included China’s top tea-sellers.