大象传媒

For thousands of years the aristolochia plant with its reddish-yellow flowers has been a mainstay of Chinese herbal medicine. Sometimes referred to as birthwort in Europe, the toxic nature of the plant was discovered in the 1990s when dozens of Belgian women began developing kidney failure and urinary tract cancers. They had been using aristolochia-based slimming aids at clinic.

Now scientists say that the key element, aristolochic acid, is responsible for the very high levels of kidney disease and urinary tract tumours in Taiwan. It's estimated that about one in three of the population there have used herbal medicines containing the toxin. The country has the world's highest incidence of cancers of the upper urinary tract - and in their study the scientists say more than half can be directly linked to the ingredient.

While products containing aristolochic acid are banned in many countries, one of the big concerns is China. In 2004 a study suggests Chinese farmers produce enough of the plant to dose 100 million people. Scientists are concerned that in the decades to come, disease caused by the aristolochia will create an international public health problem of considerable magnitude.