High levels of a toxin contained in the harmful haze that is currently blanketing nine upper northern provinces of Thailand have been found in the urine of people who live near areas where burning and forest fires are common.

Chiang Mai University’s Research Institute for Health and Science studied the health impact of haze in the upper northern provinces on residents during the past three years. It found that atmospheric levels of small particles caused by forest and bush fires in areas outside towns were two to three times higher than those in urban areas, depending on weather conditions.

Read more: The Nation