Workers exposed to pesticides and herbicides on the job may be more likely than other people to develop chronic obstructive pulmonary disease (COPD), bronchitis and other breathing problems, an Australian study suggests.

With any herbicide exposure at work, people were more than twice as likely to develop COPD by middle age, and workplace pesticide exposure was associated with 74% higher odds of the common lung disease, researchers report in Thorax.

Over a lifetime, pesticides and herbicides may pose an even bigger added risk for breathing disorders, the study also found.

Each ten-year increase in occupational exposure to pesticides carried a 12% increased risk of COPD and a 16% higher risk of developing chronic bronchitis. Every extra decade of herbicide exposure, meanwhile, carried a 22% increased risk of bronchitis, while each ten years of insecticide exposure was associated with 15% higher odds of bronchitis.

“Our study looked at long-term exposure to pesticides, and it is thought that long-term exposure to pesticides increases mucus secretion and muscle contraction in the lungs, causing breathlessness, cough and wheeze,” lead study author Dr Sheikh Alif of the University of Melbourne in Australia said by e-mail.

Globally, more than 65mn people have moderate to severe COPD, and the condition causes about 5% of all deaths, according to the World Health Organisation (WHO).

Most cases are caused by smoking or exposure to second-hand smoke, but working or cooking around certain toxic dusts, chemicals and fuels can also contribute, as can frequent respiratory infections during childhood.

For the current study, researchers examined data collected on 1,335 workers from 2002 to 2008, including information on workplace exposure to pollutants as well as results from breathing tests to detect COPD and other respiratory issues.

Study participants were 45 year old on average, 87% were currently employed and 25% were current smokers.

Overall, 6% of them had COPD, 8.6% had chronic bronchitis, and more than 28% reported having asthma currently or previously.

In addition to risks associated with pesticides and herbicides, the study also found workers who didn’t have asthma had an increased risk of COPD when they had any exposure to toxic mineral dust, gases, fumes and vapors. There didn’t appear to be an association between exposure to these pollutants and COPD in people with asthma, however.

The study wasn’t a controlled experiment designed to prove whether or how exposure to pollutants at work might contribute to COPD, bronchitis or other breathing problems.

“We cannot make firm conclusions about the extent of exposure needed to cause changes in lung function,” said Dr Steve Georas, an environmental health researcher at the University of Rochester in New York who wasn’t involved in the study.

“We know that single exposures to high levels of some toxicants can cause long lasting changes in airway function (ie chlorine gas),” Georas said by e-mail. “I suspect that for pesticides and herbicides, long-term low level exposure may be more important, but this is speculation.”