The Pentagon needs to study the long-term health effects of exposure to the chemicals inhaled from burn pits at its overseas military bases, the Government Accountability Office says in a report.

While the report, released in September, credited the Department of Defense with improving practices to mitigate the risks of exposure to the burn pits, the department still needs to ensure that “research specifically examines the relationship between direct burn pit exposure and long-term health issues.”

The GAO found there hasn’t been enough progress on this issue over the past five years, when it first said more study was needed.

“The current lack of data on emissions specific to burn pits and related individual exposures limits efforts to characterize potential long-term health impacts on service members and other base personnel,” the report warned.

Open-air burning has always been a mainstay of waste disposal during times of war. But the technology of modern warfare means that such new items as plastic bottles and electronics are being burned, presenting new health risks.

Burn pits were constructed at more than 230 U.S. military bases across Iraq and Afghanistan before their use was restricted in 2009. Although the military gave assurances that the air quality was within safe levels, troops returning home began complaining of problems as early as 2004.

Massive open-air burn pits at the bases billowed the toxic smoke and ash of everything from Styrofoam, metals and plastics to electrical equipment and even human body parts.

The flames were stoked with jet fuel.

While it took nearly three decades for the U.S. government to eventually link Agent Orange, the defoliant used in Vietnam, to cancer, President Obama has pledged quick action to make determinations about the effect of the burn pits on perhaps as many as 60,000 U.S. troops.

A 2011 report by the Institute of Medicine outlined the data needed for assessing exposures and potential related health risks. In response, the Department of Veterans Affairs established a registry to collect information. However, the Department of Defense has not undertaken data-gathering and research efforts to specifically examine this relationship to fully understand any associated health risks, the GAO report said.

To date, the VA’s official position is that research has not established evidence of long-term health problems from exposure to burn pits. The magnitude of the issue, however, may not be clear for decades as delayed war ­casualties slowly emerge. In Minnesota alone, it is estimated that more than 14,000 Minnesota Army and Air Guard troops qualify to be part of a national registry for potential burn pit exposure, based on where they were stationed during deployments.

The Star Tribune recently documented the plight of Minnesota Air National Guard veteran Amie Muller, who is battling pancreatic cancer and several other maladies after returning from deployments to Balad Air Base in Iraq, site of one of the most notorious military base burn pits.

Despite the mounting public outcry from vets, their families and members of Congress, the VA continues to say research does not show evidence of long-term health problems, and that most irritation is likely temporary. U.S. Sen. Amy Klobuchar has proposed a national center to study the long-term affects of burn pits.

While generally agreeing with the GAO report, the Pentagon said the report should have acknowledged research that the Department of Defense already has completed with other organizations.