U.S. soldiers of the 4th Infantry Division assemble on top of Hill 742, five miles northeast of Dak To, Vietnam, in November 1967. Reuters

An estimated 11.4 million gallons of the chemical pesticide known as Agent Orange were sprayed over millions of acres of Vietnam forests from 1962 to 1970. The United States Department of Veterans Affairs has long acknowledged the link between the substance and diseases like cancer in veterans, but when veterans began reporting having children with birth defects, the VA stayed mostly mum.

But a joint investigation by ProPublica and the Virginian-Pilot published Friday revealed the odds of having a child born with birth defects were found to be a third higher for veterans exposed to Agent Orange than for those who weren’t. The investigation also determined that the VA had collected information about the link between birth defects and Agent Orange during examinations of more than 668,000 veterans but never adequately scrutinized it.

Agent Orange includes a harmful chemical contaminant called dioxin. Production of the herbicide ended in 1970, but it’s estimated that three million Vietnamese people have been affected by it with at least 150,000 children suffering from related birth defects, according to the international non-profit The Aspen Institute.

Members of the U.S. Army's 4th Infantry Division descend the side of Hill 742, located five miles northwest of Dark To, Vietnam, Nov. 1967. Reuters

Agent Orange was sprayed in Vietnam by the U.S. military to destroy forests, shrubbery, and crops used as cover by Vietnamese soldiers.

“It’s like a sign that says, ‘Dig Here’ and they’re not digging,” Dr. David Ozonoff, professor of environmental health at Boston University and co-editor-in-chief of the journal Environmental Health, told ProPublica. “It raises questions about whether they want to know the answer or are just hoping the problem will naturally go away as the veterans die off.”

The reported birth defects included missing limbs and extra limbs, among other diseases.

The VA responded to the investigation by saying the findings were “interesting” and “a step in the right direction,” but said it did not have the resources to adequately study them. The organization urged scientists to analyze them instead.

“VA has recognized certain cancers and other health problems as presumptive diseases associated with exposure to Agent Orange or other herbicides during military service,” the VA website states. “VA presumes certain birth defects in children of Vietnam and Korea Veterans are associated with vterans’ qualifying military service.”

The VA does provide payment to veterans’ children who have spina bifida as well as a limited number of female veterans’ children with a specific set of diseases. Congress also passed a bill last week requiring the VA to pay to an analysis of “all research done on descendants of veterans with toxic exposure."