DANANG, Vietnam — Vo Duoc fights back tears while sharing the news that broke his heart: A few days ago he received test results confirming he and 11 family members have elevated levels of dioxin lingering in their blood.

The family lives in a two-story house near a former U.S. military base in Danang where the defoliant Agent Orange was stored during the Vietnam War, which ended nearly four decades ago. Duoc, 58, sells steel for a living and has diabetes, while his wife battles breast cancer and their daughter has remained childless after suffering repeated miscarriages.

For years, Duoc thought the ailments were unrelated, but after seeing the blood tests he now suspects his family unwittingly ingested dioxin from Agent Orange-contaminated fish, vegetables and well water.

Dioxin, a persistent chemical linked to cancer, birth defects and other disabilities, has seeped into Vietnam's soils and watersheds, creating a lasting war legacy that remains a thorny issue between the former foes. The United States has been slow to respond, but on Thursday the U.S., for the first time, will begin cleaning up dioxin from Agent Orange that was stored at the former military base, now part of Danang's airport.

"It's better late than never that the U.S. government is cleaning up the environment for our children," Duoc said in Danang, surrounded by family members sitting on plastic stools. "They have to do as much as possible and as quickly as possible."

The $43 million project begins as Vietnam and the United States forge closer ties to boost trade and counter China's rising influence in the disputed South China Sea.

Although the countries' economic and military ties are blossoming, progress on addressing the dioxin legacy has been slow.

Washington still disputes a claim by Hanoi that 3 million to 4 million Vietnamese were affected by toxic chemicals sprayed by U.S. planes during the war to eliminate jungle cover for guerrilla fighters, arguing that the actual number is far lower and other environmental factors are to blame for the health issues.

That position irks Vietnamese, who say the United States maintains a double standard in acknowledging the consequences of Agent Orange.

The United States has given billions of dollars in disability payments to American servicemen who developed illnesses associated with dioxin after exposure to the defoliant during the Vietnam War.

In 2004, a group of Vietnamese citizens filed suit in a U.S. court against companies that produced the chemical, but the case was dismissed, and the Supreme Court declined to take it up.

Over the past five years, Congress has appropriated about $49 million for environmental remediation and about $11 million to help people living with disabilities in Vietnam regardless of cause. Experts have identified three former U.S. air bases — in Danang in central Vietnam and the southern locations of Bien Hoa and Phu Cat — as hot spots where Agent Orange was mixed, stored and loaded onto planes.

The U.S. military dumped some 20 million gallons of Agent Orange and other herbicides on about a quarter of former South Vietnam between 1962 and 1971.

The defoliant decimated about 5 million acres of forest — roughly the size of Massachusetts — and another 500,000 acres of crops.

The war ended April 30, 1975.

The country was then reunified under a one-party Communist government. After years of poverty and isolation, Vietnam normalized diplomatic relations with the United States in 1995.