In June, construction workers unearthed more than 20 rusty barrels from beneath a soccer pitch in Okinawa City. The land had once been part of Kadena Air Base — the Pentagon’s largest installation in the Pacific region — but was returned to civilian usage in 1987. Tests revealed that the barrels contained two ingredients of military defoliants used in the Vietnam War: the herbicide 2,4,5-T and 2,3,7,8,-TCDD dioxin. Levels of the highly toxic TCDD in nearby water measured 280 times the safe limit.

The Pentagon has repeatedly denied storing of defoliants — including Agent Orange — on Okinawa. Following the discovery, it distanced itself from the barrels; a spokesperson said the Defense Department was investigating whether they had been buried after the land’s return in 1987, and a U.S. government-sponsored scientist suggested they may merely have contained kitchen or medical waste. However, the conclusions of the Japanese and international scientific community were unequivocal: Not only did the barrels disprove Pentagon denials of the presence of military defoliants in Japan, but the polluted land also posed a threat to the health of local residents and required immediate remediation.

The Pentagon is the largest polluter on the planet, producing more toxic waste than the top three U.S. chemical manufacturers combined. In 2008, 25,000 of its properties within the U.S. were found to be contaminated, and more than 100 of these were classified by the Environmental Protection Agency as Superfund sites, meaning they warranted urgent cleanup.

Although Okinawa’s main island hosts more than 30 U.S. bases — taking up 20 percent of its land — there has never been a concerted attempt to investigate levels of contamination within them. Unlike other nations with U.S. bases, such as South Korea and Germany, the Japanese government has no effective powers to conduct environmental checks; nor does the Pentagon have a duty to disclose to the public any contamination that it knows exists. To date, most incidents of pollution have only become known when individual service members have divulged details to the media or, as in the case of the barrels uncovered in Okinawa City, the Japanese authorities have conducted tests following the return of military land.

Despite their limited scope, such disclosures offer a disturbing window into the contamination of Okinawa. Over the past seven decades, the island’s sea, land and air have been contaminated with toxins including arsenic, depleted uranium, nerve gas and carcinogenic hexavalent chromium. These substances have poisoned Okinawan civilians and U.S. troops alike — and it is highly probable that they are damaging the health of those living on the island today. But, regardless of these risks, the Pentagon continues to do everything it can to evade responsibility for the damage its bases cause.

The history of U.S. pollution on Okinawa is almost as long as its ongoing military presence. Following the end of World War II, Okinawa earned the nickname the “junk heap of the Pacific” due to the large volume of surplus supplies abandoned there. During this period, one of the first known instances of contamination occurred when eight residents of Iheya village were killed by arsenic poisoning from a nearby U.S. compound in 1947.

The 1952 Treaty of San Francisco granted the Pentagon full control of Okinawa and, as the military seized large tracts of civilian land to convert into bases, the dangers of pollution grew. Fuel leaks saturated the ground, industrial-grade detergents flowed from runways into nearby streams and solvents were flushed away without any regard to where they ended up.

Although such lax environmental controls were common on U.S. military bases all over the world at this time, Okinawa’s problems were exacerbated by the geopolitical gray zone in which it existed. Throughout the 1945-1972 U.S. occupation, the island was not protected by American law or the Japanese Constitution, so the Pentagon stored large stockpiles of chemical and atomic weapons there — and nuclear-powered submarines made regular pit stops in Okinawa.

In September 1968, Japanese newspapers reported that radioactive cobalt-60 had been detected in Naha Port — believed by scientists to have emanated from visiting U.S. subs. Three Okinawan divers claimed to have been sickened by their exposure to the substance, which accumulated in mud at the bottom of the harbor.

The next year, the Wall Street Journal broke the news of a leak of nerve gas at Chibana Ammunition Depot, near Kadena Air Base, that hospitalized more than 20 U.S. service members. Precise details of the subsequent mop-up operation remained hidden until July this year, when U.S. veterans stationed on the island at the time described how tons of the chemical munitions had been dumped off Okinawa’s coast. Experts estimate that the metal containers holding these poisons corrode after 50 years, threatening the health of fishing crews and coastal communities today.

During the Vietnam War, Okinawa served as the Pentagon’s primary staging post for the conflict. Led by the U.S. Army’s 2nd Logistics Division, the military channeled the majority of its supplies — including ammunition, coffins and, it now seems, Agent Orange — via the island’s ports. This transportation was a two-way street: Surplus and damaged materiel was also returned from the war zone to Okinawa for reprocessing.

In 1969, U.S. Army Chemical Corps 2nd Lt. Lindsay Peterson was the officer in charge of these retrograde supplies at Hamby Open Storage Area, central Okinawa. In a recent interview with The Japan Times, he recalled how damaged barrels of Agent Orange were among chemicals shipped to the island.

“Agent Orange was processed through the port at Naha and trucked to the Hamby Open Storage Area,” he said. “When I arrived, there were around 10,000 barrels. Most of them were leaking, so we had to empty them into new 55-gallon [208-liter] drums.”

Peterson recalls how the re-drumming process saturated his crew with defoliants. He is among hundreds of seriously ill U.S. veterans who believe their sicknesses were caused by exposure to dioxin-tainted defoliants while serving on Okinawa. Although the U.S. government has refused to help the majority of these veterans, in 2008 it awarded compensation to a former marine warehouseman suffering from Hodgkin’s lymphoma and type-2 diabetes sparked by handling Agent Orange-contaminated supplies brought back to Okinawa from the Vietnam War in the early 1970s.

Other U.S. veterans and Okinawa civilians interviewed by The Japan Times recall how surplus stocks of Agent Orange were sold on the black market to local farmers who valued its potent weed-killing power. The risks of the unregulated sale of hazardous substances to those lacking the necessary safety training became clear in 1971 when large volumes of pentachlorophenol herbicides — obtained from the U.S. military by a civilian company — were dumped in the Haebaru and Gushikami districts of southern Okinawa. The chemicals leaked into Kokuba River and the water supply to 30,000 people had to be halted; children attending local schools suffered from abdominal pains and nausea.

U.S. government correspondence obtained by The Japan Times reveals the reaction of the authorities to such pollution during this period. In August 1975, following a leak of detergents containing poisonous hexavalent chromium at Machinato Service Area, the U.S. consulate in Naha sent a series of updates to the State Department in Washington. Dismissing the spill as a “flap,” it concluded that “the newspapers and the leftists will certainly make good use of this issue against us.”

In September 1974, the U.S. Consulate had displayed a similar tone when Okinawa Gov. Chobyo Yara voiced his fears to the U.S. military that its aging oil pipelines might leak. In a cable, the U.S. Consulate in Naha brushed off the governor’s concerns, noting the “pipeline has now been added to leftist catalogue of evils of U.S. base system.” A little over a year later, in January 1976, Yara’s concerns were proven justified when one of the pipelines spilled 14,000 gallons (53,000 liters) of diesel into a local river.

In the 1970s, the Pentagon showed more concern over potential PR damage than the risk to human health; today, its stance toward the discovery of the dioxin-contaminated barrels in Okinawa City seems identical. Its denials attempt to protect its image of a good neighbor — but in reality, they potentially sacrifice the health of local Okinawans, its own service members and their dependents. Although the Okinawa City dioxin site is located adjacent to two Department of Defense schools, it appears that the parents and teachers there have not been informed.

During the 1970s, such neglect could have been blamed on a lack of environmental awareness. However, today in 2013, such a posture is criminal — reminiscent of the contamination of Camp Lejeune, North Carolina, where tens of thousands of troops and family members were exposed to toxins including pesticides, benzene and industrial solvents between 1953 and 1987.

The Status of Forces Agreement (SOFA) — the foundation, unchanged since 1960, that spells out the rights and role of the U.S. military in Japan — encourages the Pentagon’s cavalier approach to pollution. SOFA absolves the U.S. of all financial responsibility for cleaning up land it has contaminated and does not allow the Japanese authorities to conduct spot-checks on U.S. military bases.

Given these constraints on access to U.S. installations, Japanese scientists have been forced to improvise. Recently, experts from Ehime and Meio universities conducted tests on seven mongooses whose habitat included U.S. bases. Announced in August, the results showed the animals were contaminated with high levels of polychlorinated biphenyls (PCBs) — raising worries that humans living in the same areas may be poisoned, too.

Mongooses aside, the only alternative has been to conduct tests on military land following its return to civilian control. As in the case of Okinawa City, such checks often reveal dangerous levels of contamination. In Yomitan village, for example, levels of arsenic 120 times over the legal limit were found on former U.S.-controlled land in 2008. In July this year, asbestos was discovered at a site that used to be a part of Camp Courtney. In this case, the U.S. authorities appear to have misled the civilian construction company tasked with the cleanup — leading to the suspected exposure of Okinawan workers.

But even after pollution has been detected, the new problem arises of how to deal with it. In September it was revealed that 322 tons of PCB-laden slurry from former U.S. military land in Okinawa was to be shipped for disposal to Iwaki city, Fukushima Prefecture — a municipality located 50 km from the stricken No. 1 nuclear power station. Critics of the plan accused the Japanese authorities of exploiting the prefecture’s need for money and worsening its already dire pollution problems.

In the coming years, it is likely such troubles will become more pressing. In October, Japan’s minister of defense, Itsunori Onodera, reiterated plans to concentrate the U.S. military presence in the northern half of Okinawa Island — a move that will entail the closure of several installations including Machinato Service Area, one of the main bases where defoliants were allegedly stored, and, ultimately, Marine Corps Air Station Futenma. Experts have estimated the cleanup of Futenma at $600 million — but that was before the cost of Agent Orange remediation had been figured into calculations.

Okinawa residents have long protested for a future with fewer bases. But even after their wish becomes a reality, it seems the land they’ve fought so hard to retrieve will be uninhabitable for years — if not decades — to come.

U.S. military pollution in Okinawa: a timeline

1947: Arsenic contamination at base on Iheya Island kills eight Okinawans.

1968: Cobalt-60 leaks from nuclear-powered submarine visiting Naha Port.

1969: More than 20 U.S. service members sickened by nerve gas at Chibana Ammunition Depot; following the accident, tons of chemical weapons allegedly dumped off Okinawa’s coast

1971: Surplus U.S. herbicides containing pentachlorophenol contaminate civilian water supplies in Haebaru and Gushikami districts.

1975: Large leak of hexavalent chromium at Machinato Service Area; contamination reportedly some 8,000 times safe standards.

1975: Spill of Vietnam War retrograde chemicals (including herbicides and pesticides) kills sea life near Camp Kinser.

1976: More than 50,000 liters of fuel leak into stream near Camp Foster.

1981: U.S. Marines unearth cache of over 100 barrels (some suspected of containing Agent Orange) at Marine Corps Air Station Futenma; top officers apparently hush up the incident.

1995/96: Iwakuni-based U.S. Marine jets fire more than 1,500 shells of depleted uranium at and around Torishima island; area subsequently declared off-limits due to radiation fears.

1996: Land returned to civilian usage on former Onna Communication Site found to contain dangerous levels of mercury, cadmium and polychlorinated biphenyls (PCBs).

2000: Japan attempts to ship overseas 100 tons of PCBs from U.S. bases; vessel blocked from entry to Canada under international laws banning export of toxic waste.

2002: Over 200 barrels containing unidentified tar-like substance unearthed on former military land in Chatan Town.

2003: High levels of lead and hexavalent chromium discovered on land in Chatan Town that was previously part of Camp Kuwae.

2007: Almost 9,000 liters of jet fuel leak on Kadena Air Base.

2013: More than 20 barrels of suspected Vietnam War defoliants unearthed on soccer pitch in Okinawa City; authorities begin to search field for more buried barrels.