The world’s oldest documented plutonium contamination may not lie in the Chihuahuan Desert at the Trinity Site, where the first-ever atomic bomb ripped open the skies and melted the sand into green glass. Rather, that distinction more likely goes to Los Alamos’s Acid Canyon, according to an independent study by Michael Ketterer, professor emeritus of chemistry and biochemistry at Northern Arizona University.

Ketterer announced these findings at an online press conference held by Nuclear Watch New Mexico on Aug. 15, after collecting and analyzing soil, water and plant samples in Acid Canyon, a popular hiking area in the middle of town. Beginning in 1943, the year the Manhattan Project came to Los Alamos, workers released radioactive waste into the canyon. Three remediations would follow, but as Ketterer’s analysis found, “a super weapons-grade” plutonium persists in the soil, water and plant life in and around Los Alamos, representing some of the earliest ever made.

One thought came to his mind as he analyzed samples from the area, collected last month: “I’ve never seen anything like this in any samples anywhere,” he told Searchlight New Mexico in an interview. 

Scientists in the niche community of nuclear forensics can identify the point of origin of a particular nuclear material based on its composition of isotopes, a process called fingerprinting. Ketterer believes his findings prove unequivocally that legacy plutonium from Los Alamos National Laboratory has not only remained in Acid Canyon all these years later, but also migrated beyond, even after the cleanups. “It’s just a ribbon of contamination going down to the Rio,” he said.

Using a technology called mass spectrometry, Ketterer said this scenario became apparent after he found that several samples from scattered sites in Acid Canyon — whose trailhead is tucked behind the Los Alamos County Aquatic Center — had the same fingerprint, one that dated to the earliest days of the Manhattan Project. He realized just how far that plutonium had traveled when he also collected the identical fingerprint in Los Alamos Canyon, some 12 miles southeast of Acid Canyon, near the Phillips 66 gas station in Totavi — washed downhill by monsoon rains.

The contaminants’ ultimate destination, he wrote in his brief report, is the Rio Grande, where plutonium has already been detected. His results confirm the findings of a 2024 study by Nuclear Watch New Mexico that used data culled from LANL’s online database, Intellus New Mexico, to map plutonium contamination around Los Alamos.

The results of Ketterer’s study stemmed from samples he collected on two occasions in July — including surface water from Acid Canyon and soil and vegetation from Acid and Los Alamos Canyons — all analyzed at the Trace Element Analysis Center at Northern Arizona University in Flagstaff, one of approximately half-a-dozen academic labs of its kind in the nation.

New Mexico does not have a statutory limit for plutonium contamination in soil. Nor does the state have a standard that caps how much plutonium is allowed in surface waters like the Rio Grande. Instead, plutonium is regulated by the federal Department of Energy, as a result of the Atomic Energy Act of 1954. (Other elements such as uranium or radium are regulated by the state’s Water Quality Control Commission.)

Colorado, by contrast, has a state standard for plutonium in both ground and surface water. If applied in New Mexico, the highest reading from Ketterer’s water samples — taken from an intermittent stream in Acid Canyon — would be 573 times higher than Colorado’s limit of 0.15 picocuries of plutonium per liter of water.

Los Alamos County, which owns Acid Canyon, declined to respond to Searchlight’s request for comment.  

The U.S. Department of Energy said it regularly monitors the area for contamination.

“The safety of the public, the workforce and the environment remain DOE’s top priority,” spokesperson Patrick Hefflinger said in an email to Searchlight New Mexico. “We have comprehensive sampling and monitoring programs and a dedicated legacy cleanup program that is addressing the Manhattan Project and Cold War-era legacy contamination across the DOE complex.”

Rocky Flats standard exceeded

The plutonium Ketterer found in the soil, despite the cleanups, does exceed one of the few comparable measures for plutonium levels that remain after remediation — 50 picocuries per gram, the allowed limit for the cleanup of Rocky Flats. Almost four decades ago, the FBI shut down the Cold War-era plutonium-pit factory for environmental crimes, among them the release of radioactive contaminants into nearby waterways. Today, it’s a Superfund site fenced off to the public and buffered by a wildlife refuge.  

The Rocky Flats standard is not without its own criticism, though. “Fifty picocuries of plutonium per gram of soil is something many of us argue is not a safe level in terms of public health,” said Deborah Segaloff, professor emeritus of molecular physiology and biophysics at the University of Iowa. Segaloff now lives in Colorado and serves as a board member of the state’s chapter of Physicians for Social Responsibility.

Ketterer’s most contaminated soil sample had 78 picocuries per gram of plutonium.

“I would be concerned for my safety and the safety of others given the levels he reported,” Segaloff added, after consulting Ketterer’s report. The type of radiation that plutonium emits does not travel far or even penetrate the skin, she said, but if inhaled or ingested, “it will emit radiation to surrounding cells” in the human body, potentially “giving rise to cancer initiation and growth,” the effects of which “may not be obvious until years or decades after exposure.”

At least two studies by the federal government, however, have concluded that there is little risk to people visiting the canyon.

In 2000, when LANL estimated the potential health risks from plutonium exposure in the area, it determined that, as is — without any cleanup — the radionuclides in the canyon’s sediments posed “no unacceptable radiation dose to recreational users of the South Fork of Acid Canyon.” 

The lab further estimated in a 2018 report that a “recreationist” in Acid Canyon would receive between .009 and .022 millirem of radiation, a tiny fraction of what’s allowable. The DOE’s annual limit for minors and the general public, for instance, is 100 millirem. 

Soil, water and plant life are part of the same interconnected ecosystem. Contamination found in water, in other words, could point to the need for more remediation in the soil. In fact, the Institute for Energy and Environmental Research, a nonprofit dedicated to making scientific information available to the public, made that recommendation to the DOE in 2005. Once the DOE assessed the impact of plutonium in surface water, the IEER report read, “significant additional remediation of the South Fork of Acid Canyon will likely be required.”  

The risks are manifold, Ketterer and other advocates believe: If there is a wildfire in the canyon, the plutonium held in the roots of contaminated plant life could go into the air; contaminated surface water, under the right conditions, could contaminate the aquifer; and people hiking in the canyon could be exposed to plutonium-laced sediment, said Segaloff. She added that even a windy day could kick up tiny radioactive particles in the soil.

“It’s been there for 80 years,” Ketterer said. “It’s not marked, it’s accessible to the public, it’s close to people’s houses, and there’s levels in the canyon sediments that should have been remediated.” 

Three cleanups 

Acid Canyon carves a tentacle-like cleft off the western side of the Pajarito Plateau, itself formed from two of the Valles Caldera’s ancient eruptions. The Los Alamos Ranch School established a hiking trail in the canyon decades before scientists’ secret arrival on the hill in 1943. Within months, workers from the Manhattan Project began to dump liquid wastes in the area, laden with strontium, cesium, uranium, americium, tritium and plutonium.

While the practice of sending raw radioactive waste into the canyon ended in 1951, the lab continued to release its treated waste there until 1964. Three years later, the Atomic Energy Commission deeded Acid Canyon to Los Alamos County. The presence of plutonium was never mentioned in the deed.

Some remediation took place between 1966 and 1967, and backhoes scraped up Acid Canyon’s hottest hot spots in 1982 — removing up to eight inches of sandstone and volcanic rock from the canyon floors, a cleanup report stated. The canyon was already “used for recreational activities,” the report went on, and it was “conceivable” that developers would someday build homes and storefronts in the area. At the time, the DOE claimed that the site’s cleanup complied with standards that protected human health and the environment. 

But in 2001, the DOE embarked on yet another remediation, removing some 500 tons of soil ​​around the same time that the lab authored several internal reports noting that plutonium did indeed travel offsite. “Particles carried by floods can be transported long distances from the source and redeposited in the channel or on adjacent floodplains,” one report noted. Contaminants from Acid Canyon, it further added, had traveled at least 12 miles away.

Another report mentioned that storm flows increased after the Cerro Grande Fire in 2000, which also increased the “concentration and transport of radionuclides, particularly plutonium-239 and plutonium-240, in stormwater runoff and sediments.” In 1999, still another report acknowledged that LANL’s plutonium had reached Cochiti Lake. 

After concerns that the lab’s “legacy discharges” — releases dating back to the Manhattan Project and Cold War — could threaten the public water supply around the Rio Grande Basin, New Mexico’s Water Quality Control Commission “adopted monitoring and disclosure criteria” in 2010, according to New Mexico Environment Department spokesperson Jorge Estrada.

Monitoring and disclosure, however, do not amount to regulation or remediation, environmental advocates noted.

The lab is currently prioritizing a new wave of plutonium pit production over remediation of its legacy waste sites, said Jay Coghlan in the Aug. 15 press briefing. “As a matter of percentage, cleanup is running at about five percent of [LANL’s] total institutional budget, whereas the budget for core nuclear weapons and production is around 79 percent.” 

Long experience, 50,000 samples

Over an almost 25-year career, Ketterer has amassed and analyzed a collection of samples like these from around the nation and world, including the Nevada Test Site, Rocky Flats, the Trinity Site, Chernobyl and Palomares, Spain. In total, he estimates having analyzed some 50,000 samples.

The science is arcane, but essentially he’s able to date plutonium contamination based on its ratio of two different isotopes. That is, the plutonium that goes into bomb cores, or “pits,” is mostly weapons-grade plutonium, or plutonium 239, but there is also a small amount of plutonium 240 in the mix. It is this ratio that helps Ketterer distinguish different time periods in the lab’s operating history. The earliest pits — the ones used in the atomic bombs for the Trinity Site and Nagasaki, for instance — had very little plutonium 240 compared to later recipes. 

Ketterer said that the contamination he found in Acid Canyon had even less plutonium 240 than those weapons “making it some of the oldest plutonium ever produced.”