Strange story of the spilt radioactive pellets

Press, 18 May 1984, Page 14

Strange story of the spilt radioactive pellets

Five months ago, a Mexican electrician forced open an unmarked capsule filled with 6010 tiny, silvery pellets that looked like cake decorations. He paid little attention as they spilled into the tray of his pickup truck and on to the road, and later throughout a junkyard in his hometown of Juarez, just across the Rio Grande from El Paso, Texas. At that moment the electrician unwittingly caused what is now being recognised as potentially the worst spill of radioactive material in North American history. Since then, more than 200 people have been exposed to radiation from the tiny pellets of cobalt 60 that had once been the core of a cancertreatment device.

The full dimensions of the spill, which the officials said has released radiation 100 times more intense than the nuclear accident at Three Mile Island in Pennsylvania, are still unknown because the incident was so unusual. Unlike most nuclear accidents, in which one or two people are exposed to a brief burst of high radiation, this one involved scores of people exposed to low but significant levels of radiation intermittently over a long period of time.

Mexican officials say it is too soon to know if the people exposed to the radiation suffered any longterm health effects. Even so, 10 people exposed in Juarez have undergone chromosome tests, and all showed damage, the authorities said. f h “Ih’ terms of how many jieOple

were potentially exposed and the duration of their exposure, it could be the most serious radiation accident in North America,” says Karl Hubner, a leading radiation accident expert at the Oak Ridge Associated Universities in Tennessee.

Most of the cobalt 60 pellets were scooped up by a giant junkyard magnet, mixed in with other scrap metal, and taken to two Mexican foundries, where they were melted into steel reinforcement rods and restaurant table legs. Thousands of tonnes of this “hot” metal were then shipped throughout Mexico and the United States.

Meanwhile, hundreds of the pellets remained in the back of the electrician’s pickup truck, which sat parked for eight weeks in a busy neighbourhood of Juarez. People walked by the truck every day, and neighbourhood children played on it. Mexican public health officials said that about 200 people were exposed, but that most are believed to have absorbed relatively low levels of radiation. The device involved in the Juarez accident was a Picker 3000 cancer therapy unit. Manufactured about 20 years ago, it contained small pellets of metallic cobalt, made radioactive in a nuclear reactor, that were placed in a stainless steel container. This capsule was sealed in a tungsten wheel the size of a tricycle tyre, which was then placed behind thick lead shielding. j Radiation emitted through'' a

pinhole in the lead was used to treat patients with localised cancers. About 1000 newer cancertreatment machines using the same principle are in use today throughout the United States.

In 1977, a Lubbock, Texas, hospital sold the unit to an X-ray equipment company in Fort Worth, which in turn sold it to a medical clinic, Centro Medico, in Juarez. According to the United States Nuclear Regulatory Commission, the sale was legal even though the clinic in Mexico had no licence to receive radioactive materials. Once in Juarez, however, the machine sat in a warehouse. Doctors at the clinic said they were never able to hire the specialist required to operate the device. Then, late last November, an electrician, Vicente Sotelo, said he was told to go to the warehouse to pick up some material and to take it to the Jonke Fenix junkyard in Juarez. He and a co-worker heaved the radioactive tungsten wheel, which had been removed from its enormous lead casing, into the back of a pickup truck. Sotelo later told the authorities he forced the unmarked capsule open on the back of his truck.

Doctors at the clinic say Sotelo was not authorised to take the wheel containing the capsule, which he sold to the junkyard for $9. No charges have been filed, and Mexican authorities say they are still investigating the incident. When the capsule was breached it held about 400 curies of radioactive cobalt in the 6010 pellets. Each pellet, according to Joel

By

SANDRA BLAKESLEE,

“New York Times”

Lubenau, a health physicist at the Nuclear Regulatory Agency, produced a radiation dose of 25 rads per hour five centimetres from the pellet. One to 50 rads per hour is considered a significant radiation dose. In comparison, the highest exposure a bystander could have received from the nuclear accident at Three Mile Island in Pennsylvania was 100 millirads, or about one-tenth of a rad. A rad is a unit of absorbed radiation. An average chest X-ray produces 20 to 30 millirads instantaneously. A lethal dose for half the population is 450 rads received instantaneously over the whole body. “If you sat next to a pellet over many hours, you might several days later develop a reddening of the skin,” Dr Lubenau says. “If a pellet became embedded in your shoe you could get localised high exposure to the body.” By December 6, Sotelo had thrown the capsule off his truck into the salvage yard. The date is known because all paperwork from the junkyard dated December 6 or later is radioactive. About 60 curies of cobalt remained on the truck, which Sotelo drove home to his neighbourhood in another part of the city. It stood parked for eight weeks, most of the time with a flat tyre, near a row of jback-street houses. Children played Am and near the truck. People

passed it every day, including Sotelo’s own family. The truck was dangerously “hot.” From one metre away, it emitted 50 rads an hour of radioactivity. “It was a large source that can give whole body exposure,” Dr Lubenau says. “Most people at 100 rads or so will start demonstrating physical signs of radiation injury.”

These include a decrease in white blood cells, which protect the body from infection, and blood platelets, as well as temporary damage to the body’s chromosomes.

Meanwhile, the capsule containing the remaining cobalt pellets — 340 curies worth — was contaminating the junkyard. It was dumped near an enormous magnet used to pick up and load scrap metal on to trucks, the metal to be recycled at Mexican foundries. The capsule was made of nonferrous metal. Every time it was scooped up by the magnet, it eventually fell to the ground, spilling out cobalt pellets like salt from a shaker. The pellets were ferrous. The magnet picked them up and mixed them into the scrap leaving the junkyard. Some pellets were pulverised and thoroughly spread across the huge junkyard, and others are believed to have become embedded in truck tyres and spread along highways. In Ulis manner, 300 curies of radioactive cobalt made its way to

two foundries. One in Juarez manufactured metal table legs and sent them to the largest distributor of restaurant tables in the United States. Another in Chihuahua produced about 5000 tonnes of rebar, or steel rods used to reinforce concrete in building projects. About 600 tonnes of the contaminated steel was shipped to the United States in December and January. When a delivery truck took a wrong turn near the Los Alamos National Laboratory in New Mexico on January 17, a radiation alarm was tripped. Thus, by accident, did the American and Mexican authorities learn of the contamination. It was quickly traced to the junkyard, which was closed on January 20. Sotelo’s truck was impounded on January 26. American officials say they tracked down all the table legs and rebar in February and March, and have returned the material to Mexico. While there were a few “hot spots” of up to 600 millirads per hour, most of the metal produced very low levels of radiation and never posed a serious health threat to Americans who came in contact with the metal, they add.

But Mexican officials have had a much tougher job. About 40 curies of the cobalt pellets remained spread around the junkyard. It took two months to mop up there. Pellets could have been dropped anywhere on the roads between Juarez and Chihuahua. Last month, a special reconnaisance helicopter provided by the United States Department oPEnergy flew over

the area and found 22 radioactive sites. Eight pellets were dug out of highway pavement. Such material, along with the radioactive truck, is now in a special holding area near Juarez, waiting to be buried at a safe disposal site, says Roberto Trevino of Mexico’s National Commission for Nuclear Safety and Safeguards.

Thousands of tons of contaminated rebar, however, have spread into four or five Mexican states. Hundreds of new homes built with the rods may have to be torn down. The accident has been costly to Mexico, but the greatest toll may be levied on the people who were most exposed to the radioactive cobalt. The problem, Mr Hubner says, is to figure how to identify the people who were exposed and what doses of radioactivity they encountered. One standard method of assessing radiation exposure, which costs about ?1000 per person to conduct, involves looking for chromosome damage. It is controversial because it cannot predict long-term health consequences of radiation exposure.

White blood cells of 10 Juarez residents, four people from the neighbourhood and six junkyard workers, were cultured in Hubner’s laboratory. As the cells were allowed to divide 500 times, the number of broken or aberrant chromosomes were counted. This number was then used to estimate the dose of radiation received.

It appears that several people were exposed to l§o or 200 rads, Professor Hubner -'says, which is

higher than the doses received by Marshall Islanders who encountered radioactive fallout from United States nuclear tests. Those with the highest exposures included two junkyard workers, one of Sotelo’s neighbours, and the man who helped Sotelo load the cancer device off the truck. Sotelo apparently escaped serious contamination.

However, “broken chromosomes only tell us there was damage and nothing about its biological consequences, ■’ Professor Hubner adds. “It is not predictive in terms of genetic effects or future cancers.” Meanwhile, the junkyard workers and families are being monitored by Mexican health officials. One man received a radiation burn on his hand, Mr Trevino says, and others experienced blackened fingernails and reduced sperm counts. But blood counts appear to have returned to normal, he adds, and no one seems to have suffered serious health complications. Concern over the implications of the incident continues. American officials, worried that more contaminated rebar might make its way into the United States, have asked the Nuclear Regulatory Commission to place scores of radiation detectors at all major border crossings.

Mexican and United States officials have discussed ways to help one another finish cleaning up the Juarez accident, to monitor the health of people exposed to radiation, and how to prevent future accidents. L