Devil's in the details for drinking water accident scenarios

Residents of Tokyo and other areas around the failed Daiichi power plants have been faced with a whiplash of advisories on the safety of tap water in the face of tests showing the presence of radioactive iodine.

Tokyo officials warned Wednesday that infants should not consume tap water, only to rescind the advisory yesterday when radiation levels tested lower.

It is not clear what the precise route of exposure is through which Japanese water supplies have picked up detectable levels of radioactivity, but the rapid-fire warnings, which have led to bottled water shortages at markets serving Tokyo's 13 million people, raise questions of how U.S. authorities might cope with a similar situation at home.

One place to look? The Quabbin Reservoir in Massachusetts, one of two reservoirs supplying the bulk of demand to the city of Boston.

Located about 30 miles south of the Vermont Yankee Nuclear Power Plant in Vernon, Vt., the open-air reservoir is the largest man-made one in the United States and falls within a 50-mile "ingestion pathway zone" that extends around the nuclear plant on all sides.

Vermont Yankee has been under a cloud recently as Vermont lawmakers have voted to close the plant, citing safety concerns, when it reaches the end of its operating life next year. But the Nuclear Regulatory Commission determined this week that it should be given a 20-year extension on operations.

Vermont Yankee is of the same design as the nuclear reactors now failing in Japan, though the area is not prone to natural disasters like those that hit Fukushima (Greenwire, March 16). Still, officials believe they are prepared for an emergency.

"Quabbin is within the 50-mile extended zone [around Vermont Yankee] which, following an event, water as well as any farms, food production, any food processing would then go into a monitoring phase to see if then there would be any embargoes on such products," said Peter Judge, a public information officer with the Massachusetts Emergency Management Agency.

The main concern, Judge said, is that particulate matter from a release plume could contain radioactive isotopes that, depending on prevailing winds and factors like the type, scale and duration of the release, could fall to the ground within the 50-mile zone and contaminate food and water supplies.

Immediately following an event, Judge said, if conditions warranted, then public health warnings would advise people to avoid potentially contaminated drinking water. "That part of the state is much more rural, much of the water supply is on-site [from] wells, personal wells as well as local wells. So I'm sure the outreach would be to at least immediately, short-term, wait for testing and determination for your water that is not covered," he said.

Beyond that point the emergency measures become more subjective, Judge said, as officials would assess the need to warn Boston residents of a potential hazard or, for example, shift to backup supplies from other area water sources.

Such backups were used for a three-day interruption last year after a water main break, and city residents were warned to boil water as a precautionary measure because the backup supplies were not treated to the same standard as the Quabbin supply, but Judge said the source switch-over and switch-back took place smoothly.

But he conceded that other parts of the state where water supplies could become compromised in a nuclear emergency -- or other parts of the country -- "wouldn't have the luxury of this kind of system" with a robust, well-integrated backup.

And how long a metro area like Boston and its 30 surrounding communities that depend on the Quabbin Reservoir could go without that source is not clear.

Long-term vs. short-term exposures

In Tokyo, the initial warnings that infants under a year of age should not drink tap water was based on a government warning that tests detected 210 becquerels per liter of radioactive iodine-13. The Japanese standard for infants' exposure is not more than 100 becquerels per liter, while the tolerance for adults is 300 becquerels per liter.

An advisory yesterday for American citizens by the U.S. embassy in Tokyo extended slightly more widely, advising that children from newborns to three years, as well as pregnant and nursing women, avoid drinking the water.

"The U.S. [EPA's] published standard for Iodine-131 contamination in drinking water is 3 picocuries per liter, which is equal to about 0.1 becquerels per liter," the embassy said, adding that "the science of radiation protection has advanced considerably since the EPA standard was published in 1974."

"If one uses the latest science and makes the adjustments in the calculations underlying the EPA standard in order to make it applicable to the temporary exposure occurring in Japan, one obtains a figure practically identical to the standard that the Japanese authorities are applying," U.S. officials said.

In an update posted this morning, though, the embassy said that "in accordance with guidelines that apply to water in the United States" and based on analysis of tap water samples from the day before, Tokyo's drinking water was safe for general consumption.

The question of how long water warnings might last in future events depends not just on fickle water sample tests but also on the types of radioactivity involved.

Iodine-131, the isotope that public health officials have said was found in Tokyo's water, has a particularly short half-life of eight days, meaning that half of the radioactivity dissipates in that time. The rule of thumb is that radioactivity becomes negligible after 10 half-lives, when about 1/1,000 of the original amount remains -- in the case of iodine 80 days, or a bit less than three months.

But cesium-137, another isotope that has been tracked in the Japanese disaster, has a half-life of about 30 years, meaning that radioactivity remains a concern for about 300 years after particles enter the atmosphere.

Ed Maher is an environmental consultant with a doctorate in radiological health and protection from the Harvard School of Public Health, who now serves as president of the Health Physics Society, a scientific organization of radiation safety professionals.

Maher downplayed the risks to the Quabbin Reservoir from its proximity to Vermont Yankee, saying the "worst possible contamination in a water supply are 10 to 100 times what you have now" in Japan.

Maher acknowledged that radioactive contamination from isotopes like cesium that have long half-lives could be more damaging long term than even a disastrous release of iodine, because of its relatively quick radioactive decay.

Iodine is particularly likely to be the culprit in long-distance contamination in a release like that seen in Japan, he said, because it is more volatile than many other radioactive materials that could be produced and thus more likely to enter the atmosphere, only to condense on particulate matter in the air and settle back to earth. Think of it as dandelion seeds, spreading on the wind.

Many other potential contaminants are heavier, making them less likely to travel long distances from the plant, he said -- poppy seeds, perhaps, that will fall quickly with gravity.

Maher stressed that doomsday accident scenarios are highly unlikely given the controls on nuclear plants. But should serious contamination from long-lived radioactive material occur, he said, water sources could potentially be treated.

Today, some water sources -- including several in Maine, for example, where radon gas is prevalent in groundwater -- must be treated before meeting EPA's drinking water standards for radioactivity, Maher said. Methods exist to treat a variety of types of radiation, whether by aerating the water to let radon gas bubble out, as is done in affected areas in Maine, or using other techniques to eliminate dissolved or particulate radiation that might be present.

Some particles cannot be removed, Maher said, and it is possible that water could be treated to a large extent, but not sufficiently to meet drinking water standards. But as an extreme example, he said the water that keeps spent fuel rods cool in storage ponds can be treated to a standard that would make it safe to drink. Indeed such water is routinely treated to a high degree to keep it from corroding the fuel rods it protects.

"You could decontaminate a huge body like the Quabbin Reservoir," Maher said, though it would be "a huge undertaking" and "right now there's no way that you could do that." But faced with an unprecedented radiological challenge, the scientific tools exist to tackle the engineering challenge.

Maher said that while to many people looking on the events in Japan appear unprecedented, specialists who mitigate radiation risk all the time do not see it that way. "This is not the first rodeo for a nuclear accident," he said.

Reasonable limits

Janet Johnson is an environmental consultant and is a past president of the Health Physics Society, who now works primarily on radiation related to uranium mining and processing.

Johnson said EPA's drinking water standards are generally reasonable, reflecting a conservative approach appropriate to the lifetime exposure risk of an individual drinking 2 liters of water per day, daily for 70 years.

For the radioactive iodine exposure seen in Japan, she also generally endorsed the Japanese standards. "In terms of overall risk, I think the Japanese standards are reasonable for temporary use of that water," she said, though they would be too high for continuous use for a year.

Rapidly growing children are more sensitive to the effects of radiation, Johnson said, which is why lower tolerances are used for the very young.

Johnson said the Japanese standards do not appear overprotective, but judging them requires balancing relative risks. "It depends on what the alternatives are," she said. "If it comes to a matter of whether you're going to become dehydrated because you're not drinking enough water, that's a more significant risk" than drinking water contaminated even at the earlier, higher test levels reported in Tokyo.

Johnson said adults' "temporary use" of water contaminated at the higher levels seen in Tokyo could be safe during the three-month time period over which radioactivity in iodine decays away.

In general, she said people's fears about radiation -- stemming in part from unfamiliarity and the fact that you cannot see or smell the threat when nearby -- are not fully rational.

Naturally occurring radiation is everywhere -- in drinking water from minerals in the ground and in all indoor environments from the radioactive decay of radon gas, for example.

"The fact is that we do live in a radioactive environment," Johnson said. "That's the way the Earth is constructed, and radiation is not some strange, alien force -- it's part of our environment and always has been."