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Wednesday, Nov. 9, 2011

News photo
Unwanted earth: A heap of waste and soil collected during a decontamination program is piled up in the garden of a house in the Onami district in the city of Fukushima on Oct. 18, the day the city kicked off a cleanup drive that will last two years. KAZUAKI NAGATA

Q&A

Scrub homes, denude trees to wash cesium fears away


Staff writer

Worried about radioactive fallout from the Fukushima No. 1 nuclear plant? Don't wait for the government to help.

News photo

Experts advise people who live in and near Fukushima Prefecture where they face cumulative annual radiation exposure exceeding 1 millisievert — the legal limit for the general public — to quickly take the initiative in removing irradiated soil and other material where fallout might accumulate in their vicinity, instead of waiting for the government to carry out decontamination work.

Annual radiation exposure of 1 millisievert translates into 0.23 microsievert per hour, according to the government. Such readings have been observed in areas in the Kanto region, including Nasu in northern Tochigi Prefecture and Kashiwa in northern Chiba Prefecture. In Tokyo, only the Okutama forest area has had similar fallout.

In many cases, significant decontamination can be achieved by a few simple procedures. Following are tips for do-it-yourself home decontamination:

What's the first basic step?

The Japanese Society of Radiation Safety Management's decontamination manual advises people to clean off surface areas where radioactive cesium may have landed.

Large amounts of the isotope attach to soil, roofs, walls, leaves and surfaces of other foliage.

If people have a general awareness of where cesium is likely to accumulate and take proper safety measures, they can reduce the radiation levels where they live, experts say.

Should protective clothing be worn for decontamination work?

Fukushima Prefecture's guidelines recommend wearing a hat, face mask, gloves, waterproof boots, long-sleeved shirt and long pants to lessen external and internal exposure, and experts add that the garb should be disposable.

When decontamination efforts involve use of water, the guideline advises rain gear and eye protection, plus a helmet and safety line when cleaning roofs.

Where should one start the decontamination?

The first step is to measure radiation levels on the roof, downspouts and lawns to detect mini hot spots and other places that are highly irradiated and need thorough decontamination.

An accurate reading, however, may only be provided by a sophisticated, and thus expensive, dosimeter.

Shogo Higaki, a research associate in chemistry at the University of Tokyo's Radioisotope Center, said many cheap dosimeters that can be purchased online are unreliable.

"If you don't have an accurate dosimeter, then focus on cleaning likely hot spots, such as the end of downspouts," where rainwater from the roof accumulates, Higaki said.

Some local governments lend out dosimeters. But in many cases the demand is so great that there's a monthlong waiting period.

For example, the city of Nikko, Tochigi Prefecture, began lending out 23 dosimeters to its residents on Oct. 11, and the applicants exceeded 300 just in three days, a local official said.

What's the next step?

Remove all garbage and fallen leaves before spraying water on soil and grass to prevent contaminated dust from being stirred up.

Then start washing from higher places down. For roofs and walls, some experts advise high-pressure sprayers — which can be purchased at home centers — or use a scrub brush to scrape off radioactive cesium from surfaces.

Other experts advise, however, that unless tainted water from a pressure wash can be captured, it will only work its way into the sewer system or other drains, some ultimately flowing to the sea.

Radioactive isotopes can be removed more easily if the cleaning water contains sodium bicarbonate or two- or three-parts vinegar, JRSM advises.

As for rusted downspouts or other surfaces that are highly likely to be tainted, use abrasive powder to remove cesium.

Because cesium adheres strongly to a roof, it's important to carefully spray every nook and cranny, Higaki of the University of Tokyo said. It's also important to remove fallen leaves, dirt and in some cases moss from downspouts and gutters.

In the case of soil, most of the cesium is on the surface to a depth of 5 cm, and thus removing this much can ease the problem, Higaki said.

Cesium-134 and -137 emitted from Fukushima No. 1 "is trapped within 5 or 6 cm deep in soil . . . (but) from a density point of view, topsoil has the highest amount and it gets lower the deeper it gets," said Higaki, who has conducted decontamination experiments at homes in the Fukushima city of Koriyama.

Bushes, plants, grass, weeds, cobblestones and other surfaces covering the ground may have to be removed before surface soil is scraped away, experts said. When removing weeds, make sure to pull them out from the roots, the city of Fukushima's decontamination manual advises. As for trees, it's best to remove all their leaves because of the likelihood they contain large amounts of cesium, Higaki said.

Where are likely hot spots to crop up other than at the bottom of a downspout?

Places where water, dirt or leaves accumulate are the usual suspects. Zinc-roofed structures also easily trap radioactive particles, according to the science ministry's guideline on radiation measurements. On the other hand, smooth surfaces, including plastic and painted areas, are unlikely to catch cesium, experts say.

What should you do with the soil and leaves?

Put all the waste into plastic bags and bury them on your property, covering the hole with 20 cm to 30 cm of soil and plastic tarps, until they can be removed to longer-term, but still temporary, municipal storage sites.

Leaves and weeds can be disposed of as burnable garbage, a Fukushima official said.

What should be done after completing the work?

Gargle, shower or bathe to rinse off all dirt, the prefectural guideline recommends.

Disposable garments should be placed in garbage bags and clothing not to be discarded should be washed like usual laundry, it says.

Where will tainted water used in decontamination work eventually end up?

Much of it will probably be routed through sewage treatment plants, and some will flow to the ocean, Higaki said.

Cesium in the tainted water may accumulate as highly polluted sludge, as is often found at sewage plants. Many plants are temporarily storing such sludge because they have yet to find a safe place for final disposal.

Thus some experts urge people not to use pressure washes.

Kunihiro Yamada, a professor of environmental design at Kyoto Seika University who has been conducting decontamination in Fukushima, suggests in his decontamination manual to use PVA liquid glue — often sold as laundry starch — to remove cesium from roofs and other surfaces.

By following all the recommended steps, will radiation levels decline to the pre-March 11 state?

No. Experts note just cleaning up one's own property will only achieve limited results.

Higaki said when residents of Koriyama decontaminated their homes, radiation levels declined by about 60 percent, from 3 microsieverts per hour to 0.5 microsievert per hour. To lower the level further, decontamination of surrounding areas is needed.

"Gamma rays from cesium have a reach of about 80 meters. So to ensure a greater decontamination, cleanup efforts must extend to wider areas," Higaki of the University of Tokyo said.

So if a house is next to a park or forest, it will be extremely hard to lower the area radiation level, Higaki added.

Given that about 70 percent of Fukushima is forested, removing the radioactive fallout will be an extremely tall order.

Do Tokyoites also need to decontaminate their property?

This has so far not been advised, as atmospheric radiation levels in most of the metropolis are now at normal levels, Higaki said.

Having said that, he advised the removal of surface soil and moss, dirt and leaves if a small hot spot is found, such as the case at an elementary school in Adachi Ward where the radiation reading near the end of a gymnasium downspout hit 3.99 microsieverts per hour in October.

Radioactive fallout from the Fukushima plant tends to accumulate at the same locations even after decontamination work. So Higaki advises that potential hot spots be monitored once every few months. If the radiation rises again, decontaminate again. Such ad hoc steps can help reduce the radiation in areas of low contamination, he said.


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