One of the few patches of earth that Chernobyl radiation made entirely uninhabitable was, ironically, one of the first parts of Europe to be inhabited by modern humans. When continental ice sheets blanketed much of Belarus during the last Ice Age, the zone was part of a periglacial steppe. It was a forbidding, arid tundra periodically plagued by blinding dust storms of silt called loess that blew in from the glaciers. But about 25,000 to 30,000 years ago, small bands of hunter-gatherers made their way north from Africa. Equipped with fire, warm clothes, and sturdy mammoth-bone dwellings, they

were able to brave the daunting conditions for the superb hunting opportunities offered by large grazing herds of mammoth, bison, and ancient horses.

People stayed on after the glaciers retreated 12,000 years ago and tundra steppes gave way to forests and swamps. As human populations grew and Ice Age game such as mammoth disappeared, new generations of hunter-gatherers aimed for nimbler quarry like deer but turned more and more to fishing and gathering the fruits of the forest for much of their food. When the Neolithic revolution brought pottery from the Near East to north of the Black Sea around 5500 B.C.E., the denizens of what is now Polissia impressed their pots with comb and pit symbols that made them part of a larger archaeological identity known as the “Comb-and-Pit” culture.

There is little evidence that the forest dwellers moved very much over the mute millennia that followed, although combs and pits were followed by a succession of different pottery, tools, and weapons that hint at the cultural morphing and tribal mixing that culminated in the first written reference to the Comb-and-Pit folks’ descendants. In the fifth century B.C.E., the Greek “father of history” Herodotus wrote of a people he called the Neuri, who lived in the region before being forced to abandon it by an invasion of snakes.

The Neuri were most likely Iron Age Balts, and the snakes that chased them out may have symbolized Slavs. In any case, the next written mention of the forest denizens identified them as a Slavic tribe called Drevlyany, or Derevlians. With a name derived from derevo (or drevo in the ancient form), which means “tree,” the woodland Slavs were one of the founding tribes of Kievan Rus’—the medieval state to which Belarusians, Russians, and Ukrainians trace their roots. Indeed, the place name “Chornobyl” first appeared in an 1193 charter that described a Kievan Rus’ prince’s hunting lodge.

In the centuries after Kievan Rus’ declined, the Drevlyany lands passed politically from the Grand Duchy of Lithuania to Poland, from Poland to Russia, and from Russia to the Union of Soviet Socialist Republics (with a brief interregnum in the short-lived independent Ukrainian republic); then, after the USSR’s collapse in 1991, they were split between independent Belarus and Ukraine. But the people who lived there—like more than half of Ukraine’s population—remained largely of the same genetic stock as the original Ice Age mammoth hunters. Their evacuation in Chernobyl’s wake brought an abrupt end

to some 25,000 years of continuous—if not uninterrupted—settlement in one of humanity’s most ancient European homelands. Yet the sad cultural absence of people has allowed nature to resume its primordial patterns and cycles. Only now, radiation has become their integral part.

If all you have is a cheap handheld dosimeter, you may as well keep it in your pocket when strolling in the Red Forest. I learned this rather quickly when mine simply shut down from the overload of being in multiple milli-land.

Rimma Kyselytsia, the Chernobylinterinform guide, and Svitlana Bidna, the botanist, meandered with me on a freezing, gloomy day in a forest of pygmy pines, twisted and bushy like the trees that grow on leaky nuclear waste dumps and then some. In fact, some plants resembled neither bush nor tree.

Svitlana stopped by one pine that had started out normally, with more or less perpendicular branches, but then sprouted what resembled a large upright broom from the top. Another pine was twisted into filigree (Plate 3).

I wished that we had a more powerful dosimeter to let us know what the exact levels were. But there were few places in the Red Forest with levels lower than five milliroentgens an hour. This meant that if we stood in such places for six hours, we would be exposed to the equivalent of a chest X ray (30 milliroentgens).

Looked at another way, the maximum dose considered safe for people who work in the nuclear industry is 5,000 millirem—which is the same as five rem—a year. For civilians, the limit was a tenth of a rem a year. We’ll define “rem,” “roentgen,” and other radiation units later, but for now we can consider rem roughly equivalent to roentgens. Although I wasn’t sure if I had entered the category of quasi-nuclear worker by writing a book about Chernobyl, I knew that the Red Forest was not a place in which I wanted to spend too much time.

Actually, the name “Red Forest” is a misnomer because it isn’t red and, with its short and stunted pines, it isn’t much of a forest either. But in 1986 the four and a half square miles of evergreen woodlands stood directly in the path of the deadliest debris from the explosion and then turned red before they died.

Those trees and about 1 million square meters of topsoil were bur-

ied on the spot in a “point for the temporary storage of radioactive waste” and covered with four feet of sand. The sand was sprayed with a liquid polymer that hardened to keep it from blowing away. After 15 years, there were still patches of polymer here and there, like flat sandstone pancakes that are easy to spot because nothing grows on them. Indeed, had the polymers not cracked and disintegrated, parts of the zone would resemble a barren moonscape to this day. But the sand was eventually planted with the young pines that surrounded us. Although the pines—regardless of their strange shapes—are green, the nickname Red Forest stuck and it now refers to one of the most radioactive outdoor environments on the planet.

The trees themselves are very radioactive, too, containing up to 500,000 becquerels of cesium and 7 million becquerels of strontium in a kilogram of wood!

Rimma flicked her chin at the surrounding expanse of stunted trees. “There are places in the Red Forest where background is one roentgen an hour.”

The last sentence was much easier to write than to experience. It is one thing to sit in a safe office and write about what radionuclides do in the wild. It is quite another thing to stand in their midst while guides toss around alarming figures. One roentgen was a lot. Though I try to affect nonchalance when the gauges start inching into the milli-range, and usually succeed well enough to avoid the patronizing smiles that excessive radiation fears can prompt in zone professionals, my concern was obvious.

Rimma smiled, but without patronizing me. “Don’t worry,” she started to say before I interrupted: “You always say that.”

“I say it when it’s true. Those high levels are at isolated points, hot spots,” she explained. “We know where they are and we’re not taking you there. Besides, one roentgen measures the radiation you’ll be exposed to in an hour. It doesn’t mean that you’ll get a dose of one rem.”

“I knew that,” I responded, just a split second too quickly.

Radiation exposure, measured in roentgens per hour, can be likened to a battlefield where the air is streaking silently with invisible particles and rays. The fiercer the exchange of artillery, the higher the exposure will be. Even if you were to stand in the midst of battle, though, not every rocket or bullet would hit you. Those that do make up your absorbed dose are measured in units called “rads.” But in the same way that being nicked on your arm by a bullet differs from being

shot in a vital organ, radiation has different biological effects—even for the same amount of absorbed dose—depending on the type of tissue it hits and whether the radiation is alpha, beta, or gamma. Biological impact is measured in rem units. For gamma rays and X rays, the rem dose is the same as the roentgen exposure. Dose is the same as exposure for beta particles as well. But for heavy and energetic alpha particles, the rem dose is 20 times the exposure level.

Based on morbidity and mortality rates after the atomic bombs were dropped on Hiroshima and Nagasaki, an acute dose of 100 rem is the minimum needed to trigger acute radiation illness. Acute doses of 300 to 500 rem will kill most people, although new treatments have increased survival rates. Acute doses of more than 1,500 rem will kill anyone.

From this perspective, one roentgen didn’t seem so bad—especially since nearly all of the radiation exposure you get in Chernobyl these days is chronic, not acute. Besides, it was far away. Like staying off the battlefield, the greater your distance from a radiation source, the less likely it is to lob you with its atomic artillery.

There, however, the battlefield analogy breaks down. If the atomic world behaved anything like the classical physical world in which we live and where real battles take place, radiation would be impossible. In the classical world we experience with our senses, a bullet can put a hole in a wall and emerge from the other side. No matter how many times that bullet is shot, however, it will never pop through the wall without leaving a trace and suddenly appear outside it.

But that is exactly how an atomic nucleus emits radiation. In fact, it only appears to be “emitting” to us, as we imagine, say, an alpha particle shooting through the nuclear boundary like a bullet. But this is impossible. No alpha particle is energetic enough to escape the strong force. What it can do, however, is some quantum magic because it has a dual personality as a wave. It isn’t a physical wave like a gamma ray. It has no energy and can’t be detected because if it is detected, it immediately stops being a wave and becomes a particle.

The quantum wave reflects the weird subatomic reality that a particle such as an alpha becomes an alpha—that is, an identifiable thing with dynamic attributes like speed and position—only when it is measured. Now, measuring a quantum particle is in and of itself a paradoxical, controversial, and poorly understood process at the interface of mind and matter, which seems to require both consciousness and

ignorance. But before that act of measurement takes place, the alpha exists in the abstract form of a mathematical formula known as a wave function. Symbolized by the Greek letter ψ, or psi, the wave function represents the statistical probability of finding that alpha in a particular place at a particular time. Before they are measured, the probabilities are smeared all over the place. Measuring psi focuses those fuzzy probabilities into a specific place and time.

Because of the fundamental quantum uncertainty about where—and whether—anything really “is,” the subatomic occupants of a nucleus are less like bullets in a gun and more like the water in a washing machine. The particles’ probabilities spin and cascade around inside, sloshing and splashing against the energy barriers imposed by the strong force. If the nucleus is filled normally, as in a stable isotope, the probabilities will always splash back inside. Although the universe is mind-bogglingly large and full of wonders for which our imaginations are inadequate, a stable atomic nucleus has never been known to decay.

However, if it is overfilled, like a radioactive nucleus, some of the probability eventually leaks outside the energy barrier. If the barrier is small and the leaking ψ is large enough to penetrate it, the probability of finding the particle outside the nucleus becomes not zero and, therefore, not impossible. In the quantum world, anything that is not impossible sometimes happens. So, if a droplet of psi leaks out of the barrier, it can pull the rest of the probability wave with it, making it appear that a particle has “tunneled” out of a nucleus without leaving any physical trace that it had passed through.

The same principle fuels fission, except in the reverse, when a neutron tunnels into a nucleus. That’s why slow neutrons are better at fission than fast ones: neutrons that move slowly are in the vicinity of a nucleus longer, giving their probability wave more time to leak inside.

In quantum terms, the Red Forest was leaking a lot of probabilities. As we trudged through the packed sand among the twisted pines, I wondered if there was any deeper significance to the fact that ψ looks much like a stylized trident, the symbol of the Kievan Rus’ princes that the first independent Ukraine adopted as its state seal in 1918, followed by the second independent Ukraine in 1991 (Figure 2). In fact, the classic trefoil symbol of radiation was also a tri-sign.

Svitlana motioned for us to gather around a straggly pine. With a

FIGURE 2 Tridents over the ages.

gloved hand, she fingered a branch that was bare but for a few clumps of stunted, tightly bunched needles that resembled thistles.

“Normal pine needles are supposed to be about an inch long and grow in pairs on either side of the branch. Radiation damages their spatial orientation so the shoots grow in the wrong direction and in the wrong places,” she explained, pointing out another branch that had sprouted curly minibrooms. “In the early days, there was a lot of radiomorphism. Now you just see it in places like the waste dumps and here in the Red Forest.”

Since the dawning of the nuclear age—especially in the late 1950s and 1960s when there was growing concern about the effects of fallout from atmospheric nuclear testing—much has been learned about what acute external radiation does to plants at places such as the Savannah River site in the U.S. Department of Energy’s nuclear weapons complex. But nothing in the outdoors of any DOE facility compares to the levels and extent of radiation in the Exclusion Zone, where scientists (including scientists from Savannah River) can comprehensively study the effects of chronic and constant radiation exposure on vegetation in the wild, with many surprising conclusions.

As we shall see, Chernobyl’s radionuclides behaved very differently in the wild than anyone expected. But initially, they did what any kind of fallout will do: they stuck to things (Plate 4). The end of April is early in the growing season for Polissia. In 1986 the collective farms’ fields had already been sown and leafy trees were just beginning to bud, so it fell to the conifers to intercept as much as 80 percent of the radioactive cesium that coated the 30-kilometer zone. Fallout stuck especially strongly to wrinkled leaves, where hot particles could embed

in the creases, and also on sticky surfaces like those on buds, leaves, needles, and certain flowers. Given their sticky resin and gnarly bark, pines were particularly magnetic.

With fallout on just about everything in the surrounding environment, the plants’ radiation doses were partly external, primarily from gamma rays. But their greatest doses came from the radionuclides stuck to their own surfaces and bombarding them not only with gamma rays but also with alpha and beta particles, whose biological damage capability increases at tiny distances.

Because radiation does the most damage to cells that are actively dividing, growing organisms are most vulnerable to its impact. In mammals, active cell division and growth slow significantly in adults except for cells in the hair, skin, bone marrow, and gastrointestinal tract, which is why high radiation doses cause, among other symptoms, hair loss and vomiting. But a plant continues growing throughout its lifetime, and its most active cells are in the perpetually young tissues called meristems. Located in buds, root tips, and the cambium in the outer layers of stems, branches, and trunks, meristems are like botanical stem cells. With the exception of roots, which were hidden in the ground, these were precisely the plant parts to which radiation adhered, so what did grow in 1986 grew more slowly and much more strangely than usual.

The specific effects depended on the plant species. Radiation resistance among trees, for example, varies widely. Evergreens die at lower doses than leafy trees and young trees are more vulnerable than older ones. The growth of spruce and pine, the most sensitive species, gets stunted at absorbed doses of 150 to 250 rads. But it takes 1,000 to 1,500 rads—fatal for most other trees—to slow down an aspen. Birch and alder are somewhere in the middle.

Inside the 10-kilometer zone, where radiation levels were highest and the doses were close to lethal, plants’ organs changed their shape or size. Leaves and flowers were wrinkled or twisted, or they grew asymmetrically. Irradiation of buds caused smaller, bushier, and more asymmetrical shoots. Norway spruces, oaks, lindens, and horse chestnuts displayed gigantism, sprouting leaves and needles that were much larger than average though their shape was perfectly normal.

In places where gamma radiation was about 30 milliroentgens an hour, field sagewort buds sprouted short shoots, thickly covered with clusters of deformed leaves, while purple loosestrife grew normally at

first, but the tips were thickly covered with narrow leaves instead of flowers.

Although a 30-milliroentgens hourly exposure is far from fatal, a pine needle growing under such a background level can absorb a total dose as high as 500 rads over its two-year lifetime.

Such a prolonged dose doesn’t kill the plant, but does make it malnourished because radiation damages chloroplasts, the photosynthetic cells in leaves that transmute sunshine into sugar, leading to less intense photosynthesis.

Very high radiation doses kill chloroplasts altogether, which is what happened to the Red Forest.

“The trees that stood closest to the reactor died first. In the first days, their exposures were as high as 8,000 roentgens an hour,” said Svitlana as we strolled amid the stunted pines, passing a tall and skinny sapling that was utterly bare of branches but for the top, where three shoots had sprouted.

“The exposure decreased after the short-lived radionuclides decayed and those that remained washed off,” Svitlana continued. “But a pine dies at an absorbed dose of 7 to 11 grays and the dose they accumulated over time was that high in places, so the Red Forest gradually expanded.”

Radiation terminology is complicated enough for the layperson without having to contend with two different systems. Grays are metric units. Although metric units are not in much favor in the United States, except among scientists, they are the only units used in Chernobyl research.

The sievert—named in honor of Rolf Sievert, the Swedish scientist who did much to standardize radiation doses—is the metric equivalent of the rem. One sievert equals 100 rem. The “gray” is the metric unit for measuring absorbed dose. One gray is the same as 100 rads. So, if the Red Forest absorbed 7 to 11 grays, that was equal to 700 to 1,100 rads, a fatal dose. But the dose may not have come just from the radioactive debris and dust. It is possible that the steam that caused the explosion condensed in the cooler air, drizzling radionuclides onto the trees.

The trees’ buds died first, followed by the cambium and needles. The chlorophyll and its green color were also destroyed, giving the forest its color—and its name. After the Red Forest was buried in the summer of 1987, some plants such as bison grass—an herb used to

flavor zubrovka, or “bison vodka”—survived the interment and grew back the following spring, but their seeds were sterile.

Pine trees continued to die over the next several years as trees farther away from the reactor gradually accumulated lethal doses.

Even before the Red Forest’s burial, surface radiation levels in the 10-kilometer zone fell dramatically by the autumn of 1986. Completion of the Sarcophagus put a cap on the lethally radioactive core. Short-lived radionuclides had decayed, bringing hourly exposure levels down to single-digit milliroentgens in most places outside the nuclear station. Though wind and rain are not very good at cleansing plants of hot particles and other fallout, the autumn leaves fell to the ground as the growing season came to an end. Except for evergreens and the trunks and branches of trees and shrubs, much of the Chernobyl fallout wintered on the ground.

The most direct route from Kiev to Chernobyl is a one-lane road that runs alongside the artificial reservoir known as the Kiev Sea and passes though village after village of small houses, hidden behind tall barriers and surrounded by fruit trees whose pastel blooms clothed the spring landscape in delicate hues of pink, ivory, and lavender. On each village’s outskirts, the giant fields of industrialized agriculture were bordered by small rectangular plots, one right next to the other, where the farm workers kept their private gardens. The variegated patterns of each individual vegetable patch blanketed the land like a textured quilt.

Recently returned from their wintering grounds in Africa, white storks glided over the fields, their long red legs trailing like ribbons. Just a few miles outside the zone’s southern checkpoint in the village of Dytiatky, I spotted a colony of 20 storks—the most I had ever seen in a single place—dining in a plowed field. Storks are practically sacred in Ukraine, and their large stick nests bestow favor, fortune, and fertility on any household lucky enough to have one perched on its roof, telephone pole, or chimney. But woe awaits the family whose storks abandon it.

Perhaps that is why white storks have become a symbol for Chernobyl, used to decorate posters and pamphlets about the disaster. In contrast to their shy and rare black stork cousins, white storks like living amid people, in open farmlands near swampy riversides,

marshes, and floodplains stocked with stork snacks such as frogs and snakes—and just like the lands around Chernobyl on the eve of the disaster. But these are now no-man’s-lands.

I thought about storks in the abandoned village of Leliv, which overlooks the Chernobyl station’s cooling pond just inside the 10-kilometer zone. It wasn’t an easy place to reach. Though I was able to drive part of the way on crumbled asphalt through a dense thicket of branches that slapped against the car windows, my companions and I had to get out and walk when we came upon a young aspen that had sprouted in the middle of the road.

Leliv is a moderately contaminated pink patch on the radiation maps and my dosimeter displayed numbers well below its two-milliroentgens limit: 45, 67, and 23 microroentgens an hour. But I couldn’t keep my eyes on it for long because I had to watch my feet. A thick carpet of grasses sprouting with jolly dandelions and plowed into uneven clumps by boars made the going difficult. We couldn’t stop because as soon as we did, swarms of nasty gnat-like bugs enveloped our faces. They didn’t bite, but they were annoying as hell.

After about 10 minutes, we came upon the rotting remains of log cabins. Some of the roofs were of corrugated metal. Others had been thatch, but all that was left were some wisps of dried grass stuck to exposed beams. Part of a stork’s nest rested on a cottage gable, though a large chunk had fallen off onto a jumble of rusted machinery, overturned carts, and other detritus left behind in the evacuation. When the people left and friendly farmlands steadily gave way to feral fields and wormwood forests, the storks eventually left, too, and their nests largely rotted, the debris blown away by wind.

Storks can occasionally be seen in the villages where people still live, though not many, and there are none at all in completely abandoned villages like Leliv. After more than a dozen trips to Chernobyl, totaling about a month’s time altogether, the only stork I ever saw in the zone was painted on a sign that the Chernobyl forestry service planted on a roadside.

A small, dark gray bird with a rust-colored tail and a white wing patch was perched on the cabin’s window frame. It was a black redstart. The birds colonized the abandoned houses after the evacuation.

“This all used to be cultivated,” said Svitlana, waving her arm at the wild fields, thick with bushes, shrubs, and small trees that were consuming the village. “But nature started taking over as soon as people

left. The environment is returning to the way it was in the sixteenth century.”

The forests that covered 80 percent of Polissia in the twelfth century and gave the drevlyanny their livelihood and name were gradually logged over the centuries. By the sixteenth century, only half of Polissia was woodlands. In the nineteenth century, swaths of the region were denuded for lumber and some swamps were drained. The Soviets drained even more swamps and planted trees on about a third of the land after World War II, but they were pine plantations, devoid of diversity. Most of the remaining land was cultivated, although it was hard to believe that the blooming springtime wilderness surrounding us had ever been under the plow. The 1986 fields, sown just before the evacuation, grew without anyone to tend or harvest them, but there wasn’t a trace of cultivated crops that I could see in Leliv.

When we made our way through a stand of young silver birches, their yellowish catkins just beginning to open, I heard what sounded like a kitten quietly meowing. It was a jay, singing on a birch. A big tawny bird with a wing patch of iridescent blue, the European jay’s call is crow-like squawk, though its song is an unmelodic and odd mixture of clucks and meows. It was the first time I had heard it, but when I focused my binoculars on its source, the bird had already flown away.

“Once cultivation stopped in the 30-kilometer zone, succession started almost immediately with wild grasses, herbaceous plants, and shrubs. After 15 years, the meadow stage is completing and tree seedlings are becoming more frequent,” Svitlana continued.

Succession refers to the changes in a plant community that occur over time, creating and filling gaps created by natural (floods, windstorms, volcanic eruptions) and unnatural (cultivation, urban development, swamp drainage) disturbances. A cleared woodlot is quickly colonized by the trees that remain in the vicinity. A pasture can eventually give way to a forest. Wetlands are re-created when neglected drainage ditches get clogged with silt. Given that the 30-kilometer zone may be uninhabited for about 300 years—the 10 half-lives that it will take for cesium and strontium to decay to relatively safe levels—it will have plenty of time to revert to its swampy woodland origins.

Actually, Chernobyl released several cesium and strontium isotopes with different rates of decay. Cesium-134 has a half-life of about 2 years, while that of cesium-137 is 30 years. Strontium-89’s half-life of 50 days is much, much shorter than strontium-90’s 29 years. At the

turn of the millennium, only cesium-137 and strontium-90—abbreviated as Cs-137 and Sr-90—were of any concern. So when I refer to “cesium” or “strontium” without any numbers, I have in mind cesium-137 and strontium-90.

Because of the plutonium-239 that fell closest to the reactor, the 10-kilometer zone will be uninhabitable for all imaginable time. The half-life of plutonium-239 is 24,110 years—about the same amount of time that has passed since modern humans first occupied Polissia during the last Ice Age. Thirty plutonium half-lives amount to a staggering 723,300 years.

“And how about radiation?” I asked Svitlana.

“Nature doesn’t notice radiation—not at these levels. At least not in a way that’s obvious to the eye,” she replied, sweeping her arm out to her side. “But all these plants are radioactive.”

In contrast to the radioactive releases in the civilian and military nuclear industries, Chernobyl was unique in the annals of radioecology not only in the magnitude of the release but also in the variety of physical and chemical forms that the release took. For example, during atmospheric testing, up to 90 percent of the radioactive cesium and strontium formed when the radionuclides that vaporized in the intense heat of the nuclear explosions condensed in cooler air. Such so-called condensates are water soluble and exchangeable, which are precisely the chemical forms that can be taken up into living things.

Chernobyl also released condensates, but they were light and were carried by the wind as far away as Ireland. Most of the contaminants that got dumped on the 30-kilometer zone were not condensates but radionuclides embedded in “hot particles”—insoluble bits of fuel, fission products, and radioactive graphite that were expelled from the reactor during the explosion and ranged in size from motes to chunks. In England, nearly all of the cesium was condensate. In the zone, nearly all of it was in hot particles. That’s why lessons learned about the health and environmental effects of nuclear weapons testing are not always relevant to Chernobyl.

Moreover, the other radionuclides spewed on to the zone were almost all embedded in hot particles—zirconium-95 and molybdenum-99, as well as several isotopes each of europium, neptunium, curium, americium, and plutonium. But because such elements don’t play a role in biology, not much of the precious government (domestic and

foreign) funding is allocated to researching their behavior in the wild. Nevertheless, a Ukrainian study in 2000 estimated that the zone contains 378 curies of europium-154, 194 curies of plutonium-238, 405 curies of plutonium-239 and 240, and 486 curies of americium-241. These are very large amounts. But it is worth comparing them to the figures for radiostrontium—20,790 curies and radiocesium—70,000!

During the early postdisaster period, all of that radioactive stuff was on the surface of things. Now after 18 years, 95 percent of all the radionuclides have sunk into the ground and from there some have made their way into plants. So, in contrast to the early postdisaster days, when nearly all plants’ exposure was from external sources of radiation, more than half of their exposure now is from radionuclides that they have incorporated internally.

Unlike external exposure, the impact of internal radiation depends on an enormous number of factors, including the types of radionuclides that are internalized, which determines whether the radiation emitted is alpha, beta, or gamma.

“Can we measure it?” asked Rimma, taking my dosimeter.

Svitlana flashed a white smile and shook her head. The botanist had bright blue eyes and, in contrast to the usual camouflage, wore a blue jacket to match them. My eyes are green with a touch of hazel and went well with the camouflage outfit I purchased at an army surplus shop in Kiev. In part, I did it to save the 15 dollars a day it cost to rent clothes from Chernobylinterinform. Mostly, though, I wanted clothes that fit me.

Actually, I could have worn any kind of clothes in the zone so long as I didn’t mind leaving them behind in the unlikely event that they got contaminated dust on them. But I quite liked my Chernobyl commando outfit and fancied that I resembled Linda Hamilton’s character in the movie Terminator 2: Judgment Day whose nuclear theme also seemed apt.

It is worth mentioning here the “lead suits” that many people believe provide the best protection against penetrating gamma radiation (alpha and beta particles are more easily blocked). I used to be one of them and once asked Rimma why there aren’t lead suits at Chernobyl. She reminded me that lead is very dense and heavy. Clothing could only have a very thin layer of the metal, otherwise it would be impossible to move. A layer that thin would block only about half of the

gamma rays and would nevertheless slow down your movements so much that you would increase your exposure just because you wouldn’t be able to dart in and out of the radioactive area quickly.

Rimma pointed the dosimeter near a wild plum. Adorned in its spring garb of white flowers, the tree’s thorns identified it as a wild—rather than abandoned—plum. Cultivated plum trees are usually unarmed.

“There’s no change in the reading,” she said with a puzzled frown.

“The dosimeter measures background radiation in the air,” Svitlana explained. “It tells you nothing about internal radiation. For cesium-137, you can determine internal contamination with gamma spectrometry. But for strontium, americium, and plutonium, you have to burn the sample and do a chemical analysis.”

Because it’s impossible to burn and analyze everything living in the zone, no one knows the exact amount of radionuclides that have gotten into the food chain, and estimates can vary considerably. But even these are dynamic figures. Life is not constant. Radionuclides are constantly flowing from one organism to another up the food chain and from one ecosystem to another.

Svitlana pulled a needle off a normal-looking pine sapling and absently rolled it between her fingers.

“We’ve studied radiation’s effects on pine trees the most because they’re so common here,” she said. “Their internal radioactivity fluctuates seasonally. It’s highest now, in the spring, because the trees’ juices are activating.”

Indeed, because the disaster happened in the spring, the plants’ fast growth promoted higher radionuclide uptake than if it had happened in the fall or winter.

Different trees favor different radionuclides. The Ukrainian zone’s populous pines contain more cesium than strontium. Birches have more strontium than cesium, as do spruce, oak, birch, and aspen.

But just because a radionuclide is in the ground doesn’t mean that it is bioavailable, or capable of being assimilated by living things. First of all, the nuclide must resemble something that organisms need. Plutonium, for example, imitates no atom of any use in biology and little of it gets into plants through their roots. Cesium, in contrast, is chemically similar to potassium, and strontium mimics calcium. Both are essential plant nutrients.

Potassium plays a role in synthesizing proteins, transporting sugar

molecules across cell membranes, and regulating how much water is lost on leaves. Calcium, among other things, affects the movement of chromosomes. So, when cesium-137 and strontium-90 chemically confuse plants into using them instead of the needed potassium and calcium, the radionuclides are shunted to those cells where calcium or potassium are needed at that time, exposing whatever biological molecules are nearby to highly localized beta and gamma radiation.

Light and fast, the beta particles emitted by cesium-137 and strontium-90 travel farther in tissue than alpha particles, traversing nearby cells and ionizing atoms along their path by knocking off electrons and breaking chemical bonds. Depending on where these atoms are and what they are doing in the cell, the results can range from harmless mischief, to cancerous mutation, to fatal damage.

Because they are so penetrating, gamma rays—emitted by cesium-137’s decay product barium-137—can do more distant damage than alpha and beta particles. But because living tissue—like most matter—is largely empty space at the atomic level, and gamma rays are subatomic in size, a lot of gamma radiation zips through without actually interacting with anything. What does, transfers its energy to subatomic particles such as electrons, which get very excited, breaking off whatever atom they were attached to and zapping around much like beta particles.

By 2003, nearly all of the external radiation bombarding us during our stroll comprised gamma rays, from barium-137 in the soil surface. But the gamma radiation decreases slightly each year as the cesium (and barium) decay.

Plants can’t take up all forms of cesium-137 and strontium-90. They can only absorb chemical nutrients as ions, which are positively or negatively charged “free” atoms, or as simple complexes, such as sodium chloride or table salt. Since living things are mostly water, the chemicals they need for nutrition must also be water soluble, like salt, which dissolves into sodium and chloride ions. Insoluble things don’t dissolve in water and can’t be absorbed.

This is why trees that grew on contaminated patches of Waterford, Ireland, in 1994 absorbed 13 times as much of the cesium deposited there as trees growing in Kopachi, in the 10-kilometer zone. Ireland was contaminated by condensed, water-soluble cesium carried large distances from the reactor. Kopachi’s cesium, in contrast, was mostly

in fuel particles. So, even though there was much more radiocesium in Kopachi soil than in Waterford, a smaller proportion got into the plants.

Although 95 percent of all radionuclides are believed to be in the upper layers of soil, bioavailable isotopes of cesium and strontium are more likely to be found in the zone’s living things. But strontium is more biologically active. While about one-fifth of the strontium is believed to be in zone vegetation, only about three percent of the cesium is thought to be.

Indeed, one of Chernobyl’s many surprising lessons is that just knowing how much radioactive cesium is in a given patch of land will tell you nothing about how much of it is in the vegetation growing there. This depends on whether the cesium is condensed or embedded in a hot particle and whether is it soluble or not. Soil quality also plays a critical role.

Radionuclides don’t sit still. They migrate, or move, from one place to another. Charts of cesium’s flow through an ecosystem are extraordinarily complex filigrees of knitted ties and connections. The nuclides often migrate with percolating water—which is how they get into plants—and the type of soil is largely what determines how much. Cesium gets into plants the most in peat lands.

Peat is made of dead sphagnum moss that has not fully decomposed because the environments in which the mosses grow are low in nutrients, oxygen, and the bacteria responsible for decay. Waterlogged peat lands, called mires, form either bogs or fens. A bog is fed almost exclusively by rainfall and other forms of atmospheric precipitation. It is very low in nutrients and supports few species of plants, such as sphagnum mosses as well as carnivorous plants that must get their nutrients from insects. Things that fall into bogs barely decompose, which is why there is an entire subdiscipline of archaeology devoted to bogs. A fen, in contrast, is fed by groundwater and river flooding. Because it is richer in nutrients, sedges, reeds, and many other plants grow in its shallow waters.

Cesium is very mobile in mires because the partly decomposed dead moss that is peat’s primary ingredient retains water and the cesium keeps floating around. Floating cesium is generally soluble cesium—precisely the kind that gets taken up by plant roots. Also, peat soils are acidic, which also makes cesium more water soluble. This explains why the Kiev region of central Ukraine is more contaminated

with cesium, but plants growing on the drained, acidic peat lands found in parts of the Polissia region incorporate more of the radionuclides internally.

Indeed, it became clear after atmospheric nuclear testing in the mid-1960s that Polissia was absolutely anomalous when it came to radionuclide mobility up the food chain and into people. Given the same levels of soil contamination after global testing, a person living in Polissia absorbed 10 times as much radioactivity as a person living in Moscow or Minsk—all because of the type of soil there.

Cesium migrates the least in soils with a lot of clay because the minuscule clay particles are very sticky and the cesium gets glued to them, becoming increasingly biounavailable with time.

Or so, at least, it was thought. It may be that the cesium is being fixed by bacteria rather than clay. Some species of bacteria have such a huge appetite for cesium—any kind, radioactive or not—that their ability to incorporate the stuff is comparable to laboratory materials specially developed to separate cesium from other elements. Moreover, the cesium-eating strains can be found anywhere their favorite food is. Samples of the microbes taken from close to the ruined No. 4 reactor are almost as radioactive as nuclear fuel. The bacteria hold promise in radiological cleanup, although such applications require a good deal of work. For one thing, when they are on surfaces, the bacteria are basically indistinguishable from dust, so they can spread radioactivity as well as fix it.

Thus far, however, no one has identified strontium-eating bacteria. In fact, strontium doesn’t fix onto much of anything in soil. In contrast to cesium-137, the amount of water-soluble strontium-90 in the root level of a given patch of soil is a pretty good measure of how much strontium will be in the plants growing there. Unlike cesium, whose absorption by plants was stabilizing after 15 years, the amounts of strontium continued to grow.

July 6 is a magical date in Ukrainian folklore. Popularly called the Eve of Ivan Kupala—which is a merging of St. John’s (or Ivan’s) Day in the Orthodox Church calendar with Kupala, the name of a pagan Slavic fertility godlet—it is a night when the sun was said to bathe by dipping into waters on the horizon, imbuing streams and lakes with special

charms. A wreath cast into their currents will presage a maiden’s marital prospects. Herbs gathered before sunset are especially powerful, while at night all plants are able to walk and talk. It is also a dangerous night, when sundry demons and sprites prowl for human victims. Considered especially dangerous were the rusalkas, water nymphs, whose fear of wormwood prompted the superstitious to hang sprigs of the weed on their cottages and outbuildings. Even Soviet disapproval couldn’t entirely eliminate the folk customs, including the charming Polissian spring ritual of “banishing the rusalkas,” in which a girl or female effigy was ritually buried in a field by a river, symbolizing an annual cleansing of the evil spirits. But rusalkas revived their powers in the magical waters of Ivan Kupala.

Actually, I had never understood why rusalkas were believed to pose a problem in a region where wormwood has been common since the Ice Age and the largest town—Chornobyl—was named after the plant (for folklore purposes, Artemisia vulgaris and A. absinthium were both effective rusalkas repellants). But in a feral meadow of parched yellow grasses, blooming wildflowers, and the occasional Artemisia specimen in the southern quadrant of the 10-kilometer zone, I mused that perhaps rusalkas sought revenge for the gradual destruction of their woodland habitat. The field I was in had been forested for millennia, but it was leveled for lumber in the nineteenth century and in Soviet times became a potato farm. Before 1986 it would have been cleared of any vegetation that was not potato—including wormwood—and Artemisia’s absence made the land vulnerable to the dangerous nymphs. Now that nuclear wormwood from Chernobyl has put an end to cultivation, the landscape is returning to its natural state and the repellant plants have been able to return, once again making the zone a rusalkas-free habitat.

Such whimsical thoughts occurred to me as I followed Rimma and Svitlana the botanist on a short hike in Cherevach, an abandoned village on a floodplain of the Uzh River. The dirt path that led from the main road into the village wasn’t much of a road. In fact, it wasn’t a road at all. After about 20 feet, it ended abruptly in a sea of deep grasses and shrubs.

Ivan Kupala was a warm and dry day with a light wind, but the air was sweet from the previous night’s rain. Parched conditions were precisely right for stirring up radioactive dust. Radiation readings are always slightly higher on dry, windy days.

Cherevach was on a dark-beige patch on the cesium maps, meaning it was only moderately contaminated with that radionuclide, although its strontium-90 concentrations were among the highest in the zone.

Ninety percent of the strontium that fell in the Ukrainian zone was embedded in the insoluble hot particles that have sunk into the top layers of soil over 18 years. There is less field research in Belarus than in Ukraine, although only about half the strontium there is thought to be in the fuel particles. Because they are insoluble, hot particles sink by mechanical mixing and migrate much more slowly than the condensed cesium and strontium that flow with percolating water and have sunk more deeply.

Strontium in a hot particle becomes bioavailable only when the particle dissolves. So the particles are like a line that prevents radionuclides from getting into the food chain. The soil largely determines how quickly hot particles dissolve—the more acidic the soil, the faster the disintegration. Given the variety of zone soils—sandy, peaty, podzolic—disintegration has been very uneven, although it was relatively rapid in the acidic podzol beneath our feet. Podzolic soils are formed by forests that grow on the deposits left by melting glaciers. Because it is acidic and has very little organic matter, podzolic soil is not fertile.

At first it was believed that all of the particles were bits of uranium oxide fuel, most of which would dissolve after 15 years and release the maximum amounts of strontium in 2006. By then a good part of the nuclides will have decayed, so the total amount of it released from the particles will be only about a fifth of the amount of “free” strontium in 2001.

But it may be that things are more complicated. Scientists who scanned Red Forest fuel particles with an electron microscope found that there were actually three types of particles. The first group comprised bits of uranium oxide that broke out from the reactor core in the explosion, the second was made up of bits of uranium oxide that burned in the graphite fire before being thrown from the reactor, and the third group was made of bits of uranium oxide that had not burned in the graphite fire but instead had melted together with some of the zirconium from the fuel rods.

Although the burned bits of fuel were the least stable—dissolving easily—and the unburned uranium oxide was quite stable, the scientists were surprised to find that the zirconium particles were

superstable. Since nearly all of the zone’s strontium is in various kinds of fuel particles, the fact that not all of the particles dissolve very easily means that the amount of strontium that will eventually become bioavailable may be less than previously thought.

For more than a decade after the disaster, scientists had only a vague idea about how much strontium there was. The isotope emits no gamma rays, and its relatively low-energy beta particle doesn’t help identify it. First of all, beta radiation is stopped by solid materials, and if the beta’s source is in the soil, there are plenty of solids there to stop much of it from reaching the surface. Even if a beta particle got through, however, you wouldn’t know if it was from strontium-90 or from a natural beta emitter such as carbon-14 or potassium-40. Unlike alpha particles, which have the same energy for any given isotope, beta particles have a range of energies up to a certain maximum. The only way of knowing how much strontium-90 is in something is to do expensive, laborious, and time-consuming reactions to separate the isotope from other elements and then, finally, measure its beta decay.

A Belarusian scientist once told me that doing strontium chemistry was “women’s work” compared to cesium. Cesium chemistry merely involved putting a sample into a machine, which measured the gamma radiation of its decay product barium-137 and popped out an answer. In contrast, just separating strontium from whatever matrix it is in requires a great deal of mixing, heating, centrifuging, and adding ingredients—all done in a beaker on a stove, just like a “hausfrau” laboring over dinner.

Mapping the zone’s strontium required doing that many times with many samples taken from many places. When Ukraine finally did this in 1997, scientists concluded that most of the Chernobyl strontium was condensed and had floated beyond the zone’s borders. As for the hot particles that fell within its borders, they were very unevenly distributed. Nearly 80 percent are concentrated on one-tenth of the territory.

The profuse grasses were incredibly thick, and our walking stirred up a variety of insects that flew up my nose and stuck to my sunglasses. Swarms of mosquitoes bit imperviously through the OFF I had smeared on my body and sprayed on my clothes before setting out. Polissia’s summer landscapes were picturesque, but the mosquitoes were punishing. I slapped them, wondering if they were radioactive

and, if so, was every dead mosquito on my skin leaving a patch of contamination. But Svitlana was a botanist and confessed to knowing nothing about mosquitoes.

Rimma was scouting up ahead with my dosimeter and calling out radiation levels. We were on a berry hunt, but it seemed none of us were very good at it. A patch of huckleberries we found hadn’t ripened yet.

“We need to find an old garden or something,” said Svitlana. Though berries grew wild in the forests, most Polissians also planted them in their gardens for easy access. “Raspberries and blueberries should already be ripe.”

The trouble was we couldn’t find any. We weren’t looking for berries to eat them. In fact, the first sign you see upon entering the 30-kilometer zone is a large billboard explaining that open fires, hunting and fishing, and wild mushroom and berry picking are forbidden. I wanted to find some berries and then take them to a lab for strontium testing but making that a part of this story wasn’t looking very promising.

I asked Svitlana why berries are such magnets for radionuclides.

“Berries are usually shrubs or herbaceous plants,” she explained. “They have relatively shallow roots that penetrate into the layers of soil with the highest concentrations of radionuclides. The root hairs that absorb inorganic ions like calcium and potassium are especially concentrated in those levels. Plus, berries are reproductive tissues and all reproductive tissues concentrate nutrients—as well as the radionuclides that imitate them.”

A similar principle applies to grasses, which also have shallow root systems. But people don’t eat grass. They do eat berries. (They also eat the game animals that eat grass and berries.)

I was hoping to find currants, which are especially radioactive. But instead of currants, we found some dark green sorrel growing amid the dry grasses. Like all leafy vegetables, sorrel was a good source of calcium—and, in zone sorrel, strontium. But although strontium chemically mimics calcium and plants metabolize them in similar ways, cell membranes distinguish between them. Given access to both calcium and strontium, living things will preferably absorb the real nutrient. They will also select potassium over cesium. That is why fertilizing cultivated fields with potassium and calcium decreases the plants’ up-

take of radionuclides. But no one had fertilized the zone for nearly two decades.

Unlike potassium—and its imitator radiocesium—which both peak in the spring and then decrease, calcium and radiostrontium are stored by plants, which start accumulating the mineral in summer and continue to do so throughout the growing season.

“That’s why you find more strontium in older plant tissues at the end of the growing season, in the fall,” said Svitlana. “In pine for example, young needles contain more cesium than strontium, while the older ones have more strontium than cesium.”

Another reason for this is that calcium (and strontium) are not very mobile in plants. Unlike potassium (or cesium), which can get transferred from place to place as needed by the plant’s circulatory system, calcium (or strontium) stays put.

Rimma peered into the distance through a cloud of mosquitoes that hung in the air and announced that she saw what looked like an abandoned yard. She went ahead of us to reconnoiter and shouted out radiation readings that were double and triple natural background.

“Even if there are some berries left, it’s unlikely we’ll be able to see them in this deep grass,” Svitlana said, brushing a black bug off her check.

I called out to Rimma who seemed to have disappeared into the thicket. But she emerged quickly, explaining that she had gone to take a closer look at what looked like raspberries only to find nettles instead.

It was a fool’s errand to look for berries while tramping through a carpet of grass that was so thick it was like walking through deep snow. Svitlana pointed to the thatch—the deep, tightly tangled layer of living and dead stems, leaves, and roots that had accumulated between the layer of actively growing grass and the soil. She dug at it with her heel to expose some of the more rotten layers beneath the surface but didn’t come even close to exposing the ground beneath. The thatch must have been about a foot thick.

“Radionuclides are less fixed in natural meadows and pastures than in cultivated fields because they accumulate in the thatch and remain bioavailable,” she explained.

As a variety of invertebrates, fungi, and microorganisms decompose the thatch, the radionuclides locked inside the plants return to the soil. In plowed fields, thatch never has a chance to build up in the first place.

Understanding many of the “hows” and “whys” of radioecology will take many decades. One problem is money. Neither Ukraine nor Belarus has much of it for research at a time of budgetary shortfalls for even basic safety works in the zone, while international funding has tapered off significantly since the 1990s. Chernobyl has yet to generate more than sporadic science despite high hopes in the immediate aftermath of the disaster, which some scientists referred to as the world’s largest field experiment in radiology.

Indeed, when Chernobyl exploded in 1986, American scientists knew exactly as much as they had known in 1976 about radiology because in the early 1970s the U.S. government cut research funding. Studies that started in the 1950s and 1960s and were designed to be long term were cut. But even those studies were usually laboratory experiments where a gamma radiation source was stuck in some area and scientists studied its effects on the surroundings. There were very few studies of the effects of fallout, and little was known about the effects of beta radiation.

Actually, it is more accurate to say that whatever was known was known to only a few. The Soviets had done radioecology studies after nuclear spills in their nuclear weapons industry. But these were super-secret and unpublished—a good deal remains classified. When those scientists came to the Chernobyl zone immediately after the disaster, they already knew much that was new to civilian scientists.

Chernobyl provided a unique opportunity to openly study all that and more, but it won’t last forever. With biologically active radionuclides such as strontium and cesium constantly decaying, the window for studying high levels of contamination in the environment will eventually close. At the same time, Chernobyl’s long-lived radionuclides such as plutonium and americium will continue to affect living things for a very, very long time to come.

The very fact that vegetation is thriving in the zone means that plants can adapt to living in a radioactive environment. But the plants are under evolutionary stress and intense natural selection. The result could be a selection for genes that are highly adaptive to stress, that could eventually be used in producing transgenic plants. But more time and study (as well as money) will be needed.

The zone’s very uniqueness also poses a problem. If its plant life is considered part of a giant field experiment to observe the impact of radiation on natural habitats, then the zone plants should be com-

pared with controls. But finding exactly the same plants growing in exactly the same conditions—except without radiation—is more easily said than done for the simple reason that every part of the Earth’s surface is unique. There cannot be any other place like it on the planet if only because no other place can have the same geographical coordinates—to say nothing of the properties of soil (such as the anomalous ability of Polissia soils to transfer radionuclides into the food chain), air, water, sunlight, and myriad other variables that make up a particular habitat.

The October day was bright and crisp as an apple, illuminating the scarlet, umber, and gold foliage that still clung to the trees after heavy rains a week earlier. The carpet of forest litter had dried on the surface but was still damp beneath, crunching and squishing beneath my feet as I hiked through a forest just three miles from the reactor complex.

I was tagging along with two dozen Chernobyl explorers—a multigenerational and enthusiastic crew of ethnographers, radiologists, chemists, and biologists sponsored by the Ukrainian Ministry of Emergencies. Their job was to collect, codify, and preserve the cultural artifacts left in the zone after its evacuation.

The only odd note was the armed policeman in a flak jacket.

“He’s for protection,” said Yaroslav Taras, an architect with salt-and-pepper hair who had appointed himself my escort and explainer. “There are outlaws who live in the abandoned villages, poachers, looters. There are hundreds of thousands of tons of abandoned radioactive machinery that people steal to sell as scrap metal.”

With most of the 340 police and firefighters concentrated on the Ukrainian zone’s perimeter, at the nuclear plant, and in the town of Chornobyl, vast regions are essentially lawless.

I thought of the barrows of Burakivka and all the contaminated waste that was just littered around the zone, waiting to be buried and pretty much free for the taking. The only problem was getting it past the checkpoints. In a poor and corrupt country like Ukraine, checkpoints are often merely a negotiating tool—although the Chernobyl checkpoints are tougher than most.

We were on the outskirts of an abandoned village called Novoshepelychi, a deep mauve patch on the radiation maps, and in the

depths of an old forest whose border had been ringed with young pines. Trees, it turns out, are the best and cheapest way of fixing radionuclides because they stay put and decay away in the decades and centuries of a tree’s lifetime.

Radioactive atoms generally target physiologically active tissues such as the cells responsible for photosynthesis in leaves and needles. A good portion of radionuclides are also in the bark. Since bark is not metabolically active, it may be because the contamination is external, from radionuclides kicked up into dust by the wind. With each annual layer of bark, older layers become trunk wood but, oddly enough, the nuclides are very mobile in wood and don’t stay in it very long. The 1986 tree rings, which were bark in 1986 and coated with fallout, don’t display the highest contamination levels. These are invariably in the cambium—the trees’ circulation organ.

Once radionuclides are fixed in trees, the greatest danger in the wormwood forests becomes fire, like the 1992 blaze that consumed 30,000 acres (12,000 hectares) of forest and caused pockets of panic in Kiev. Burning breaks the chemical bonds locking radionuclides into biological molecules and resuspends them into the air much like the original Chernobyl fallout, although they don’t drift very far. The main radiological danger is to firefighters, who risk inhaling plutonium.

For years, members of the expedition had been searching for the Novoshepelychi graveyard, but it was hidden so deeply in the forest that they hadn’t been able to find it. But this time they had a guide, a stocky bus driver who grew up in the village.

The policeman in front with the bus driver, we walked swiftly up the path until we came upon the gravestones and metal crosses that seemed to grow out of the forest. The brittle whisper of falling leaves surrounded me as I tramped through the thick underbrush, my dosimeter hovering around a rather high hourly reading of 100 microroentgens.

When he saw me staring at the liquid crystal screen, Taras said: “Graveyards have higher radiation because the Polissians always put them on higher elevations, which caught more of the fallout. They knew that if the bodies were buried on lowlands, they would pollute the groundwater because it is so close to the surface in the swamps.”

Zone cemeteries also have higher radiation levels because they are in forests and the trees are so big that they lock up a great deal of radioactivity. Of all zone workers, aside from those working with ra-

dioactive waste and those working close to the ruined reactor, forest rangers get among the highest occupational doses. In the early years, this was because radioactive grime coated the trees along their length, especially their crowns. In those days, the radiation dose actually increased the higher you went.

After a decade, one reason for the rangers’ high exposure levels is banal—forest rangers are among the zone’s most notorious poachers, and they also forage for mushrooms and berries—all of which contribute to their high average internal radioactivity levels. Another reason is that the forest floor is among the most radioactive parts of the zone environment.

Trees aren’t the only forest vegetation to lock up radionuclides. Mosses are also culprits because, unlike vascular plants, they lack true roots and get most of their nutrients—and the radionuclides that mimic them—from the air. So, when wind kicks up radioactive dust or rain washes it off, mosses absorb the radionuclides easily. In 2001 a kilogram of some moss samples contained 90,000 becquerels.

The radioactive leaves that had been high in the air in spring and summer had fallen to the ground. While the expedition bushwhacked into the brush to videotape, photograph, and take notes on the gravestones, I made my way to an old oak surrounded by fallen leaves, many of them covered with galls. Most galls are formed by tiny dark wasps called cynipids, or gall wasps, which lay their eggs on different plants (each cynipid species prefers a different species of plant). The larvae release substances that cause the plant to grow extra tissue, some spherical and as large as golf balls, that serves the larvae as a nursery and pantry while they develop.

But some galls are symptoms of crown gall disease. This is caused by Agrobacterium tumefaciens, a bacterium that actually transfers a part of its DNA to the plant, which integrates it into its genome. In crown gall disease, this leads to the production of tumor-like growths that are the closest things to cancer in plants, although the growths usually don’t harm mature plants. In plant breeding and genetic engineering, however, A. tumefaciens is widely used to insert useful genes such as those for herbicide resistance into plant genomes. Even under low radiation doses, the incidence of crown gall disease in the zone is much higher than outside, and the galls are much larger as well. This may be because radiation damages the plants’ ability to recognize the crown gall bacterium and fight it.

Near the fence of an infant-sized grave marked with a tiny cross of welded metal, I kicked over a stand of mushrooms and dug through the forest litter with my heel, releasing a waft of fungal damp. It was a warm October, warm enough for nature’s sundry sanitation workers to still be active. Centipedes quickly snaked away from the light and disappeared into the dark fragments of chewed-up litter from years past. Worms wriggled iridescently and millipedes rolled up into small pills protected by black armor.

The first layer of forest soil, known as the “O” or “organic” layer, is the recycling factory where decomposition releases the nutrients in dead forest products and makes them available for reuse. In Chernobyl forests, the O layer is the key to unlocking radionuclides.

The organic layer is made up of three easily distinguishable horizons. The top layer, called “Ol” for “organic litter,” was the layer of freshly fallen leaves, twigs, branches, bark, flowers, fruits, and other botanical detritus that I was walking on. The “f” in the “Of” layer refers to the “fragments” of dark, partly decomposed plant debris beneath the fresh litter. The final layer was made of the amorphous and fully decomposed organic gook that is the prize at the bottom of backyard compost piles and the stuff that gives Ukraine’s black earth its famous fertility. It is called “Oh,” with the “h” standing for “humus.”

The denizens of the decomposition from litter to humus are so sundry and numerous that science has yet to even count them all. For every creepy crawly I could see with my eyes, there were thousands more visible only under microscopes. In the first decade after the disaster, however, species diversity declined by more than half, probably because the forest litter was so highly radioactive. There were fewer ticks, millipedes, and other invertebrates in forest soil than outside the zone. But the populations have been rebounding in the second decade, perhaps because radiation levels have fallen or because the insects are developing resistance. Adult insects, as a rule, are highly radioresistant.

From teensy mites to even tinier bacteria and certain kinds of fungi, an astonishingly diverse and largely unknown world was at work. Indeed, so little is known about the microbial world that no one has ever documented the extinction of a single bacterium! Given such mysteries, it is impossible to know all of the pathways by which radionuclides migrate through the seasonal cycles of an ecosystem. But decades of study at other nuclear spills have mapped the basic mechanism, and

18 years of Chernobyl studies have revealed much more and suggested some promising avenues for research.

Along with bacteria, fungi are nature’s principal decomposers, and they may play a surprising role in the movement of radionuclides through the environment. Occupying their own kingdom between animals and plants—though they are closer to animals than to green plants—the total number of fungi species may run as high as 1.5 million or more. But mycologists—or fungi experts—can’t agree on this, or on the number that have formally been described, a figure that ranges from 74,000 to 300,000. And those that have been identified are hard to generalize. Some fungi, such as yeast, are single-celled. The rest are composed of filaments called hyphae that form a mass called a mycelium. The thread-like hyphae are so small that they can grow right through seemingly solid objects. Fungi don’t ingest nutrients. They ooze enzymes onto wood, toenails, or some other substrate and then absorb the simple sugars and amino acids that are released.

Although we see only a part of them, fungi are such an integral part of the forest that if you removed all of the trees and soil and just left the fungi behind, you’d still be able to see the outlines of trees and soil.

As the mycelium webs out in the ground, no part of it is more than a few micrometers from the environment. When rain percolates through it, the fungal web acts as a filter, absorbing nutrients and water. In the zone, of course, the word “nutrients” should always raise red flags for the radionuclides that mimic them, and the mycelium’s role as a nutrient sponge may explain one experiment in which the amounts of radioactive cesium in the Ol layer periodically increased even as the total amounts of litter decreased.

Forest soil and litter are, in general, very radioactive. There is more cesium in forest litter than in all other elements of wild flora. This is because the litter is made up of leaves and needles that bore the brunt of the 1986 fallout as well as fresh leaves—which also take up radionuclides—that fall each season. Since the concentrations of nutrients increase as organic litter decomposes to humus, so do concentrations of the radionuclides that mimic them. This is one reason the fragment and humus layers contain about a quarter more cesium than the fresh litter. Another reason is that nearly all of the zone’s radionuclides are in the top two inches of soil, where the Of and Oh layers are located and also where fungal mycelia are found.

When fresh leaves fall, some fungal mycelia will grow their way into the new litter. If they have accumulated cesium from the Of and Oh layers, they will also import the radionuclide to Ol, increasing the concentration of cesium even as the total amounts of litter decrease. Since mycelia can also cover a very large area—some fungi are the largest living things on Earth—it may be that they can shunt cesium from far distances. At least this is one theory to explain the strange experimental results.

Nevertheless, fungi’s role in the circulation of radioactive cesium is not well understood. One reason is that mycology is not exactly “sexy” science. The dank association of mushrooms with witchcraft, damp, and decay doesn’t attract many young scientists. Radioactive mushrooms hold still less appeal.

The intimate relationship between fungal mycelia and the cesium-rich organic layers of the forest floor also explains why mushrooms contain more cesium-137 than any other forest vegetation. One of the highest concentrations ever was found in a highly poisonous naked brimcap (Paxillus involutus) growing on peaty soils 28 miles from the plant.

Mushrooms, in general, are highly contaminated. But much depends on the species and how deeply the main part of their mycelium penetrates the soil to layers where cesium is concentrated. For years after the disaster, mushrooms such as bay boletus (Boletus badius)—whose shallow mycelia don’t penetrate past the humus layer—contained 10 times as much cesium as porcini mushrooms—whose mycelia penetrate past the humus into the mineral layers of soil. In 1997 a bay boletus mushroom found in the buried village of Yaniv, not far from the nuclear station, contained an astonishing 2 million becquerels of radiocesium per kilogram.

In Ukraine the maximum amount of cesium allowed in a kilogram of mushrooms is 500 becquerels.

Since 2000, however, shallow species like bay boletus have been decreasing their cesium uptake, while penetrating species such as porcini have been increasing it. In 2001 a bay boletus in Yaniv contained about 500,000 becquerels per kilogram and a porcini contained 160,000. Two years later, a kilo of Yaniv porcinis contained 500,000 becquerels of cesium, while the same amount of bay boletus contained only half as much.

Moreover, the amounts of strontium-90 in mushrooms have been

increasing since 1996. In part, this has been a result of the disintegration of fuel particles, a process that is also aided by fungi. Strontium is much more dangerous to human health than cesium because it concentrates in bones, where its beta particles can damage bone marrow. It also has very low biological turnover. Whatever strontium you absorb stays in your body for years.

But even as porcinis’ radioactivity levels are expected to continue increasing in the coming years, they don’t win the dubious prize for cesium concentrations. This belongs to naked brimcaps, which contain 10 times as much cesium. But naked brimcaps are poisonous, and porcinis are highly prized by Polissian mushroom hunters.

The mushrooms growing around the graves in the cemetery were like the apples on a subterranean mycelium tree, bearing spores that are the fungal equivalent of seeds—except that the tree was huge, like a dense underground spider web that could extend for many square miles, so that the mushrooms I kicked over in Novoshepelychi might be siblings of mushrooms growing four miles to the west in Kopachi or four miles to the north in a patch of Belarusian forest.

It was hard to believe that Belarus was so close. Indeed, being in the Ukrainian part of the exclusion zone made it easy to forget that there is an entirely “foreign” part of the zone in a different country. And whenever I did remember, I simply thought that Belarus’s zone was much like Ukraine’s.

Until I went there.

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