Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
SAF Archives  search ask the scientists in the classroom cool science
scientists from previous shows
cool careers in science
ask the scientists
PREVIOUS SCIENTISTS

Photo of Birgitta Ahman Radioactive Reindeer -- Birgitta Ahman

After the nuclear explosion at Chernobyl in 1986, fallout contaminated Lapland, home of the Sami people and their reindeer herds. Birgitta Ahman of the Reindeer Husbandry Unit at the Swedish University of Agricultural Sciences responded to questions about radioactivity and reindeer.



QDo you ever get worried about handling the reindeer? Are there health risks associated with being in close contact with them, such as leukemia?

There is very little extra radiation connected with handling the reindeer. The main part of the radiation dose to humans, caused by the Chernobyl fallout, comes from eating foods, e.g. reindeer meat, contaminated with radiocesium. The cesium is being absorbed by the tissues of the body (and also eventually excreted) resulting in an increased internal radiation dose. This extra dose may cause cancer, though the risk is marginal compared to getting cancer for other reasons. However, because of this risk, reindeer owners in the most contaminated areas are advised either to eat meat from reindeer slaughtered in the fall, when the animals have been grazing less contaminated pasture (as grass and herbs), or to feed the reindeer uncontaminated feed during some period before they are slaughtered (by 2 month feeding, the radiocesium levels in the muscles, meat, of the reindeer is decreased to 10 to 15 percent of the initial content).

A smaller part of the radiation comes from outside the body, external radiation. In a reindeer corral with several hundred reindeer, the external radiation could be two or three times higher than in the surroundings. The time spent in the corral is, however, limited and since the radiation dose, and the possible damage, to your body is a product of the intensity of the radiation and the time, the handling of reindeer could not be considered as an extra risk, with respect to radiation.

I wondered whether the lichen that apparently are the primary source of radioactive contamination for the reindeer, and the people, are still absorbing radioactive fallout from the air or if the absorption only dates from the Chernobyl accident? How long does lichen live and how long can we expect it will stay contaminated? Does the lichen transmit other contaminates from the air?

Almost all the radioactive contamination from Chernobyl reached the ground within a few days in 1986 and was absorbed by the lichens at this time.

There is some contamination left also from nuclear bomb tests made 30-40 years ago (in contrast to the Chernobyl fallout, this contamination was released high in the atmosphere causing fallout during several years).

Lichens grow slowly and live very long. Reindeer lichens grow from the top and die from the bottom so it is hard to say how long they actually live. The levels of radiocesium in lichens seem to have decreased by about 15 percent each year since the Chernobyl accident. This is reflected in the reindeer, which now (1998) have radiocesium levels in the winter that are about 20 percent of the levels measured during the first winter after the accident (1986/87).

Lichens also absorb other contaminates, e.g., heavy metals, from air and precipitation and enhanced levels of lead and cadmium have been observed in the liver and kidneys of older reindeer.



Q Has the radioactive lichen affected other animals or ecosystems?

Lichens are eaten mainly by reindeer and contamination of lichens has probably not directly affected animals other than reindeer. Contamination of reindeer, however, result in high levels of radiocesium in predators (lynx, wolverine, wolf).

The fallout affected other ecosystems. Most vegetation naturally occurring in the forest ecosystem absorbs more or less radiocesium through their roots. High levels of radiocesium has been recorded, e.g., in moose and roe-deer. Lakes were also contaminated and fresh water fish, specially those high in the food chain (fishes eating other fishes that, in turn, eat other fishes etc.).

The radiation doses in Sweden from the Chernobyl are relatively low and it is not possible to see any visible health effects or changes in animals or vegetation.



Q How much longer will it take for the reindeer to get back to normal?

It will probably take about 30 more years before the radiocesium levels of reindeer are on the same level as before Chernobyl in all areas. However, each year less of the reindeer herding area is subjected to special measures.



Q Why were the reindeer not radioactive before they ate the lichens if they were exposed to the same amount of radiation as the lichens?

The reindeer (or lichens) do not get radioactive by being subjected to radiation (ionizing radiation does NOT make things radioactive) but by absorbing material that is radioactive (like cesium-137). Lichens can absorb material (like cesium) from the air and rain and get contaminated in this way. Reindeer do not absorb cesium from air but by eating lichens or other vegetation that contain radioactive cesium.



Q How have the Sami people survived if their chief source of money and food (the reindeer) cannot be eaten or sold?

The reindeer herders have been refunded from the Swedish government for costs for countermeasures (like feeding the reindeer "clean" food) and for loss of income because of the radioactive fallout.



Q We saw you using a hand-held radiation detector. Can you please tell us a little about how it works?

The detector contains a Sodium-Iodine crystal that is affected by ionizing radiation (gamma-radiation) coming from the radioactive cesium. The changes in the crystal can be converted into electrical pulses and measured in this way.



Q Does a low level of radioactive contamination cause the reindeer to have a shortened life span? Or any genetic defects in offspring?

There is a possibility that single reindeer could have, for example, gotten cancer tumors from the radiation and died from these. However, the possible cases are too few to be detected among all other causes of death and have not increased the losses of reindeer. There is one investigation showing some indication of a change in the genetic material of reindeer calves born during the spring of the fallout. The indications are weak, however, and have not been confirmed by other investigations.



Q Should tourists or visitors be concerned about visiting Sweden or other areas near there because of the radioactivity remaining from the explosion of the nuclear power plant in Russia many years ago

NO! There is no need to be concerned about visiting Sweden or any other country affected by the Chernobyl accident because of possible extra radiation dose. There has been no measurable health effect even among the people that have been living in Sweden during the now soon 12 years that have passed since the accident.

The average increase of radiation dose for Swedish people because of Chernobyl is around 1 mSv in a lifetime (50 years) - that is 0.02 mSv (millisievert) per year (0.0004 mSv per week to a person visiting Sweden for one week). This should be compared to the natural radiation dose that all persons, also in USA, receive from natural sources throughout their lives. The natural dose is normally 0.4-4.0 mSv per year depending on where these persons live (depending on radon gas in the ground or, for example, that the cosmic radiation is higher at higher altitudes).

It might seem strange that there is so much concern about the Chernobyl accident when the increase in radiation dose and the corresponding health risks are so minimal. However, the concern is mainly for those (relatively few) people, as reindeer herders or hunters, that eat reindeer meat or game meat almost every day for their whole life and therefore may increase their radiation dose significantly.



Q Can reindeer pass their radioactivity to their calves when they are born, or is it just passed by the foods they eat that contain radiocesium?

Radioactive cesium will pass from the mother to the fetus, and via milk from the mother to the calf after birth. However, cesium is excreted from the body and if the calf eats "clean" food later it will get rid of its cesium.



Q You said the first year 80% of the reindeer had to be killed. How many of them need to be killed now?

Last year (1997) about 1% of the slaughtered reindeer in Sweden were destroyed because of high cesium levels.



Q How does the radiation cause diseases such as cancer in the reindeer and in people?

Ionising radiation, as this is, can change the structure of most molecules at a certain risk, depending on the intensity of the radiation. It can therefore also change the structure of the genetic material in living cells. The cells have systems for reparation and many "injuries" are repaired by the cell itself.

If the injury is bad, then the cell often dies and no harm is really done - provided the intensity of the radiation is not so high that it kills very many cells at the same time (e.g. intense local radiation on the skin can cause a sort of burn).

In unlucky cases, however, the genetic material may be changed so that the cell goes on living but has damage in its genetic material making it into a cancer cell that can grow into a tumor.




 

Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.