FROM the height of an orbiting satellite to the bottom of the sea, there are small repositories of nuclear waste whose potential to pollute our environment has largely gone unnoticed. This out-of-sight, out-of-mind hazard is hardly in the same league as the Chernobyl accident. Yet its quiet growth is disturbing. What began as an insignificant environmental threat now seems on the verge of getting out of hand.
According to a study by the Teledyne Brown company in Colorado, there's a little over a ton of highly enriched uranium, plutonium, and various radioactive fission products circling Earth on board several dozen United States and Soviet satellites. Some of it is in small nuclear reactors. The rest is in so-called atomic batteries that turn the heat of decaying radioactive elements into electricity. There could be more than three tons of this stuff in orbit by the year 2000.
Many of these atom-powered satellites are ``parked'' in orbits where they should stay for hundreds of years. But, as their numbers grow, the possibility of collision among them increases. The resulting debris could soon find its way to lower orbits to menace astronauts, cosmonauts, and unmanned satellites alike.
A few such satellites have already returned from orbit or dropped back after launch failures. One contaminated parts of Canada nine years ago (see photo). Others lie corroding at the bottom of the sea.
Meanwhile, Britain's Sellafield nuclear fuel reprocessing and reactor site has built up a different kind of radioactive pollution source on the Irish Sea bed. It's an environmental hazard that will increase in severity for decades even if the discharges were stopped tomorrow.
Sellafield's pollution began in the early 1950s, peaked in the early 1970s, and now is being sharply curtailed. However, to quote a report issued last January by Britain's House of Commons Environment Committee, it has already made the Irish Sea ``the most radioactive sea in the world.''
This has been well publicized. What has not been widely appreciated is the extent to which the environmental threat due to radio-elements trapped in seabed sediments will remain.
Plutonium absorbed there decays into the element americium, which emits a more dangerous form of radiation than does the original plutonium.
As noted in a survey of Sellafield pollution in the current issue of Oceanus, published by the Woods Hole Oceanographic Institution, the rate of alpha radiation will continue to build up in these sediments for many decades even if there is no new contamination.
Experts still don't understand all the ways this radioactivity can reach people. They've traced contamination through seafood and in sediment particles swept onto beaches. But new subtle routes continue to be found. Last month, for example, a research team from the University of East Anglia and the United Kingdom Atomic Energy Authority Harwell Laboratory reported that sediment particles are carried up through the water and shot into the air by bursting bubbles.
They explain in the paper published in Nature that the concentration of radioactive elements in the air is between 30 and 600 times what it is in the water.
All of this involves very low levels of radiation. Neither the Sellafield discharges, nor similar discharges from a few other seaside nuclear facilities, nor the atom-powered satellites have yet caused any significant health hazards as far as is known.
Yet they represent a growing, little-known, and uncontrollable store of radioactive material that is slowly building up in inaccessible parts of Earth's environment. The people who originally planned the relevant operations failed to take this into account.
The Chernobyl reactor disaster focused world attention on nuclear safety. The smaller, less-noticed sources of radioactive pollution need attention, too. Taken one by one, they may not amount to much. Taken together, and considered in a long-term perspective, they are a significant cause for concern.
We need to catalog them and understand any long-range hazard they may present. More importantly, we should avoid creating more of them. Engineers can find safer ways to power Earth satellites than by means of nuclear reactors and long-lived radio-isotopes. And those who operate nuclear fuel reprocessing plants can keep their noxious wastes out of the sea.
A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.