Sir

Some points in your welcome coverage of the radioactive waste water leak from the Chalk River Laboratories of Atomic Energy of Canada Limited (AECL) into the Ottawa River need clarification (Nature 387, 747; 1997).

For example, the statement that the “Canadian government has ordered a halt to the disposal of liquid waste from Atomic Energy of Canada's main nuclear research site” is only partly correct. Yes, discharge of liquid waste to the liquid dispersal area was suspended. But large quantities of liquid wastes are still routinely discharged directly into the Ottawa River through three separate sewer systems. One of them, the process sewer, has an outfall 114 metres from the shore at a depth of 17 metres. It carries waste from the NRU reactor and the heavy-water upgrading facility. Wastes released from this outfall in 1995 included 20,000 GBq of tritium, 4,200 GBq of sodium-24, 72 GBq of caesium-137 and 0.4 GBq of various plutonium isotopes.

The fact that the total amount of tritium released in the recently reported leaks (570 GBq per month) corresponded to only 0.01 per cent of the legally permissible limits on releases from the site does not allay concerns of downstream residents, nor do we think it should. What it does do is to call into question radionuclide release limits for the Chalk River site.

These limits, calculated in 1982 by a staff member at the Chalk River facility, are several hundred times higher than those for the four CANDU reactors at the Pickering A generating station. Not only are the permissible releases very high (for example, 3.5 × 108 GBq of tritium per year), but they are applied to each individual isotope and point of release. In all, some 60-odd radionuclides may be released into the Ottawa River in amounts totalling more than 40 billion billion Bq each year.

The point that “government action seems to have been prompted by public concern rather than evidence of a clear danger” is interesting. Some would argue that discharging large quantities of carcinogenic, mutagenic radionuclides into a drinking-water source used by millions of Canadians is inevitably dangerous.

It is true, however, that studies quantifying the damage in populations downstream have not yet been done. Limited environmental data are available that show contamination of local beaches, fish and drinking-water supplies for communities as far downstream as Ottawa. Perhaps you will carry a subsequent chapter in this story some time in the future.