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The impact of the release of radionuclides from nuclear facilities
on non-human biota was assessed. Nuclear facilities examined included
all aspects of the uranium fuel chain, from mining and milling through
to power generation and waste management. Although nuclear facilities
release non-radioactive substances (e.g., metals, organic chemicals),
the effects of such non-radioactive substances were not considered in
this assessment.
Because of the variety of industrial activities and processes that
result in the release of a large number of radionuclides with different
radiological half-lives and chemical, biological and environmental properties,
sectorial assessments were conducted. The sectors and numbers of facilities
considered were as follows: five operating uranium mines and mills,
two uranium refineries and conversion plants, three stand-alone waste
management facilities and five nuclear power plants. Heavy water production
facilities were not included, because there is no production, use or
release of radionuclides from these facilities.
Uranium (U) and thorium (Th) and their decay chain daughter radionuclides
are the radionuclides of primary interest released from uranium mines
and mills, whereas uranium is the main radionuclide released from uranium
refining and conversion facilities. Radionuclides of interest in tailings
management facilities at uranium mines and mills are primarily 226Ra
and uranium, although other radionuclides (e.g., 3H, 14C, 60Co, 90Sr
and 137Cs) may also be important in some waste management facilities.
Fission and activation products released from nuclear generating stations
include 3H, 14C, 51Cr, 54Mn, 59Fe, 60Co, 65Zn, 90Sr, 95Zr, 106Ru, 124Sb,
128–135I, 137Cs and 144Ce. Releases of radionuclides from these
facilities are primarily to air or to water. Emissions to air will result
in the deposition of particle-reactive radionuclides and increased scavenging
of radionuclides from the plume with distance from the source. Mobile
radionuclides such as the inert gases will disperse quickly and reach
background concentrations a short distance (a few kilometres) from the
source. Most of the radionuclides released are particle reactive and
partition either from water to sediment or from air to soil.
There are two modes of toxic action for the radionuclides assessed:
chemical and radiological. Because of its relatively low specific activity,
uranium is the only radionuclide examined that has greater potential
to cause chemical rather than radiological toxicity. Radiotoxicity can
result from exposure to ionizing radiation emitted by radionuclides.
Radiotoxicity differs from chemical toxicity in that radiation dose,
the measure of radiation exposure, results from radionuclides incorporated
in tissues (internal dose) and from external radionuclides (external
dose) that emit radiation adjacent to the organism.
For the chemical toxicity of uranium, releases are largely restricted
to the front end of the nuclear fuel chain: namely the mining, milling
and refining of uranium and the management of mill tailings. Comparison
of exposure values with Estimated No-Effects Values (ENEVs) indicates
the potential for localized harm to organisms resulting from current
releases of uranium and uranium compounds contained in effluents from
three older operating uranium mines and mills. However, there was no
evidence of environmental harm from exposure to uranium at two new uranium
mines and mills with state-of-the-art effluent facilities.
There is relatively little evidence that exposure to ionizing radiation
resulting from current releases of radionuclides from nuclear facilities
is causing environmental harm. Comparison of exposure values with ENEVs
does suggest that there is potential for biota to be harmed from exposure
to radiation at two locations near operating mines and at one stand-alone
waste management facility as a consequence of current releases. However,
uncertainties and some conservative assumptions associated with risk
estimates for ionizing radiation, complicate their interpretation.
Based on available data concerning the effects from exposure
to uranium, it has been concluded that (i) releases of uranium and uranium
compounds contained in effluent from uranium mines and mills are entering
the environment in quantities or concentrations or under conditions
that have or may have an immediate or long-term harmful effect on the
environment or its biological diversity; and (ii) releases of uranium
and uranium compounds from uranium refineries and conversion facilities,
stand-alone waste management facilities, power reactors and their associated
waste management facilities, and research reactors are not entering
the environment in quantities or concentrations or under conditions
that have or may have an immediate or long-term harmful effect on the
environment or its biological diversity. Based on available data concerning
the effects from exposure to ionizing radiation, it has been concluded
that ionizing radiation emitted by radionuclides released from uranium
mines and mills, uranium refineries and conversion facilities, stand-alone
waste management facilities, power reactors and their associated waste
management facilities, and research reactors is not entering the environment
in quantities or concentrations or under conditions that have or may
have an immediate or long-term harmful effect on the environment or
its biological diversity. Therefore, it is concluded that releases of
uranium and uranium compounds contained in effluent from uranium mines
and mills are “toxic” as defined in Section 64 of the Canadian
Environmental Protection Act, 1999 (CEPA 1999).
Since it is concluded that uranium and uranium compounds contained
in effluent from uranium mines and mills are “toxic” as
defined in Section 64 of CEPA 1999, it is recommended that investigations
of options to reduce exposure to uranium from these sources be considered
a high priority. Discussions have been initiated with the Canadian Nuclear
Safety Commission (CNSC) to determine whether it will be possible to
manage these releases under the Nuclear Safety and Control Act. It is
proposed that the process for risk management be formalized in an annex
to the memorandum of understanding that has been negotiated between
Environment Canada and the CNSC.
Risk quotients calculated for ionizing radiation indicate limited potential
for harmful effects on the environment. The indicators of risk were
fairly low, however, especially considering the uncertainties and somewhat
conservative assumptions made when estimating risks for some biota.
It is nevertheless believed that an increase in environmental concentrations
of radionuclides could significantly increase risks, particularly at
uranium mines and mills and stand-alone waste management facilities.
It is thus recommended that releases of radionuclides from such facilities
be regularly monitored through existing mechanisms to evaluate whether
risk management initiatives may be needed for ionizing radiation in
the future. It is important that operators of such facilities recognize
that if information in their possession, such as monitoring data, shows
a significant increase in near-field radionuclide concentrations or
loadings, such information may be subject to reporting under Section
70 of CEPA 1999.
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