Environmental radiological protection
There are fundamental differences in determining the risk to humans following exposure to
radiation and the risks to a radioactively contaminated environment. Human risk analyses largely
focuses on cancer risks to individuals. Dose-response relationships are sufficiently established
that risk factors (i.e. probability of lethality from cancer per unit of dose) are established. In
contrast, ecological risk to non-human biota is seldom concerned with individuals, but instead, to
populations of plants and animals. Management of the environment centers on a viable population
of organisms, not on single individuals within the population. Endpoints for ecological risks are
not cancer oriented, but instead include a wide assortment of effects ranging from chromosomal
damage to reduced reproductive success. The dose-response relationships for these endpoints are
not established, and therefore there are no risk factors that equate dose to the probability of an
outcome.
The criteria for determining if an ecosystem is at risk from radioactive contamination are
currently changing. Traditionally, the paradigm for protecting the environment was that if humans
are protected then so is the rest of the environment (IAEA, 1992). That is, the protection criterion
for humans (1 mSv / year) was considered to be sufficiently restrictive that populations of non-
humans living in the same environment would be sufficiently protected. The International
Commission on Radiological Protection (ICRP) recognised the need to provide more quantitative
advice on environmental protection, and that a clear framework was required to assess the
relationships between exposure and dose, dose and effects, and any consequences of effects. The
ICRP has stated that the framework they are developing for environmental protection should
complement the approach used for the protection of humans (ICRP, 2009). Consequently, the
ICRP has suggested a similar reference-model approach as used for humans (
i.e.
“Reference
Man”) for non-human biota. They have, therefore, proposed a small set of “Reference Animals
and Plants” (RAPs) for which reference dosimetric models have been developed and knowledge
on radionuclide uptake and radiation effects collated.
The endpoints considered to be most relevant in determining risks to non-human biota are
increased mortality, increased morbidity and decrease reproductive output. Of the three, changes
in reproduction are thought to be the most sensitive to radiological exposures. Much more data
are needed, however, before we can confidently predict population level impacts to non-human
biota as a function of radiological exposures. Data are particularly scarce for chronic, low-level
exposures; exposures over several generations; and when radiological exposures are combined
with other types of contaminants or stressors.
The ability to predict population level effects under such scenarios are complicated by the large
natural variation in sensitivities to radiation among the individuals within a population.
Additionally, indirect effects occur, compensating mechanisms exist, and adaptation to the
radiological exposures can take place. An example of an indirect effect is the greater abundance
of resources (i.e. food, water, light, etc.) available to radioresistant individuals when
radiosensitive individuals decline within a population. The same analogy holds relative to a
greater abundance of resources available to radioresistant populations within a community when
radiosensitive populations decline (i.e. one species of insect declines leaving more resources to a
radioresistant insect species occurring within the same community). Such interactions are
Radiation protection of the environment: providing knowledge and skills to the user
community
Tom Hinton
French Institute for Radiation Protection and Nuclear Safety Page 6 of 7
18-Mar-14
https://wiki.ceh.ac.uk/x/hI9BBw
extremely difficult to predict. Likewise, compensating mechanisms have been documented in
populations of exposed animals that complicate the prediction of effects. An example of a
compensating mechanism is provided by Blaylock et al. (1969). They documented an increased
mortality of fish embryos exposed to a dose rate of 4 mGy/d in a contaminated lake. This effect,
however, was compensated for when the fish produced larger brood sizes, with the net result that
no effect was observed to the population.
Several organizations and research groups are actively seeking to improve our knowledge of
radiation impacts on the environment, and to derive benchmarks of acceptable dose rates that will
be considered protective of the structure and function of ecosystems. Consolidation of data within
a common database is augmenting their efforts. A radiation effects database, called
FREDERICA, has been developed and is freely available on line at
www.frederica-online.org
(Copplestone et al. 2008). See the accompanying lecture notes and power points slides of David
Copplestone on the derivation of benchmarks for non-human biota, and Hinton and Whicker
(1997).
Considerable uncertainty and controversy remains relative to the effects from chronic, low-level
exposures to radiation. Much can be learned from the Chernobyl accident and the multiple
generations of biota that have been exposed within the contaminated 30-km zone since 1986. A
United Nations subcommittee reviewed the environmental effects from the Chernobyl accident
(Hinton et al., 2007), and their conclusions form a major component of my accompanying power
point presentation. Other scientists have since documented effects at Chernobyl from dose rates
previously considered safe to biota (see power point slides). Much healthy debate exists on this
topic. Major data gaps undoubtedly exist in the following areas:
What are the effects from chronic, low-level exposures to radiation?
What is the extent of inherited, transgenerational effects to populations?
What is the significance of molecular effects to individuals and populations of biota?
How are effects from radiation altered when organisms are exposed to other stressors?
These questions are not unique to radiation ecology, but are also taxing the scientific abilities
within ecotoxicology relative to other types of contaminants (Eggen et al. 2004).
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