Effects of ionizing radiation on terrestrial plants and animals: A workshop report Page: 22 of 32
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effects, notably changes in plant and animal community composition caused by reduced
abundance of sensitive plant species, can also be observed.
Monitoring of contaminated ecosystems has additional advantages. Many such sites
involve exposures over a much larger spatial scale than is possible in a field experiment.
Sites where data relevant to radiological protection standards have been collected include
Mayak, Kyshtym, Chernobyl, Windscale, the DOE reservations, nuclear-weapons testing
sites throughout the world, uranium-mining sites, and regions with high natural
background radiation. Because of the larger spatial extent of exposures associated with
many of these sites, mobile animals can, at least in principle, be included. Moreover, the
range of ecosystem types in which monitoring studies have been performed is far greater
than the range for which experimental data are available. Whereas most experimental
studies have used primarily acute external exposures, monitoring studies involve both
internal and external exposures and, in many cases, chronic exposures.
Field studies are also subject to a variety of important limitations. Almost all
experimental studies, particularly those in which doses are high enough to produce
detectable biological effects, have been limited to acute external exposures. In the small
number of field experiments involving direct application of isotopes to plants or soils, dose
rates have been below biological effects thresholds; the results, therefore, are useful
primarily for estimating transfer coefficients. Experiments involving applied isotopes are
also subject to significant uncertainties owing to spatial variations in isotope application
and the difficulty of obtaining accurate dose measurements for internal exposures.
Background environmental variability is inevitably higher in field experiments than in
controlled laboratory settings, and sample sizes and numbers of replicates are usually
small. Thus, the minimum detectable biological effect is much larger in field experiments
than in laboratory experiments. Moreover, for practical reasons, experimental studies
have emphasized effects on sedentary species, especially plants, because observed dose-
response relationships are generally poor except for plants.
Monitoring studies are subject to additional uncertainties relating to the high spatial
heterogeneity of radionuclide deposition rates. For some of the most important
monitoring studies (e.g., Kyshtym), direct measurements of deposition rates are
unavailable; for others (e.g., Chernobyl), spatial patterns in deposition must be
interpolated from limited field sampling. Dose rates for monitoring studies conducted
outside the former Soviet Union have generally been too low to produce measurable
ecological effects. Because good principles of experimental design (e.g., replication,
controls) cannot be applied in monitoring studies, it is often impossible to unambiguously
distinguish between radiological effects and effects caused by chemical contamination,
habitat disturbance, or natural climatic variation. This is especially true for birds, mobile
mammals, and any situations in which doses were less than catastrophic. Moreover,
primary effects (i.e., direct effects of radionuclides on organisms) are difficult to
distinguish from secondary or indirect effects such as those resulting from plant
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Barnthouse, L.W. Effects of ionizing radiation on terrestrial plants and animals: A workshop report, article, December 1, 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc667255/m1/22/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.