SREL Reprint #3764

The impact of sampling scale: A comparison of methods for estimating external contaminant exposure in free-ranging wildlife

Helen L. Bontrager1, Thomas G. Hinton2,3, Kei Okuda4, and James C. Beasley1

1Savannah River Ecology Laboratory, Warnell School of Forestry and Natural Resources,
University of Georgia, Aiken, SC 29808, USA
2Centre of Excellence in Environmental Radioactivity (CERAD), Faculty of Environmental Sciences
and Natural Resource Management, Norwegian University of Life Sciences,
P.O. Box 5003, N-1433 Ås, Norway
3Institute of Environmental Radioactivity, 1 Kanayagawa, Fukushima City, Fukushima 960-1296, Japan
4Faculty of Human Environmental Sciences, Hiroshima Shudo University, Hiroshima 731-3195, Japan

Abstract: The impacts of contaminants on wildlife are dose dependent, and thus being able to track or predict exposure following contamination events is important for monitoring ecosystem health. However, the ability to track exposure in free-ranging wildlife is often severely limited. Consequently, researchers have predominantly relied on simple methods for estimating contaminant exposures in wildlife with little regard for spatial contaminant heterogeneity or an animal's use of diverse habitats. We evaluated the influence sampling scale (i.e., how finely contaminant distribution and organism's spatial use of the landscape is mapped) has on (1) realism and (2) conservativeness of exposure estimates. To do this, we monitored the actual exposure of wild boar (Sus scrofa) in Fukushima, Japan to radioactive contamination using GPS-coupled contaminant monitors placed on individual animals. We compared empirical exposures to estimates generated by combining varying amounts of information about an individual boar's location and/or movement, with the distribution of contamination on the landscape. We found that the most realistic exposure estimates were produced when finer-scale contaminant distribution surveys (e.g., airborne surveys) were combined with more accurate estimates of an individual's space use (e.g., home ranges or core areas). Importantly, estimates of exposure based on single point surveys at a trap site (a simple method commonly used in the literature), did not correlate with actual exposure rates, suggesting dose-effects studies using this method may result in spurious conclusions. These results suggest that researchers seeking realistic estimates of exposure, such as in dose-effect studies, should ensure they have adequately accounted for fine-scale contaminant distribution patterns and areas of higher use by study organisms. However, conservative estimates of exposure (i.e., intentionally over-predicting exposure as is done in initial tiers of ecological risk analyses) were not as scale sensitive and could be achieved with a single known location and coarse contaminant distribution maps.

Keywords: Dose-effect; Fukushima; Radiation; Risk assessment; Sus scrofa; Wild boar

SREL Reprint #3764

Bontrager, H. L., T. G. Hinton, K. Okuda, and J. C. Beasley. 2024. The impact of sampling scale: A comparison of methods for estimating external contaminant exposure in free-ranging wildlife. Science of the Total Environment 921(171012).

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).