Empirical evidence that mean soil contaminant concentration is not a conservative indicator of external exposure to wildlife

• Published in: Ecological Indicators
• Main Authors: Edda Bæk, Thomas G. Hinton, Lavrans Skuterud, James C. Beasley, Brit Salbu, Vikas C. Baranwal, Ole Christian Lind
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2023
• Subjects: Screening-level risk assessment; Model validation; External exposure; Free-ranging reindeer; GPS-coupled dosimeter; Cs-137 Chernobyl fallout; Ecology; QH540-549.5; Norway; Rangifer tarandus
• Online Access: https://doi.org/10.1016/j.ecolind.2023.110359; https://doaj.org/article/4118e1ed1685483d859639b9d9ec6633

Adequate information on external exposure is often a limiting factor in ecological risk assessments because of a lack of exposure data for free-ranging animals as they interact with a heterogeneous distribution of contaminants. Instead, most wildlife exposure data are estimated from model simulations. However, empirical exposure data are rarely available to verify model results, or to test fundamental assumptions inherent in exposure assessments. We used novel, GPS-coupled radiation dosimeters on reindeer (Rangifer tarandus) to quantify their external exposure for five months in a Chernobyl fallout affected mountainous area of Norway. The exposure data were then used to test a fundamental assumption in screening-level risk assessments: Mean soil contaminant concentrations can be used to conservatively estimate chronic external exposures to representative animals. External exposure and GPS coordinates were obtained hourly and compared to model simulations of exposure based on airborne surveys of 137Cs soil contamination. Our objectives were to determine 1) if modelled dose estimates based on mean 137Cs soil concentrations were conservative, and 2) if modelled dose estimates could be improved by adjusting for spatial–temporal heterogeneity of contaminants using 137Cs concentrations within reindeers’ GPS-defined home ranges and core areas. We found that external exposure modelled from mean soil contaminant concentrations underestimated exposure by 70% compared to empirical measurements from GPS-dosimeter collars worn on individual animals. Using area-weighted mean contaminant levels within the animals’ home range improved the model estimates, but still underestimated the field dosimeter data by 53%. The best estimate of external exposure was obtained when high-use areas within their home range, along with spatial heterogeneity of the contaminant, was accounted for by using area-weighted mean soil contaminant levels within GPS-derived core areas. Accounting for temporal use of core areas within animals’ home range ...