Trophic Position and Metabolic Rate Predict the Long-Term Decay Process of Radioactive Cesium in Fish: A Meta-Analysis

Abstract

Understanding the long-term behavior of radionuclides in organisms is important for estimating possible associated risks to human beings and ecosystems. As radioactive cesium (137Cs) can be accumulated in organisms and has a long physical half-life, it is very important to understand its long-term decay in organisms; however, the underlying mechanisms determining the decay process are little known. We performed a meta-analysis to collect published data on the long-term 137Cs decay process in fish species to estimate biological (metabolic rate) and ecological (trophic position, habitat, and diet type) influences on this process. From the linear mixed models, we found that 1) trophic position could predict the day of maximum 137Cs activity concentration in fish; and 2) the metabolic rate of the fish species and environmental water temperature could predict ecological half-lives and decay rates for fish species. These findings revealed that ecological and biological traits are important to predict the long-term decay process of 137Cs activity concentration in fish.

Agricultural Implications of the Fukushima Nuclear Accident (III)

“…Regression analyses showed that the estimated ecological half-life of radiocesium in Pacific cod was from 258 to 309 days; this value is consistent with values in other demersal fish caught off Fukushima Prefecture as reported by Wada et al (2013). Narimatsu et al (2015) further pointed out that the half-life was longer in old and larger individuals than in young and smaller individuals, probably a result of differences in metabolic rate and growth rates between age and body size classes as proposed in the study of Doi et al (2012). Radiocesium was rarely detected in the 2011 year-class, most likely because the fish were only exposed to very low levels of radiocesium when they started their life in the ocean bottom and after that radiocesium in the fish body was diluted by growth (Narimatsu et al 2015).…”

Fishing for Answers off Fukushima

“…Bioaccumulation is much higher in general in freshwater fish 7, as seen here. Uptake of cesium is balanced by loss back to the ocean, which increases with body size and metabolic rate (6). The loss rate is on average a few percent per day and has been shown to be faster if the cesium supply is pulsed, rather than a steady source (8).…”

Why Do the Radionuclide Concentrations of Pacific Cod Depend on the Body Size?

“…The estimated ecological half-life of radiocesium in Pacifi c cod was from 258 to 309 days; this value is consistent with values in other demersal fi shes caught off Fukushima Prefecture (Wada et al 2013 ). The half-life was longer in old and larger individuals than in young and small individuals, probably a result of differences in metabolic rate and growth rates between age and body size classes (Doi et al 2012 ). Radiocesium concentrations decreased to low levels soon after the accident in seawater and prey items (Buesseler et al 2011 ;Aoyama et al 2013 ) and have continued to decease in the period up to 2014 (Sohtome et al 2014 ).…”