Influence of non-equilibrium sorption on the vertical migration of 137Cs in forest mineral soils of Fukushima Prefecture

Sorption hypotheses and models are required for the prediction of 137Cs migration in soils contaminated after nuclear reactor accidents weapons tests. In assessment models, Kd (distribution coefficient) hypothesis sorption, which assumes that sorption is instantaneous, linear reversible, has often been coupled with convection-diffusion equation (CDE) to model migration. However, it fails describe velocities decrease time. Alternative equilibrium-kinetic (EK) sorption/desorption have suggested by laboratory experiments but not fully validated field conditions. This work addressed influence magnitude non-equilibrium conditions reinterpreting, an inverse approach, series profiles measured mineral forest plots located Fukushima Prefecture (2013–2018). Our results show inclusion significantly improves, compared equilibrium hypothesis, realism simulated profiles. Fitted parameters suggest a fast kinetic (half-time 1–7 h) pseudo-irreversible desorption rate 3.2 × 100–3.4 106 years), whereas (4.0 10−3 L kg−1 on average) only affects negligible portion inventory. By June 2011, such EK fitted our realistically reproduced same study site (Takahashi et al., 2015). Predictive modeling soil suggests strong persistence surface contamination 2030, exponential consistent those reported Chernobyl accident. demonstrates can be partially inferred from situ measurements. further controlled better estimate identify processes behind sorption.