Nonlinear transfer of elements from soil to plants: impact on radioecological modeling

Abstract

In radioecology, transfer of radionuclides from soil to plants is typically described by a concentration ratio (CR), which assumes linearity of transfer with soil concentration. Nonlinear uptake is evidenced in many studies, but it is unclear how it should be taken into account in radioecological modeling. In this study, a conventional CR-based linear model, a nonlinear model derived from observed uptake into plants, and a new simple model based on the observation that nonlinear uptake leads to a practically constant concentration in plant tissues are compared. The three models were used to predict transfer of (234)U, (59)Ni and (210)Pb into spruce needles. The predictions of the nonlinear and the new model were essentially similar. In contrast, plant radionuclide concentration was underestimated by the linear model when the total element concentration in soil was relatively low, but within the range commonly observed in nature. It is concluded that the linear modeling could easily be replaced by a new approach that more realistically reflects the true processes involved in the uptake of elements into plants. The new modeling approach does not increase the complexity of modeling in comparison with CR-based linear models, and data needed for model parameters (element concentrations) are widely available.

Substratum influences uptake of radium-226 by plants

“…Before definite conclusions can be drawn for potential applications such as the characterization of present and past pollution and phytoremediation, the differences observed in the radium uptake need further confirmation and the processes need to be clarified. In particular, the RSP distributions suggesting that soil-to-plant transfer of 226 Ra and other radionuclides could be lognormal, so far not considered in most radioecological models (e.g., Whicker et al, 1999;Tuovinen et al, 2016), would need to be studied in details at control sites. A systematic comparison of our effective 226 Ra concentration approach (giving effective concentrations) with other well-established methods such as gamma and alpha spectrometry, liquid scintillation counting, and mass spectrometry (giving total concentrations) should be considered in the future.…”

Analysis of 238U, 226Ra, and 210Pb transfer factors from soil to the leaves of broadleaf tree species

“…This in dicated that more than 65 % of U, Ra, and Pb TF vari ations might be ex plained only by the de creas ing trend of cor re spond ing ac tiv ity con cen tra tion in the soil, re gardless of bi o log i cal dif fer ences be tween broadleaf species. That the soil con cen tra tion is one of the main factors caus ing TF vari a tion (and de crease) is also shown for ura nium and lead TF for the parts of the tree (leaf, nee dle, root), at two bo real for est sites [11]. Sim i larly, Noskova et al [27] re ported that for the above ground plant parts of Sorbus aucuparia and Betula pubescens trees 238 U up take de vi ated less from the men tioned decreas ing trend com pared to 226 Ra be cause ra dium uptake by plants might be more sen si tive to changes in the physicochemical char ac ter is tics of soil.…”

“…3 im plied that ac tiv ity con cen tra tions in tree leaves (C leaves ) are a non-lin ear func tion of ac tiv ity con cen trations in the soil (C soil ) of the type: C leaves = a C soil b with pa ram e ter val ues a > 0 and 1 < b < 1. This is a reg u larly ob served power func tion that re flects the non-lin ear ity in the soil to plant trans fer of the es sen tial and non-es sen tial el e ments [11,13,25,27]. To ex trap o late these ob tained re sults, it was ex am ined whether the con cen tra tion in leaves would be zero when the con cen tra tion in the soil is zero.…”

“…By def i ni tion, trans fer from soil to plant is consid ered as an equi lib rium pro cess when the nat u rally oc cur ring radionuclide ac tiv ity con cen tra tion in the plant is lin early re lated to its con cen tra tion in the soil, im ply ing a con stant TF in de pend ent of soil con cen tration [10][11][12][13]. But, be cause plant up take is a com plex pro cess af fected by char ac ter is tics such as the radionuclides' physicochemical form, soil type, the phys i cal and chem i cal prop er ties of the soil, the type and the bi o log i cal prop er ties of plants and cli mate con di tions, a de vi a tion from lin ear ity and a large variabil ity of mea sured TF val ues is pro duced [12][13][14][15].…”

Transfer of elements from soil to earthworms and ground beetles in boreal forest

“…The use of CR values in radioecological models is based on the assumption that uptake of elements into organisms is linear and can therefore be described by a constant CR. Although this assumption may not be valid (Tuovinen et al 2011 , 2016a , b ), CR-based modelling is widely used in radioecology. It is therefore of interest to compare the CR values found in this study to those published elsewhere.…”