Soil-plant Transfer Model Research Articles

Major controlling factors and prediction models for mercury transfer from soil to carrot

Soil-plant transfer models are needed to predict levels of mercury (Hg) in vegetables when evaluating food chain risks of Hg contamination in agricultural soils. A total of 21 soils covering a wide range of soil properties were spiked with HgCl2 to investigate the transfer characteristics of Hg from soil to carrot in a greenhouse experiment. The major controlling factors and prediction models were identified and developed using path analysis and stepwise multiple linear regression analysis. Carrot Hg concentration was positively correlated with soil total Hg concentration (R 2 = 0.54, P < 0.001), and the log-transformation greatly improved the correlation (R 2 = 0.76, P < 0.001). Acidic soil exhibited the highest bioconcentration factor (BCF) (ratio of Hg concentration in carrot to that in soil), while calcareous soil showed the lowest BCF among the 21 soil types. The significant direct effects of soil total Hg (Hgsoil), pH, and free Al oxide (AlOX) on the carrot Hg concentration (Hgcarrot) as revealed by path analysis were consistent with the result from stepwise multiple linear regression that yielded a three-term regression model: log [Hgcarrot] = 0.52log [Hgsoil] − 0.06pH − 0.64log [AlOX] − 1.05 (R 2 = 0.81, P < 0.001). Soil Hg concentration, pH, and AlOX content were the three most important variables associated with carrot Hg concentration. The extended Freundlich-type function could well describe Hg transfer from soil to carrot.

A dynamic model to calculate cadmium concentrations in bovine tissues from basic soil characteristics

A chain model was developed to calculate the flow of cadmium from soil, drinking water and feed towards bovine tissues. The data used for model development were tissue Cd concentrations of 57 bovines and Cd concentrations in soil, feed and drinking water, sampled at the farms were the bovines were reared. Validation of the model occurred with a second set of measured tissue Cd concentrations of 93 bovines of which age and farm location were known. The exposure part of the chain model consists of two parts: (1) a soil–plant transfer model, deriving cadmium concentrations in feed from basic soil characteristics (pH and organic matter content) and soil Cd concentrations, and (2) bovine intake calculations, based on typical feed and water consumption patterns for cattle and Cd concentrations in feed and drinking water. The output of the exposure model is an animal-specific average daily Cd intake, which is then taken forward to a kinetic uptake model in which time-dependent Cd concentrations in bovine tissues are calculated. The chain model was able to account for 65%, 42% and 32% of the variation in observed kidney, liver and meat Cd concentrations in the validation study.

Prediction of Cadmium uptake by brown rice and derivation of soil–plant transfer models to improve soil protection guidelines

Cadmium (Cd) levels in paddy fields across Taiwan have increased due to emission from industry. To ensure the production of rice that meets food quality standards, predictive models or suitable soil tests are needed to evaluate the quality of soils to be used for rice cropping. Levels of Cd in soil and rice grains were measured in 19 paddy fields across the western plains in Taiwan. Cadmium levels in soil range from less than 0.1 mg kg −1 to 30 mg kg −1. Measured Cd levels in brown rice were predicted very well ( R 2 > 0.8) based on Cd and Zinc in a 0.01 M CaCl 2 extract or a soil–plant transfer model using the reactive soil Cd content, pH, and cation exchange capacity. In contrast to current soil quality standards used in Taiwan, such models are effective in identifying soils where Cd in rice will exceed food quality standards.

An Exchange Method To Investigate the Kinetics of Cd Complexation in Soil Solutions

Knowledge of the dynamic speciation of metals in soil solution is necessary for soil-plant transfer models. The lability of a metal in a given context partly depends on the kinetics of interconversion between the free ion (M) and one complex (ML), governed by the association (c(k)a) and dissociation (c(k)d) rate constants of the reaction of formation of ML If only one single complex is assumed to be present in solution, a single kinetic experiment will enable estimation of ckd and cka', that is, the product of cka by the concentration of free ligand in solution. The method consists of the measurements over time of the radioactive metal remaining in solution after the labeling of a Ca resin--solution system in balanceforthe nonlabeled metal initially present. The method is described for Cd and was applied on four soil solution extracts. The order of magnitude of the estimated c(k)a'- and c(k)d-values was about 10(-3) s(-1). The advantages and drawbacks of the method are discussed.

Soil-to-plant transfer of radiocaesium for selected tropical plant species in Bangladesh

Soil-to-plant transfer factors (TF) of radiocaesium ( 137Cs) were determined under field condition for grassy vegetation grown in Bangladesh at contaminated land in the Atomic Energy Research Establishment (AERE) campus. TF values for rice, grass and grassy/root vegetations grown in the same type of soil were also measured under pot condition. TF values of 137Cs for grassy vegetation (2.4 × 10 −2–4.2 × 10 −2 with an average of 3.1 × 10 −2 ± 0.005) obtained under field condition were slightly lower than the values for grass and grassy/root vegetations (2.9 × 10 −2–6.6 × 10 −2 with an average of 4.8 × 10 −2 ± 0.01 for grass and grassy vegetations and 2.3 × 10 −2–5.6 × 10 −2 with an average of 4.0 × 10 −2 ± 0.009 for root vegetations, respectively) obtained under pot condition. However, TF values (9.0 × 10 −3–2.6 × 10 −2 with an average of 1.9 × 10 −2 ± 0.004) obtained for rice were about a factor of 4 lower than the values obtained for grass and grassy/root vegetations. When the properties of the AERE soils as input parameters were used in the soil–plant transfer model of Absalom, the estimated TF values (4.5 × 10 −2–6.7 × 10 −2 with an average of 5.3 × 10 −2 ± 0.006) were consistent with the measured values obtained for grass and grassy vegetations under pot condition, however, the model overestimates the TF values for rice.

The application of the RESTORE-EDSS to Chile

In Chile unexpectedly high 137 Cs activity concentrations in soils and in food products due to the weapons fallout in the 60* have been detected. This is partly due to the prevailing climatic conditions fliigh precipitation rates) and the soil characteristics of the Chilean soils especially in the 10* administrative Region Within an EC project of the 4 th framework: programme in Nuclear Fission Mastering Event of the Past (RESTORE 'restoration strategies for radioactive contaminated ecosystems') an EDSS (Environmental Decision Support System) has been developed which can be adapted to the ecological and site specific conditions of Chile by using information on soil properties, soil contamination and soil-plant transfer factors of n7 Cs for characteristic Chilean soil types and crops. These data can be used to identify areas which are potentially radioecological sensiUve i.e. will result in elevated radiation doses to people living and using these areas, and further more where countermeasure actions might he implemented. The EDSS will use the modern tools such as GIS (geographical information systems) and geostatisticat methods, recently developed dynamic soil-plant transfer models lo determine fluxes of radiocaesium, and dose calculation models. The system will provide an analysis of the present contamination with radiocaesium of Chile. Later it can be modified and applied for other radionuclides such as radiostrontiu m. Examples for the implementation of the EDSS and first results are presented.

Incorporating soil structure and root distribution into plant uptake models for radionuclides: toward a more physically based transfer model

Most biosphere and contamination assessment models are based on uniform soil conditions, since single coefficients are used to describe the transfer of contaminants to the plant. Indeed, physical and chemical characteristics and root distribution are highly variable in the soil profile. These parameters have to be considered in the formulation of a more realistic soil–plant transfer model for naturally structured soils. The impact of monolith soil structure (repacked and structured) on Zn and Mn uptake by wheat was studied in a controlled tracer application (dye and radioactive) experiment. We used Brilliant Blue and Sulforhodamine B to dye flow lines and 65Zn and 54Mn to trace soil distribution and plant uptake of surface-applied particle-reactive contaminants. Spatial variation of the soil water content during irrigation and plant growth informs indirectly about tracer and root location in the soil profile. In the structured monolith, a till pan at a depth of 30 cm limited vertical water flow and root penetration into deeper soil layers and restricted tracers to the upper third of the monolith. In the repacked monolith, roots were observed at all depths and fingering flow allowed for the fast appearance of all tracers in the outflow. These differences between the two monoliths are reflected by significantly higher 54Mn and 65Zn uptake in wheat grown on the structured monolith. The higher uptake of Mn can be modelled on the basis of radionuclide and root distribution as a function of depth and using a combination of preferential flow and rooting. The considerably higher uptake of Zn requires transfer factors which account for variable biochemical uptake as a function of location.