The scientific literature is a good source of information about soil-to-plant transfer, usually documented as mean concentration ratios. It does not provide, however, good information about variation in concentration ratio values, because most studies are done with limited numbers of crops and soils. Fortunately, a suitably large and diverse database is available from the International Union of Radioecologists that can be used to investigate variation. It has a total of over 7,000 concentration ratio values for over 22 elements. This paper reports on analysis of the geometric standard deviations obtained from the database. We assert that geometric standard deviation values are comparable and transferable among elements, so that geometric standard deviations calculated from large databases can be applied to other elements when there is a paucity of data. For a fully generic situation, where neither crops nor soil types are known, the geometric standard deviations is typically about 6. This implies a 1,300-fold range to encompass 95% of the data. For concentration ratios obtained for crops of interest on a specific site, the geometric standard deviation values are much lower, about 1.5. This still implies a fivefold range to encompass 95% of the data. Other values of geometric standard deviations for intermediate levels of information are provided. These estimates of geometric standard deviation are important to and appropriate for stochastic simulations of the impacts of soil contamination on crops and subsequent food chains. They are also important to the inclusivity of concentration ratios value distributions for unusual but perhaps important crops and settings.

Transfer of soil contaminants into the food chain has long been a concern. However, certain aspects of the pathways involved have not been fully investigated. One is the enrichment of contaminant concentrations through physical processes such as size-sorting of soil particles. Fine particles selected from soil by processes such as adhesion onto plants will have much higher contaminant concentrations than the original soil. A saturation kinetics model of the process of soil adhesion to leaf surfaces was developed. The model helps identify the parameters that are least-well known and need experimental support. The ratio of clay and sand wash-off half times was especially important. With nominal values for the input parameters, estimated enrichments agreed well with observations to date, and ranged from slightly over unity for medium- and fine-textured soils to about tenfold for sandy soils. With a few reasonable assumptions, the model was generalised to apply to other soil adhesion scenarios such as adhesion to skin. The generalised model can be applied with minimal need for setting-specific information.

Plants growing on soil contaminated with 14C can receive the radionuclide from both direct uptake through the roots or indirect uptake from the atmosphere. The contribution from the atmosphere depends on the rate of volatilization from the soil, the size of the source area, and the meteorological dispersion conditions. An atmospheric dispersion relationship was used to calculate the air concentration for a given area source term. The air concentration was then used to estimate the flux to foliage, which was compared with direct plant uptake through the roots. The ratio of atmospheric to root uptake pathways depended on plant height and source area, exceeding unity when the fetch was greater than a few meters for bean plants, but much greater for maize. A very large fetch, greater than 1000 m, is required before a uniform specific activity throughout the local biosphere can be assumed for a soil source. This quantitative analysis describes the limitations for calculations and experiments used to define simplified transfer coefficients for 14C from soil to vegetation.

Ionizing radiation at very low doses frequently has a stimulating or hormetic effect on the growth of organisms. Irradiation of seed before planting can stimulate early plant growth, leading to advanced maturity and increased yield. The unreliability of this response has limited its application. However, the technique has been extensively studied and now is practiced on a large scale on some farms in certain countries. Our research has addressed various factors that may determine the stimulation response with the goal of developing an ability to predict the occurrence of increased economic yield. In this paper, we discuss several of these factors in light of our data and data from other field studies in Canada. A hormesis response was observed for most species studied, but varied among cultivars and among seed lots within a cultivar. Seed condition may be the underlying factor in these effects. The response was most frequently evident at very early stages of growth and was often masked in subsequent growth. This suggests that the hormesis phenomenon in seeds may be quite common and is not reliably manifest in advanced maturity or yield increases because of environmental effects. Storage time after irradiation must be minimized to gain the greatest response. There is little evidence to suggest that the photon energy or dose rate of the radiation source is an important factor.