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

Data on the transfer of elements (such as heavy metals) and their radionuclides into organisms is needed for assessing environmental risks. The current data on many elements, species and environments is limited, but more information can be obtained both from field studies and experimental laboratory studies. However, it is essential to evaluate whether experimental studies adequately predict transfer in natural conditions. Moreover, because of the sparsity of species-specific empirical data, it is a common practice in current radioecological modelling to use data available for related species under the assumption that transfer into organisms is similar within broader taxonomic groups. Earthworms and ground beetles are examples of important invertebrates living near soil surface in terrestrial ecosystems. In this study, the transfer of 34 elements from soil to these organisms was studied in a field study conducted in boreal forest. The earthworm concentrations were compared to the values obtained in an experimental mesocosm study using soil from the field site and were found to be highly correlated. This indicates that the results of mesocosm studies can be used for predicting the transfer of elements from soil to fauna in natural conditions. Furthermore, concentrations in individual earthworm and beetle species were found to be similar to those observed in broader groups of related species, indicating that the generic approach used in current radioecological models may be useful for predicting uptake of elements into single species.

Uptake of Soil-Derived Carbon into Plants: Implications for Disposal of Nuclear Waste.

Radiocarbon (14C) is potentially significant in terms of release from deep geological disposal of radioactive waste and incorporation into the biosphere. In this study we investigated the transfer of soil-derived C into two plant species by using a novel approach, where the uptake of soil-derived C into newly cultivated plants was studied on 8000-year leftover peat in order to distinguish between soil-derived and atmospheric C. Two-pool isotope mixing model was used to reveal the fraction of soil C in plants. Our results indicated that although the majority of plant C was obtained from atmosphere by photosynthesis, a significant portion (up to 3-5%) of C in plant roots was derived from old soil. We found that uptake of soil C into roots was more pronounced in ectomycorrhizal Scots pine than in endomycorrhizal reed canary grass, but nonetheless, both species showed soil-derived C uptake in their roots. Although plenty of soil-derived C was available in canopy air for reassimilation by photosynthesis, no trace of soil-derived C was detected in aboveground parts, possibly due to the open canopy. The results suggest that the potential for contamination with 14C is higher for roots than for leaves.

Transfer of elements relevant to radioactive waste into chironomids and fish in boreal freshwater bodies.

Information on transfer of elements and their radionuclides is essential for radioecological modeling. In the present study, we investigated the transfer of Cl, Co, Mo, Ni, Se, Sr, U and Zn in a boreal freshwater food chain. These elements were selected on the basis that they have important radionuclides that might be released into the biosphere from various stages of the nuclear fuel cycle. Water, sediment, chironomid larvae (Chironomus sp.), roach (Rutilus rutilus) and perch (Perca fluviatilis) were sampled from two ponds near a former uranium mine and one reference pond located further away from the mining area. Concentrations measured in water, sediment and the three animal species indicated the importance of sediment as a source of uptake for most of the elements (but not Cl). This should be considered in radioecological models, which conventionally predict concentration in aquatic organisms from concentration in water. The results also show that the assumption of linear transfer (constant concentration ratio) may not be valid for elements into fish. The results of this study show that further basic research is needed to understand the fundamental processes involved in transfer of elements into freshwater organisms in order to develop radioecological models.

Content of soil-derived carbon in soil biota and fauna living near soil surface: Implications for radioactive waste.

14C is known as one of the radionuclides that have potential to be released into the biosphere from radioactive waste repositories and taken up by organisms. In this study, we used a novel approach to investigate the proportion of soil organic carbon (SOC) in invertebrates and microbial biomass. The study was conducted on a peatland site after the end of peat extraction. There was a large difference in the isotopic abundance of 14C between the 8000-year-old peat and air. We used a two-pool isotope mixing model to reveal the fraction of soil-derived C in the organisms and in dissolved organic carbon in soil water. The contribution of soil-derived C was found to be highest in microbial biomass (61%) and earthworms (22%). Some contribution of soil-derived C was detected in fungus gnats (2%), but not in other insects or in spiders. These findings are important for developing evidence-based radioecological models based on correct understanding of the relative contributions of atmospheric C vs. SOC in organisms.

Is developmental instability in chironomids a sensitive endpoint for testing uranium mine-affected sediments?

There is increasing interest in effects of radionuclides on non-human species, but methods for studying such effects are not well developed. The aims of the current study were to investigate the effects of uranium mine-affected sediments on non-biting midge Chironomus riparius and to compare sensitivity of different endpoints. The midge larvae were exposed in controlled laboratory conditions to sediments from two ponds downstream from an abandoned uranium mine and a reference pond not receiving water from the mining site. Quartz sand was used as an additional control. Developmental effects were assessed by evaluating emergence of adult midges, body mass, and fluctuating asymmetry (FA) in the length of wing upper vein. FA has been suggested to be a sensitive indicator of developmental instability, but the results of previous studies are inconsistent. In the present study, no difference in FA was observed between the treatment groups, but time to emergence was significantly delayed in the contaminated sediments. The approach used in this study (laboratory experiments with sediments from a contaminated site) avoids confounding due to uncontrolled environmental variables and adaptation to long-term contamination, which may mask effects on natural populations. Using this approach, we found no effects on FA of wing length. Time to emergence, in contrast, was found to be a more sensitive endpoint.