Päivi Roivainen

Soil-to-plant transfer of elements is not linear: Results for five elements relevant to radioactive waste in five boreal forest species

Element-specific concentration ratios (CRs) assuming that plant uptake of elements is linear are commonly used in radioecological modelling to describe the soil-to-plant transfer of elements. The goal of this study was to investigate the validity of the linearity assumption in boreal forest plants, for which only limited relevant data are available. The soil-to-plant transfer of three essential (Mo, Ni, Zn) and two non-essential (Pb, U) elements relevant to the safety of radioactive waste disposal was studied. Three understory species (blueberry, narrow buckler fern and May lily) and two tree species (Norway spruce and rowan) were included. Examining CRs as a function of soil concentration showed that CR was not constant but decreased with increasing soil concentrations for all elements and plant species. A non-linear equation fitted fairly well with the empirical data; the R(2)-values for this equation were constantly higher than those for the linear fit. The difference between the two fits was most evident at low soil concentrations where the use of constant CRs underestimated transfer from soil to plants. Site-specific factors affected the transfer of Mo and Ni. The results suggested that systematic variation with soil concentrations explains a part of the large variation of empirically determined CRs, and the accuracy of modelling the soil-to-plant transfer might be improved by using non-linear methods. Non-linearity of soil-to-plant transfer has been previously reported for a few different species, elements and environments. The present study systematically tested the linearity assumption for five elements (both essential and non-essential) and in five boreal forest species representing different growth traits and phylogenies. The data supported non-linearity in all cases.

Transfer of elements relevant to radioactive waste from soil to five boreal plant species.

In long-term safety assessment models for radioactive waste disposal, uptake of radionuclides by plants is an important process with possible adverse effects in ecosystems. Cobalt-60, (59,63)Ni, (93)Mo, and (210)Pb are examples of long-living radionuclides present in nuclear waste. The soil-to-plant transfer of stable cobalt, nickel, molybdenum and lead and their distribution across plant parts were investigated in blueberry (Vaccinium myrtillus), May lily (Maianthemum bifolium), narrow buckler fern (Dryopteris carthusiana), rowan (Sorbus aucuparia) and Norway spruce (Picea abies) at two boreal forest sites in Eastern Finland. The concentrations of all of the studied elements were higher in roots than in above-ground plant parts showing that different concentration ratios (CR values) are needed for modelling the transfer to roots and stems/leaves. Some significant differences in CR values were found in comparisons of different plant species and of the same species grown at different sites. However, large within-species variation suggests that it is not justified to use different CR values for modelling soil-to-plant transfer of these elements in the different boreal forest plant species.

Element interactions and soil properties affecting the soil-to-plant transfer of six elements relevant to radioactive waste in boreal forest

Cobalt (Co), lead (Pb), molybdenum (Mo), nickel (Ni), uranium (U), and zinc (Zn) are among the elements that have radioactive isotopes in radioactive waste. Soil-to-plant transfer is a key process for possible adverse effects if these radionuclides are accidentally released into the environment. The present study aimed at investigating factors affecting such transfer in boreal forest. The plant species studied were blueberry (Vaccinium myrtillus), May lily (Maianthemum bifolium), narrow buckler fern (Dryopteris carthusiana), rowan (Sorbus aucuparia) and Norway spruce (Picea abies). Regression analyses were carried out to investigate the effects of the chemical composition and physical properties of soil on the soil-to-leaf/needle concentration ratios of Co, Mo, Ni, Pb, U and Zn. Soil potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P) and sulphur (S) concentrations were the most important factors affecting the soil-to-plant transfer of the elements studied. Soil clay and organic matter contents were found to significantly affect plant uptake of Mo, Pb and U. Knowledge of the effects of these factors is helpful for interpretation of the predictions of radioecological models describing soil-to-plant transfer and for improving such models.

Occupational exposure to intermediate frequency and extremely low frequency magnetic fields among personnel working near electronic article surveillance systems

Cashiers are potentially exposed to intermediate frequency (IF) magnetic fields at their workplaces because of the electronic article surveillance (EAS) systems used in stores to protect merchandise against theft. This study aimed at investigating occupational exposure of cashiers to IF magnetic fields in Finnish stores. Exposure to extremely low frequency (ELF) magnetic fields was also evaluated because cashiers work near various devices operating with 50 Hz electric power. The peak magnetic flux density was measured for IF magnetic fields, and was found to vary from 0.2 to 4 µT at the cashiers seat. ELF magnetic fields from 0.03 to 4.5 µT were found at the cashiers seat. These values are much lower than exposure limits. However, according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) occupational reference levels for IF magnetic fields (141 µT for the peak field) were exceeded in some cases (maximum 189 µT) for short periods of time when cashiers walked through the EAS gates. As the ICNIRP reference levels do not define any minimum time for exposure, additional investigations are recommended to determine compliance with basic restrictions. Even if the basic restrictions are not exceeded, persons working near EAS devices represent an exceptional group of workers with respect to exposure to electromagnetic fields. This group could serve as a basis for epidemiological studies addressing possible health effects of IF magnetic fields. Compliance with the reference levels for IF fields was evaluated using both broadband measurement of peak fields and the ICNIRP summation rule for multiple frequencies. The latter was generally more conservative, and the difference between the two methods was large (>10-fold) for EAS systems using a 58 kHz signal with complex waveform. This indicates that the ICNIRP multiple frequency rule can be unnecessarily conservative when measuring complex waveforms.

Indoor transformer stations and ELF magnetic field exposure: use of transformer structural characteristics to improve exposure assessment

Previous studies have shown that populations of multiapartment buildings with indoor transformer stations may serve as a basis for improved epidemiological studies on the relationship between childhood leukaemia and extremely-low-frequency (ELF) magnetic fields (MFs). This study investigated whether classification based on structural characteristics of the transformer stations would improve ELF MF exposure assessment. The data included MF measurements in apartments directly above transformer stations (“exposed” apartments) in 30 buildings in Finland, and reference apartments in the same buildings. Transformer structural characteristics (type and location of low-voltage conductors) were used to classify exposed apartments into high-exposure (HE) and intermediate-exposure (IE) categories. An exposure gradient was observed: both the time-average MF and time above a threshold (0.4 μT) were highest in the HE apartments and lowest in the reference apartments, showing a statistically significant trend. The differences between HE and IE apartments, however, were not statistically significant. A simulation exercise showed that the three-category classification did not perform better than a two-category classification (exposed and reference apartments) in detecting the existence of an increased risk. However, data on the structural characteristics of transformers is potentially useful for evaluating exposure–response relationship.

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

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 234U, 59Ni and 210Pb 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.

A pilot study on the reproductive risks of maternal exposure to magnetic fields from electronic article surveillance systems

Abstract Purpose: We investigated the feasibility of a large-scale epidemiological study on reproductive effects of intermediate frequency (IF) magnetic field (MF) exposure among cashiers working near electronic article surveillance (EAS) systems. Materials and methods: The study cohort included 4157 women who had worked as cashiers in supermarkets with EAS devices (considered as exposed) or grocery stores without EAS devices (considered as unexposed) between 2008 and 2015. 536 births and 38 miscarriages occurred among these women during the study period, based on information from nationwide health registries. Measurements were also performed to characterize the MF exposure of cashiers. Results: Cashiers were found to be exposed to 8.2 MHz MFs only when passing by the gates at short distance. Static fields of about 0.1 mT were observed at cashier’s seat. Extremely low frequency MFs were higher at stores without EAS devices. No differences on the risk of miscarriage, reduced birth weight or preterm birth were observed between cashiers in different store types. Conclusions: Any further studies should attempt to include study subjects working near EAS systems that produce stronger IF MFs at kHz frequencies. Exposure to ELF MFs should be assessed as a possible confounding factor.

Assessment of Health Risks of Intermediate Frequency Magnetic Fields

Health effects of electromagnetic fields have been studied mainly focusing on extremely low frequency magnetic fields and radio frequency fields. Less attention has been paid to intermediate frequency magnetic fields (IF MFs) even though number of applications is increasing and information on potential health effects is sparse. We are conducting a series of studies to assess the exposure to IF MFs and the consequences of exposure.

Reply to Comment on “Maternal exposure to extremely low frequency magnetic fields: Association with time to pregnancy and foetal growth”

We thank de Vocht and Burstyn (2016) for their comments on our recent paper that investigated the possible association of maternal exposure to extremely low frequency magnetic fields (ELF MFs) with time-to-pregnancy and foetal growth (Eskelinen et al., 2016). De Vocht and Burstyn compare our study to their own study (de Vocht et al., 2014; de Vocht and Lee, 2014), and nicely point our important issues related to exposure assessment, measurement error, confounding and sample size. We greatly appreciate this valuable discussion, and wish to comment only a couple of issues at the end of de Vochts and Burstyns comments. De Vocht and Burstyn state that our conclusion “The results of the present study do not support the conclusion that ELF MF exposure would be associated with reduction in birth weight” is too strong. Of course, we did not want to say that our results disprove the previous findings by de Vocht and colleagues. We are fully aware of the limitations of our study, and have discussed those in our paper (Eskelinen et al., 2016). From a more general point of view it is difficult, if not impossible, for a scientific study to show that something (e.g., association between an environmental agent and disease) does not exist. Using the example by Karl Popper, a hypothesis of the form “black swans exist” would not be falsifiable. As we cannot disprove the hypothesis of an association between ELF MF and reduced birth weight, the only possible conclusions are that our study either supports or does not support the hypothesis. With no statistically significant associations found, the only remaining conclusion was that the hypothesis is not supported by the data. Disproving or accepting the null hypothesis that there is no association between ELF MFs and birth outcomes obviously requires more studies in addition to those by us and de Vocht et al. As pointed out by de Vocht and Burstyn (2016), it will be difficult to combine high statistical power (large study) and high quality exposure assessment. A possibleway forward is to conduct ameta-analysis, but thatwillmost likely also require more original studies, which all have their own strengths and weaknesses. As we state in the conclusions of our paper, we hope these further studies could reliably characterize the ELF MF exposure for high number of people and also to increase the number of highly exposed persons. A minor detail that needs to be commented is the comparison of effect sizes presented in the comments by de Vocht and Burstyn. They refer to our findings of a mean difference in grams of −45 with a 95% confidence interval of −547 g to 456 g for all spot measurements and