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This work investigated the vertical distribution and fractionation of uranium and thorium in soils under contrasting arable and woodland sites based on the same parent material. The effect of long-term application of phosphate fertilizer on U and Th concentrations in the arable soil was also assessed. The arable surface soils contained higher amounts of U compared with underlying layers and the woodland soil profile; by contrast, the Th distributions were very similar in both arable and woodland soils. The U and phosphate concentration profiles within the arable soil were broadly similar; U was strongly associated with Ca (r = 0.94) and soil P content (r = 0.86) whereas the U concentration profile in the woodland soil was virtually uniform with depth. The 'excess' U in arable soil, associated with long term P fertilizer application, was approximately 2.5 kg ha- 1 with 80% in the top 30 cm of the soil profile. A sequential extraction technique was used to fractionate U and discriminate between 'reactive' (non-residual) and 'residual' forms of U. The reactive U was adsorbed, mainly by organic matter and Fe-Mn oxides in the arable topsoil and there was a very strong relationship between reactive U and soil phosphate content in the arable soil (r = 0.99, P < 0.001). The 'excess' U accumulated in the arable topsoil was also considerably more reactive than the co-existing native U. Thus the reactive fraction of the excess U ranged from 29 to 42% compared with 14 to 15% reactivity of the native U. Thorium in both soils showed a very consistent, and low, reactivity down the soil profile at about 4% of total soil Th content (96% residual), bound almost completely to humus. [ABSTRACT FROM AUTHOR]

Aim: The primary aim of this study was to determine the selenium (Se) and iodine (I) food concentrations and dietary intake of the population living in the Kurdish controlled region of northern Iraq. We also assessed the extent to which iodised salt contributes to dietary iodine intake., Methodology: Foods and samples of salt and drinking water were analysed, including 300 crops samples from 40 local farms. The results, supplemented by food composition data, were used to assess dietary Se and I intake for 410 volunteers using a semi-quantitative food questionnaire. To directly investigate the nutritional status of individuals, urine samples were also collected from participants., Results: Selenium intake was mainly supplied by protein and cereal sources. Calculated median dietary intake of Se was 62.7 µg d -1 (mean = 66.3 µg d -1 ) with c. 72 % of participants meeting or exceeding dietary reference intake recommendations for age. Median dietary intake of I, excluding salt consumption, was 94.6 µg d -1 (mean 100.2 µg d -1 ), increasing to 607.2 µg d -1 when salt (of which >90 % was iodized) was included. Salt intake was estimated to be c.13.5 g d -1 (5400 mg Na d -1 ) which greatly exceeds WHO recommended intake (< 2000 mg d -1 of Na). Urine iodine concentrations indicated that 98 % of school aged children had excessive iodine intake (≥300 µg L -1 ) and 80-90 % of all study participants had above average or excessive iodine intake (≥200 µg L -1 )., Conclusions: Poultry and rice are the main sources of dietary Se to this population but around a third of children receive an inadequate Se intake. Fresh fruit and vegetables are the main sources of dietary I, but consumption of local foods cannot supply adequate I without iodised salt supplementation. Consumption of iodized salt well above recommended amounts is supplying this population with substantial iodine intake. Interventions to reduce salt intake would help to limit excessive iodine intake whilst also reducing cardio-vascular risks from Na consumption., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier GmbH.. All rights reserved.)

Habitat loss, climate change, environmental contaminants, and parasites and pathogens are among the main factors thought to act singly or together in causing amphibian declines. We tested for combined effects of neonicotinoid pesticides and parasites (versus parasites-only) on mortality, growth, and white blood cell profiles of a model amphibian: the northern leopard frog (Rana pipiens). We first exposed infectious stages of frog trematodes (cercariae of Echinostoma spp.) to low and high concentrations of thiamethoxam or clothianidin versus water-only controls. There were no differences in survival of trematode cercariae between treatments. For the main experiment, we exposed tadpoles to clean water versus high concentrations of clothianidin or thiamethoxam for 2 weeks and added trematode cercariae to all tanks after 1 week. Exposure of tadpoles and parasites to high concentrations of thiamethoxam or clothianidin did not affect parasite infection success. Tadpole survival was not different between treatments before or after parasite addition and there were no significant differences in tadpole snout-to-vent lengths or developmental stages between treatments. Tadpoles exposed to thiamethoxam + parasites had smaller widths than parasite-only tadpoles, whereas tadpoles exposed to clothianidin + parasites had higher eosinophil to leukocyte ratios compared to parasite-only tadpoles. Tadpoles of both neonicotinoid + parasite treatments had significantly lower monocyte to leukocyte ratios relative to parasite-only tadpoles. High concentrations of neonicotinoid combined with parasites appear to influence tadpole immune function important for further defense against parasites and pathogens. This work highlights the need for more holistic approaches to ecotoxicity studies, using multiple stressors.

Uranium may pose a hazard to ecosystems and human health due to its chemotoxic and radiotoxic properties. The long half-life of many U isotopes and their ability to migrate raise concerns over disposal of radioactive wastes. This work examines the long-term U bioavailability in aerobic soils following direct deposition or transport to the surface and addresses two questions: (i) to what extent do soil properties control the kinetics of U speciation changes in soils and (ii) over what experimental timescales must U reaction kinetics be measured to reliably predict long-term of impact in the terrestrial environment? Soil microcosms spiked with soluble uranyl were incubated for 1.7 years. Changes in U VI fractionation were periodically monitored by soil extractions and isotopic dilution techniques, shedding light on the binding strength of uranyl onto the solid phase. Uranyl sorption was rapid and strongly buffered by soil Fe oxides, but U VI remained reversibly held and geochemically reactive. The pool of uranyl species able to replenish the soil solution through several equilibrium reactions is substantially larger than might be anticipated from typical chemical extractions and remarkably similar across different soils despite contrasting soil properties. Modelled kinetic parameters indicate that labile U VI declines very slowly, suggesting that the processes and transformations transferring uranyl to an intractable sink progress at a slow rate regardless of soil characteristics. This is of relevance in the context of radioecological assessments, given that soil solution is the key reservoir for plant uptake., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Grain and soil were sampled across a large part of Amhara, Ethiopia in a study motivated by prior evidence of selenium (Se) deficiency in the Region's population. The grain samples (teff, Eragrostis tef, and wheat, Triticum aestivum) were analysed for concentration of Se and the soils were analysed for various properties, including Se concentration measured in different extractants. Predictive models for concentration of Se in the respective grains were developed, and the predicted values, along with observed concentrations in the two grains were represented by a multivariate linear mixed model in which selected covariates, derived from remote sensor observations and a digital elevation model, were included as fixed effects. In all modelling steps the selection of predictors was done using false discovery rate control, to avoid over-fitting, and using an α-investment procedure to maximize the statistical power to detect significant relationships by ordering the tests in a sequence based on scientific understanding of the underlying processes likely to control Se concentration in grain. Cross-validation indicated that uncertainties in the empirical best linear unbiased predictions of the Se concentration in both grains were well-characterized by the prediction error variances obtained from the model. The predictions were displayed as maps, and their uncertainty was characterized by computing the probability that the true concentration of Se in grain would be such that a standard serving would not provide the recommended daily allowance of Se. The spatial variation of grain Se was substantial, concentrations in wheat and teff differed but showed the same broad spatial pattern. Such information could be used to target effective interventions to address Se deficiency, and the general procedure used for mapping could be applied to other micronutrients and crops in similar settings., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

To understand the dynamic mechanisms governing soil-to-plant transfer of selenium (Se), technetium-99 ( 99 Tc) and iodine (I), a pot experiment was undertaken using 30 contrasting soils after spiking with 77 Se, 99 Tc and 129 I, and incubating for 2.5 years. Two grass species (Agrostis capillaris and Lolium perenne) were grown under controlled conditions for 4 months with 3 cuts at approximately monthly intervals. Native (soil-derived) 78 Se and 127 I, as well as spiked 77 Se, 99 Tc and 129 I, were assayed in soil and plants by ICP-MS. The grasses exhibited similar behaviour with respect to uptake of all three elements. The greatest uptake observed was for 99 Tc, followed by 77 Se, with least uptake of 129 I, reflecting the transformations and interactions with soil of the three isotopes. Unlike soil-derived Se and I, the available pools of 77 Se, 99 Tc and 129 I were substantially depleted by plant uptake across the three cuts with lower concentrations observed in plant tissues in each subsequent cut. Comparison between total plant offtake and various soil species suggested that 77 SeO 4 2- , 99 TcO 4 - and 129 IO 3 - , in soluble and adsorbed fractions were the most likely plant-available species. A greater ratio of 127 I/ 129 I in the soil solid phase compared to the solution phase confirmed incomplete mixing of spiked 129 I with native 127 I in the soil, despite the extended incubation period, leading to poor buffering of the spiked available pools. Compared to traditional expressions of soil-plant transfer factor (TF total ), a transfer factor (TF available ) expressed using volumetric concentrations of speciated 'available' fractions of each element showed little variation with soil properties., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Element cycling in the terrestrial environment is heavily reliant upon processes that occur in soil solution. Here we present the first application of microdialysis to sample iodine from soil solution. In comparison to conventional soil solution extraction methods such as Rhizon™ samplers, centrifugation, and high-pressure squeezing, microdialysis can passively sample dissolved compounds from soil solution without altering the in-situ speciation of trace elements at realistic soil moisture conditions. In order to assess the suitability of microdialysis for sampling iodine, the permeability factors and effect of perfusion flowrate on I - and IO 3 - recovery was examined in stirred solutions. Furthermore, microdialysis was used to sample native soluble iodine at a range of water contents and iodine-enriched soils to investigate iodine soil dynamics. Total iodine concentrations were measured using ICP-MS. Inorganic species and the molecular weight distribution of organically bound iodine were determined by anion exchange and size exclusion chromatography (SEC) coupled to an ICP-MS, respectively. The most effective recovery rates in stirred solution were observed with the slowest perfusion flowrate yielding 66.2 ± 7.1 and 70.5 ± 7.1% for I - and IO 3 - , respectively. Microdialysis was proven to be capable of sampling dissolved iodine from the soil solution, which accounted for <2.5% of the total soil iodine and speciation followed the sequence: organic-I > I -  > IO 3 - . The use of SEC coupled to (i) UV and (ii) ICP-MS analysis provided detail regarding the molecular weight distribution of dissolved org-I compounds. Dissolved org-I was detected with approximate molecular weights between 0.1 and 4.5 kDa. The results in this study show that microdialysis is a suitable technique for sampling dissolved iodine species from soils maintained at realistic moisture contents. In addition, inorganic iodine added to soils was predominately bound with relatively low molecular weight (<4.5 kDa) soluble organic matter., (Crown Copyright © 2019. Published by Elsevier Ltd. All rights reserved.)

The current availability of Pb in Egyptian soils and associated plants were studied in 15 locations (n=159) that had been historically subjected to industrial and automobile Pb emissions. Isotopic dilution with enriched 204 Pb was used to estimate the soil Pb labile pool (Pb E ); results showed that %Pb E values were mostly <25% which is likely due to the alkaline nature of the soils. Nonetheless, lability of Pb was significantly higher in urban and industrial locations indicating greater reactivity of anthropogenic Pb in comparison to geogenic-Pb. A plot of 206 Pb/ 207 Pb vs 208 Pb/ 207 Pb showed that all soils were aligned close to a virtual binary line between two apparent end member signatures (petrol and geogenic-Pb) suggesting that they are the major sources of Pb in the Egyptian environment. Soils with greater Pb concentrations (urban and industrial locations) displayed a significantly greater ratio of labile petrol-Pb to labile geogenic-Pb in comparison to less-contaminated soils. However, this difference was marginal (±5%) suggesting that historically emitted petrol-Pb has substantially mixed with geogenic-Pb into a common pool as a result of prolonged contact with soil. The proportion of petrol-Pb in fruits and leaf vegetables was significantly (P<0.005) greater than that of the associated soils suggesting preferential uptake of the more labile petrol-Pb as opposed to the relatively immobile geogenic-Pb. However, it is also possible that the major source of Pb intake by Egyptian consumers is extraneous Pb dust enriched with petrol Pb rather than systematic Pb via roots uptake., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Metal-salt amended soils (MA, n = 23), and historically-contaminated urban soils from two English cities (Urban, n = 50), were investigated to assess the effects of soil properties and contaminant source on metal lability and solubility. A stable isotope dilution method, with and without a resin purification step, was used to measure the lability of Cd, Cu, Ni, Pb and Zn. For all five metals in MA soils, lability (%E-values) could be reasonably well predicted from soil pH value with a simple logistic equation. However, there was evidence of continuing time-dependent fixation of Cd and Zn in the MA soils, following more than a decade of storage under air-dried conditions, mainly in high pH soils. All five metals in MA soils remained much more labile than in Urban soils, strongly indicating an effect of contaminant source on metal lability in the latter. Metal solubility was predicted for both sets of soil by the geochemical speciation model WHAM-VII, using E-value as an input variable. For soils with low metal solution concentrations, over-estimation of Cd, Ni and Zn solubility was associated with binding to the Fe oxide fraction while accurate prediction of Cu solubility was dependent on humic acid content. Lead solubility was most poorly described, especially in the Urban soils. Generally, slightly poorer estimation of metal solubility was observed in Urban soils, possibly due to a greater incidence of high pH values. The use of isotopically exchangeable metal to predict solubility is appropriate both for historically contaminated soils and where amendment with soluble forms of metal is used, as in toxicological trials. However, the major limitation to predicting solubility may lie with the accuracy of model input variables such as humic acid and Fe oxide contents where there is often a reliance on relatively crude analytical estimations of these variables. Trace metal reactivity in urban soils depends on both soil properties and the original source material; the WHAM geochemical model predicts solubility using isotopically exchangeable metal as an input., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Biochar, a by-product from the production of biofuel and syngas by gasification, was tested as a material for adsorption and fixation of U VI from aqueous solutions. A batch experiment was conducted to study the factors that influence the adsorption and time-dependent fixation on biochar at 20°C, including pH, initial concentration of U VI and contact time. Uranium (U VI ) adsorption was highly dependent on pH but adsorption on biochar was high over a wide range of pH values, from 4.5 to 9.0, and adsorption strength was time-dependent over several days. The experimental data for pH>7 were most effectively modelled using a Freundlich adsorption isotherm coupled to a reversible first order kinetic equation to describe the time-dependent fixation of U VI within the biochar structure. Desorption experiments showed that U VI was only sparingly desorbable from the biochar with time and isotopic dilution with 233 U VI confirmed the low, or time-dependent, lability of adsorbed 238 U VI . Below pH 7 the adsorption isotherm trend suggested precipitation, rather than true adsorption, may occur. However, across all pH values (4.5-9) measured saturation indices suggested precipitation was possible: autunite below pH 6.5 and either swartzite, liebigite or bayleyite above pH 6.5., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The rate of reactions between humic acid (HA) and iodide (I(-)) and iodate (IO3(-)) have been investigated in suspensions spiked with (129)I at concentrations of 22, 44 and 88 μg L(-1) and stored at 10 °C. Changes in the speciation of (129)I(-), (129)IO3(-) and mixed ((129)I(-) + (129)IO3(-)) spikes were monitored over 77 days using liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS). In suspensions spiked with (129)I(-) 25% of the added I(-) was transformed into organic iodine (Org-(129)I) within 77 days and there was no evidence of (129)IO3(-) formation. By contrast, rapid loss of (129)IO3(-) and increase in both (129)I(-) and Org-(129)I was observed in (129)IO3(-)-spiked suspensions. However, the rate of Org-(129)I production was greater in mixed systems compared to (129)IO3(-)-spiked suspensions with the same total (129)I concentration, possibly indicating IO3(-)I(-) redox coupling. Size exclusion chromatography (SEC) demonstrated that Org-(129)I was present in both high and low molecular weight fractions of the HA although a slight preference to bond with the lower molecular weight fractions was observed indicating that, after 77 days, the spiked isotope had not fully mixed with the native (127)I pool. Iodine transformations were modelled using first order rate equations and fitted rate coefficients determined. However, extrapolation of the model to 250 days indicated that a pseudo-steady state would be attained after ∼200 days but that the proportion of (129)I incorporated into HA was less than that of (127)I indicating the presence of a recalcitrant pool of (127)I that was unavailable for isotopic mixing., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Chemical extractants used to measure labile soil metal must ideally select for and solubilise the labile fraction, with minimal solubilisation of non-labile metal. We assessed four extractants (0.43 M HNO3, 0.43 M CH3COOH, 0.05 M Na2H2EDTA and 1 M CaCl2) against these requirements. For soils contaminated by contrasting sources, we compared isotopically exchangeable Ni, Cu, Zn, Cd and Pb (EValue, mg kg(-1)), with the concentrations of metal solubilised by the chemical extractants (MExt, mg kg(-1)). Crucially, we also determined isotopically exchangeable metal in the soil-extractant systems (EExt, mg kg(-1)). Thus 'EExt - EValue' quantifies the concentration of mobilised non-labile metal, while 'EExt - MExt' represents adsorbed labile metal in the presence of the extractant. Extraction with CaCl2 consistently underestimated EValue for Ni, Cu, Zn and Pb, while providing a reasonable estimate of EValue for Cd. In contrast, extraction with HNO3 both consistently mobilised non-labile metal and overestimated the EValue. Extraction with CH3COOH appeared to provide a good estimate of EValue for Cd; however, this was the net outcome of incomplete solubilisation of labile metal, and concurrent mobilisation of non-labile metal by the extractant (MExtEValue). The Na2H2EDTA extractant mobilised some non-labile metal in three of the four soils, but consistently solubilised the entire labile fraction for all soil-metal combinations (MExt ≈ EExt). Comparison of EValue, MExt and EExt provides a rigorous means of assessing the underlying action of soil chemical extraction methods and could be used to refine long-standing soil extraction methodologies., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

There is increasing interest in enhancing the micronutrient composition of cereals through fertilization. The aims of this study were (1) to determine the Se concentration of commercial beers retailing in the UK, and (2) to test if the transfer of Se, from biofortified grain to final beer product, is <10% under UK cultivation conditions, as seen previously under Mediterranean conditions. The Se concentration of 128 commercial beers was measured, using inductively coupled plasma-mass spectrometry (ICP-MS). The selenium content of commercial beers varied 6.5-fold, with beers originating from America having higher Se concentrations than those from Europe. Laboratory-scale brewing trials with isotopically-enriched (77)Se wheat, sampled from UK field-sites, showed that most (77)Se losses in the brewing process occurred during mashing (54%), with fermented beer containing ∼ 10% of the (77)Se initially present in the wheat grain. Total N values in wort and malt were positively correlated with the (77)Se content of the wheat grain., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The solubility, lability and fractionation of zinc in a range of calcareous soils from Peshawar, Pakistan were studied (18 topsoils and 18 subsoils). The lability (E-value) of Zn was assessed as the fraction isotopically exchangeable with (70)Zn(2+); comparative extractions included 0.005 M DTPA, 0.43 M HNO3 and a Tessier-style sequential extraction procedure (SEP). Because of the extremely low concentration of labile Zn the E-value was determined in soils suspended in 0.0001 M Na2-EDTA which provided reliable analytical conditions in which approximately 20% of the labile Zn was dissolved. On average, only 2.4% of soil Zn was isotopically exchangeable. This corresponded closely to Zn solubilised by extraction with 0.005 DTPA and by the carbonate extraction step (F1+F2) of the Tessier-style SEP. Crucially, although the majority of the soil CaCO3 was dissolved in F2 of the SEP, the DTPA dissolved only a very small proportion of the soil CaCO3. This suggests a superficial carbonate-bound form of labile Zn, accessible to extraction with DTPA and to isotopic exchange. Zinc solubility from soil suspended in 0.01 M Ca(NO3)2 (PCO2 controlled at 0.03) was measured over three days. Following solution speciation using WHAM(VII) two simple solubility models were parameterised: a pH dependent 'adsorption' model based on the labile (isotopically exchangeable) Zn distribution coefficient (Kd) and an apparent solubility product (Ks) for ZnCO3. The distribution coefficient showed no pH-dependence and the solubility model provided the best fit to the free ion activity (Zn(2+)) data, although the apparent value of log10 Ks (5.1) was 2.8 log units lower than that of the mineral smithsonite (ZnCO3)., (Copyright © 2015 Elsevier B.V. All rights reserved.)