Selenium: An Element of Life Essential for Thyroid Function

Selenium (Se), a microelement essential for life, is critical for homeostasis of several critical functions, such as those related to immune–endocrine function and signaling transduction pathways. In particular, Se is critical for the function of the thyroid, and it is particularly abundant in this gland. Unfortunately, Se deficiency is a very common condition worldwide. Supplementation is possible, but as Se has a narrow safety level, toxic levels are close to those normally required for a correct need. Thus, whether the obtaining of optimal selenium concentration is desirable, the risk of dangerous concentrations must be equally excluded. This review addressed the contribution by environment and food intake on Se circulating levels (e.g., geographical factors, such as soil concentration and climate, and different quantities in food, such as nuts, cereals, eggs, meat and fish) and effects related to its deficiency or excess, together with the role of selenium and selenoproteins in the thyroid pathophysiology (e.g., Hashimoto’s thyroiditis and Graves’ disease).

Microplastic fibers influence Ag toxicity and bioaccumulation in Eisenia andrei but not in Enchytraeus crypticus

Microplastic fibers (MF) are released from synthetic textiles during washing and end up in the wastewater. Similarly, silver nanoparticles (AgNP), incorporated in textiles as antimicrobial agents, are released in washing machines, also reaching the wastewater treatment plants. Therefore, both MF and AgNP co-exist in the environment, and enter the soil compartment mainly via the application of biosolids. Yet, the combined effect of MF and AgNP has not been studied. Here, we assessed the effects of polyester MF (0.01% DW) on the toxicity of AgNP (32, 100, 320, 1000, 3200 mg Ag/kg) and AgNO3 (12.8, 32, 80, 200, 500 mg Ag/kg) to the earthworm Eisenia andrei and the enchytraeid Enchytraeus crypticus. The exposure to MF caused a decrease in the number of juveniles and changed the biochemical composition of earthworms. Moreover, the presence of MF increased the toxicity of AgNP to earthworm reproduction (EC50 = 165 mg Ag/kg) when compared to AgNP exposure alone (EC50 = 450 mg Ag/kg), but did not alter the toxicity of AgNO3 (EC50 = 40 mg Ag/kg). For enchytraeids, no significant difference in Ag toxicity could be detected when MF was added to the soil for both AgNP and AgNO3. Overall, Ag bioaccumulation was not affected by MF, with the exception of a decrease in earthworm body concentration at the highest Ag soil concentration (3200 mg Ag/kg). Our results suggest that the presence of MF in the soil compartment may be a cause of concern, and that the joint exposure to Ag may be deleterious depending on the Ag form, organism and endpoint. The present work provides the first evidence that a realistic MF concentration in soil lowers AgNP concentration necessary to provoke reproductive impairment in earthworms. The influence of MF on risk assessment of AgNP should be considered.

Risk Factors for Environmental Pollution with Dioxin-Containing Compounds

Introduction. It has been demonstrated that the use of 2,4-D herbicide contaminates the environment with polychlorinated compounds, including dioxins. Additional risk factors for population health and the environment include climatic conditions of Siberia, processes of translocation of compounds from soil to plants, their ability to reach the human body along trophic chains and to have a toxic effect. The objective of this study was to analyze the behavior of the 2,4-D herbicide and dioxins in the environment and to justify health risk factors. Materials and methods. We used the method of gas chromatography-mass spectrometry that combines high efficiency of separation of impurities, the possibility of determining their molecular composition, selectivity of recording, and high sensitivity. We used a chromatographic method to determine residual amounts of the 2,4-dichlorophenoxyacetic acid amine salt (2,4-D) in soil, feed, and food of plant and animal origin. The calculation of average and statistical errors of indicators was performed using t-test in MS Excel. Results. Contamination of water of open reservoirs of the Irkutsk Region with the 2,4-D herbicide amine salt was found in concentrations as high as 7.7 μg/L with a positive sample count of 49%. In spring and summer, the water of open reservoirs is also polluted. In soils, the 2,4-D amine salt is immobile, concentrated in the surface layer at the level of 0.42–0.37 mg/kg. The maximum total soil concentration of dioxins reached 1,479 ng/kg exceeding the maximum permissible soil concentration of dioxins by 306 times. The maximum concentration of dioxins in feed was found at the end of the growing season (317–322 ng/kg). Dioxins accumulate in fat-containing food; thus, measured dioxin concentrations in butter averaged 680.6 ng/kg demonstrating a 10-fold excess of the permissible level. The estimated daily intake of dioxins with food can be as high as 26.2 pg/kg, which is 2.6 times higher than the permissible daily dose. We conducted the environmental and medico-hygienic analysis of outcomes of using the effective herbicide that poses a serious danger to human health due to the possibility of dioxin formation. We identified risk factors and substantiated the daily dose of dioxins for humans as a temporary value.

Assessment of plants for phytoremediation of hydrocarbon-contaminated soils in the Sudd Wetland of South Sudan

Hydrocarbon contaminants have become a global concern due to their long-term adverse effects on soil ecosystems and human health. Successful implementation of phytoremediation to clean up hydrocarbon contaminants requires the identification of the most effective remediation plant species. Twelve native plant species of the Sudd Wetland in South Sudan were evaluated for their potential application as phytoremediators. The treatments included six total petroleum hydrocarbon (TPH) concentrations of 0, 25, 50, 75, 100 and 125 g/kg soil. The twelve native plant species tested were: Sorghum arundinaceum Desv., Oryza longistaminata A. Chev. & Roehrich, Hyparrhenia rufa Nees, Abelmoschus ficulneus L., Gossypium barbadense L., Nicotiana tabacum L., Sorghum bicolour L. Moench, Eleusine coracana Gaertn., Capsicum frutescens L., Zea mays L., Tithonia diversifolia Hemsl. and Medicago sativa L. Significant differences in phytoremediation rates were observed amongst the treatments with exception of the 125 g/kg soil concentration of hydrocarbon that was lethal to all the plant species. Over 50% TPH reduction in the 75 g/kg soil concentration was observed in contaminated soil phytoremediation in H. rufa, G. barbadense, O. longistaminata, T. diversifolia and S. arundinaceum, making them potential phytoremediators of hydrocarbon-contaminated soil in the Sudd-Wetland of South-Sudan.

Hypothetical Thresholds for Effects of Platinum Group Elements

The platinum-group elements are rhodium, ruthenium, palladium, osmium, iridium, and platinum. Together with rhenium and gold they form the highly siderophilic (“iron-loving”) elements. These are poorly known with respect to toxicity and ecotoxicity. The mobilization by man of the eight metals is about 100 times to 1 million times the natural mobilization. Mean soil concentrations in Europe may now be more than doubled for gold, rhenium and rhodium. The objective of the current work was to enable a preliminary assessment of the consequences of such high environmental levels. Thresholds for ecological effects found in the literature were divided by the element’s mean soil concentration and plotted against group and period in the periodic system. Thresholds for health effects were correspondingly divided by the mean dietary intake of the element over large population groups. For health effects, an upper limit of intake is commonly used. This was shown to be about 4 times the mean normal intake for most period 4 elements. For other periods, occupational exposure thresholds entail upper limits of intake in µg/day of: Ru 18, Rh 8, Pd 17, Re 60, Os 15, Ir 4, Pt 20 and Au 160. For ecological effects, the no effect thresholds for period 4 were 1-5 times the soil concentrations. Very scarce data suggest higher relative thresholds for periods 5 and 6. The current high contaminations of European soil by Rh and possibly Pd may be of concern. Since the estimates of risks are uncertain, further research is warranted.

Soil–atmosphere exchange of carbonyl sulfide in a Mediterranean citrus orchard

Carbonyl sulfide (COS) is used as a tracer of CO2 exchange at the ecosystem and larger scales. The robustness of this approach depends on knowledge of the soil contribution to the ecosystem fluxes, which is uncertain at present. We assessed the spatial and temporal variations in soil COS and CO2 fluxes in a Mediterranean citrus orchard combining surface flux chambers and soil concentration gradients. The spatial heterogeneity in soil COS exchange indicated net uptake below and between trees of up to 4.6 pmol m−2 s−1 and net emission in sun-exposed soil between rows of up to 2.6 pmol m−2 s−1, with an overall mean uptake value of 1.1±0.1 pmol m−2 s−1. Soil COS concentrations decreased with soil depth from atmospheric levels of ∼450 to ∼100 ppt at 20 cm depth, while CO2 concentrations increased from ∼400 to ∼5000 ppm. COS flux estimates from the soil concentration gradients were, on average, -1.0±0.3 pmol m−2 s−1, consistent with the chamber measurements. A soil COS flux algorithm driven by soil moisture and temperature (5 cm depth) and distance from the nearest tree, could explain 75 % of variance in soil COS flux. Soil relative uptake, the normalized ratio of COS to CO2 fluxes was, on average, -0.4±0.3 and showed a general exponential response to soil temperature. The results indicated that soil COS fluxes at our study site were dominated by uptake, with relatively small net fluxes compared to both soil respiration and reported canopy COS fluxes. Such a result should facilitate the application of COS as a powerful tracer of ecosystem CO2 exchange.