A combination of sequential extraction with stable isotope ratio measurements of Se might offer new insights into biogeochemical processes governing Se turnover in soils. Therefore, we determined the Se partitioning among three operationally defined sequential extracts (0.1 mol L"' KjHPO^-KHjPO^ at pH 7,0.05 mol L"' NaOH, cone.HNOj) and the stable isotope ratios of total Se (^''^''^Se values) in 10 topsoils under 5 different land uses (alluvial grasslands, forests, house gardens, parks, and roadside grassland) from the city of Bayreuth (ca. 73,000 inhabitants) in Germany. Furthermore, we detetmined S and SO^^" concentrations and stable isotope ratios of total S (ä'^S values) to support our interpretation ofthe Se concentrations and isotope ratios because of the chemical similarity of Se and S. All topsoils had low total Se concentrations (0.09-0.52 mg kg~ ). The latgest conttibution to total Se was extracted with NaOH compdsing up to 42%,which is thought to be associated with organic matter and metal oxides. The 5 ' Se values of total Se in the topsoils were close to the bulk Earth composition with an average J82//65Ç value of -0.03 + SD 0.38%c suggesting that there was no or linle Se isotope fractionation in soil. We attribute the small isotope fractionation to the low bioavailability of Se as a consequence ofthe presence of Fe oxides (adsorbing the dominating Se(IV) forms strongly), organic matter, and SO^ (prevents biouptake ofthe Se(IV) forms) in the study soils. Small Se isotope fractionations of-0.59 to -0.35%o in mainly forest soils and of 0.26 to 0.45%o in mainly alluvial soils were presumably caused by soil/plant-recycling and Se contamination by river water, respectively In spite ofthe similarities in the assimilation of S and Se by organisms, the total S and Se isotope ratios in soil were not correlated. Our results demonstrate that Se in urban soils developed ftom Se-poor substrates is minimally cycled through the biosphere likely because of low bioavailability and competition with SO, 2-

The natural abundance of stable Se isotopes may reflect sources and formation conditions of methylated Se. We aimed at (1) quantifying the degree of methylation of selenate [Se(VI)] and (hydro)selenite [Se(IV)] by the fungus Alternaria alternata at pH 4 and 7 and (2) determining the effects of these different Se sources and pH values on 82Se/76Se ratios (δ82/76Se) in methylselenides. Alternaria alternata was incubated with Se(VI) and Se(IV) in closed microcosms for 11-15 days and additionally with Se(IV) for 3-5 days at 30 °C. We determined Se concentrations and δ82/76Se values in source Se(VI) and Se(IV), media, fungi, and trapped methylselenides. In Se(VI) incubations, methylselenide volatilization ended before the 11th day, and the amounts of trapped methylselenide were not significantly different among the 11-15 day incubations. In 11-15 days, 2.9-11% of Se(VI) and 21-29% of Se(IV) were methylated, and in 3-5 days, 3-5% of Se(IV) was methylated. The initial δ82/76Se values of Se(VI) and Se(IV) were -0.69±SD 0.07‰, and -0.20±0.05‰, respectively. The δ82/76Se values of methylselenides differed significantly between Se(VI) (-3.97‰ to -3.25‰) and Se(IV) (-1.44‰ to -0.16‰) as sources after 11-15 days of incubation; pH had little influence on δ82/76Se values. Thus, the δ82/76Se values of methylselenide indicate the source species of methylselenides used in this study. The strong isotope fractionation of Se(VI) is probably attributable to the different reduction steps of Se(VI) to Se(-II) which were rate-limiting explaining the low methylation yields, but not to the methylation itself. The shorter incubation of Se(IV) for 3-5 days showed a large Se isotope fractionation of at least -6‰ before the biomethylation reaction reached its end. This initial Se isotope fractionation during methylation of Se(IV) is much larger than previously published.

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Selenium poisoning is a significant health problem in parts of Punjab, India, which is an area of intense agricultural productivity. To determine the complex soil dynamics that control distribution of Se in this area, we measured concentrations and δ(82/76)Se of bulk Se and individual Se pools in four soil profiles. This was compared against δ(82/76)Se of crops and groundwater used for irrigation. The isotopic composition of bulk Se and component Se pools reveal spatial heterogeneity. The bulk δ(82/76)Se show progressively lower values with increasing soil depth indicating the preferential migration of isotopically lighter Se downward through the soil profile. The δ(82/76)Se of water-soluble Se is isotopically heavier than δ(82/76)Se of adsorbed Se, suggesting Se isotope fractionation by reduction prior to scavenging by reactive minerals in the soil. The organically bound Se is isotopically lighter than water-soluble Se and correlates with the C/N ratio at different soil depths. Thus, Se immobilization by redox cycling controls the biogeochemical Se cycle in the soil. Se isotope ratios help to trace biochemical processes of Se in agricultural seleniferous soils and provide an important assessment for better soil management mitigating Se concentrations of ecotoxicological levels.

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Urine metallomics as potential diagnostic tool for PDAC, one of the deadliest types of cancer.

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The disruption of Zn homeostasis has been linked with breast cancer development and progression. To enhance our understanding of changes in Zn homeostasis both inside and around the tumour microenvironment, Zn concentrations and isotopic compositions (δ66Zn) were determined in benign (BT) and malignant (MT) tumours, healthy tissue from reduction mammoplasty (HT), and histologically normal tissue adjacent to benign (NAT(BT)) and malignant tumours (NAT(MT)). Mean Zn concentrations in NAT(BT) are 5.5 μg g−1 greater than in NAT(MT) (p = 0.00056) and 5.1 μg g−1 greater than in HT (p = 0.0026). Zinc concentrations in MT are 12.9 μg g−1 greater than in HT (p = 0.00012) and 13.3 μg g−1 greater than in NAT(MT) (p < 0.0001), whereas δ66Zn is 0.17‰ lower in MT than HT (p = 0.017). Benign tumour Zn concentrations are also elevated compared to HT (p = 0.00013), but are not significantly elevated compared to NAT(BT) (p = 0.32). The δ66Zn of BT is 0.15‰ lower than in NAT(BT) (p = 0.045). The similar light δ66Zn of BT and MT compared to HT and NAT may be related to the isotopic compensation of increased metallothionein (64Zn-rich) expression by activated matrix metalloproteinase (66Zn-rich) in MT, and indicates a resultant 66Zn-rich reservoir may exist in patients with breast tumours. Zinc isotopic compositions thus show promise as a potential diagnostic tool for the detection of breast tumours. The revealed differences of Zn accumulation in healthy and tumour-adjacent tissues requires additional investigation.