Osmium in environmental samples from Northeast Sweden. Part I. Evaluation of background status

Osmium isotope geochemistry of steel plant emissions using tree bark biomonitoring

We report for the first time the Os isotopic composition of tree bark samples from a steel town. Osmium concentrations and ¹⁸⁷Os/¹⁸⁸Os isotopic ratios of ashed bark samples range from 1.40 to 24 ppt and 0.70 to 1.54, respectively, with the lowest ¹⁸⁷Os/¹⁸⁸Os recorded in samples close to the steel plant. Compositional variations in the bark samples can be explained by mixing between at least two sources with different Os isotopic signatures: a radiogenic source consistent with crust-derived materials and a relatively less radiogenic source consistent with mantle-derived chromite. The exact origin of the radiogenic Os component cannot be constrained, as background signatures and crustal materials used in the steel industry (e.g., coal and iron ore) likely have overlapping radiogenic signatures. Cr shows a similar distribution pattern to Os, indicating that both metals have a common origin, which provides further evidence that the Os budget in the bark samples is controlled primarily by the chromite used in the steel manufacturing. This study shows that Os isotopes are an effective tool for tracing steel production-related emissions.

Anthropogenic Osmium in Macroalgae from Tokyo Bay Reveals Widespread Contamination from Municipal Solid Waste

Human activity is influencing the global osmium cycle, driving the Os isotopic composition (¹⁸⁷Os/¹⁸⁸Os) of the hydrosphere and associated sedimentary material to lower values. Here, we present the Re and Os abundance and isotope systematics of macroalgae, a proxy for seawater, from Tokyo Bay to elucidate the potential sources of anthropogenic Os to the Pacific Ocean. Macroalgae from the Uraga Channel, which connects Tokyo Bay to the Pacific Ocean, record relatively low Os abundances (∼10.1 pg/g) and an ¹⁸⁷Os/¹⁸⁸Os of ∼0.9, indicative of surface ocean seawater. Contrastingly, macroalgae within the bay closest to central Tokyo record the highest Os abundances (∼22.8 pg/g) and lowest ¹⁸⁷Os/¹⁸⁸Os values (∼0.47), suggesting contamination from human activity. To determine the source of anthropogenic Os, we have developed the first Os emission inventory, based on the East Asian Air Pollutant Emission Grid database (EAGrid2010). The close relationship (R² = 0.67 and p-value = <0.05) between Os inventories and macroalgal data suggests that municipal solid waste incinerators (MSWIs) are the dominant source of Os to Tokyo Bay. Projections for Japan estimate that 26_-18⁺³⁸ ng Os/m²/yr is released from MSWI smokestacks, leading to a concentration in precipitation of 26_-18⁺³⁸ fg/g, identifying MSWIs as a major contributor of anthropogenic Os to the hydrological cycle.

Seasonal shift of diet in bank voles explains trophic fate of anthropogenic osmium?

Diet shifts are common in mammals and birds, but little is known about how such shifts along the food web affect contaminant exposure. Voles are staple food for many mammalian and avian predators. There is therefore a risk of transfer of contaminants accumulated in voles within the food chain. Osmium is one of the rarest earth elements with osmium tetroxide (OsO₄) as the most toxic vapor-phase airborne contaminant. Anthropogenic OsO₄ accumulates in fruticose lichens that are important winter food of bank voles (Myodes glareolus). Here, we test if a) anthropogenic osmium accumulates in bank voles in winter, and b) accumulation rates and concentrations are lower in autumn when the species is mainly herbivorous. Our study, performed in a boreal forest impacted by anthropogenic osmium, supported the hypotheses for all studied tissues (kidney, liver, lung, muscle and spleen) in 50 studied bank voles. In autumn, osmium concentrations in bank voles were even partly similar to those in the graminivorous field vole (Microtus agrestis; n=14). In autumn but not in late winter/early spring, osmium concentrations were generally negatively correlated with body weight and root length of the first mandible molar, i.e. proxies of bank vole age. Identified negative correlations between organ-to-body weight ratios and osmium concentrations in late winter/early spring indicate intoxication. Our results suggest unequal accumulation risk for predators feeding on different cohorts of bank voles.

Osmium in environmental samples from Northeast Sweden. Part II. Identification of anthropogenic sources

Osmium (Os) concentrations and (187)Os/(188)Os isotope abundance ratios measured in epiphytic lichens from Northeast Sweden have been used for the identification of anthropogenic emission sources of this element. Based on isotope abundance ratios and similarities in spatial distributions between Os and chromium, smelters operated on chromium ores from Kemi deposits have shown to be the most important factor affecting the airborne Os burden in the region. The extent of the exposure is reflected by lichen concentrations near the source exceeding those from remote areas by a factor of 1000. Contributions from metal foundries processing iron, copper, lead and zinc ores can also be seen, though, because of lower Os concentrations in the feedstock, on a considerably lower scale. Masked by these industrial emissions in the studied area, the impact of Os originating from automotive catalytic converters cannot be resolved at present.