Biological fractionation of lithium isotopes by cellular Na+/H+ exchangers unravels fundamental transport mechanisms.

Lithium (Li) has a wide range of uses in science, medicine, and industry, but its isotopy is underexplored, except in nuclear science and in geoscience. 6Li and 7Li isotopic ratio exhibits the second largest variation on earth's surface and constitutes a widely used tool for reconstructing past oceans and climates. As large variations have been measured in mammalian organs, plants or marine species, and as 6Li elicits stronger effects than natural Li (∼95% 7Li), a central issue is the identification and quantification of biological influence of Li isotopes distribution. We show that membrane ion channels and Na+-Li+/H+ exchangers (NHEs) fractionate Li isotopes. This systematic 6Li enrichment is driven by membrane potential for channels, and by intracellular pH for NHEs, where it displays cooperativity, a hallmark of dimeric transport. Evidencing that transport proteins discriminate between isotopes differing by one neutron opens new avenues for transport mechanisms, Li physiology, and paleoenvironments.

"Non-traditional" stable isotopes applied to the study of trace metal contaminants in anthropized marine environments.

The advent of Multicollector ICP-MS inaugurated the analysis of new metal isotope systems, the so-called "non-traditional" isotopes. They are now available tools to study geochemical and ecotoxicological aspects of marine metal contamination and hence, to push the frontiers of our knowledge. However, such applications are still in their infancy, and an accessible state-of-the-art describing main applications, obstacles, gaps, and directions for further development was missing from the literature. This paper fills this gap and aims to encourage the marine scientific community to explore the contributions of this newly available information for the fields of chemical risk assessment, biomonitoring, and trophic transfer of metal contaminants. In the current "Anthropocene" epoch, metal contamination will continue to threaten marine aquatic ecosystems, and "non-traditional" isotopes can be a valuable tool to detect human-induced changes across time-space involving metal contaminants, and their interaction with marine biota.

The impact of anthropogenic inputs on lithium content in river and tap water.

The use of lithium (Li) has dramatically increased during the last two decades due to the proliferation of mobile electronic devices and the diversification of electric-powered vehicles. Lithium is also prescribed as a medication against bipolar disorder. While Li can exert a toxic effect on living organisms, few studies have investigated the impact of anthropogenic inputs on Li levels in the environment. Here we report Li concentrations and Li isotope compositions of river, waste and tap water, and industrial products from the metropolitan city of Seoul. Results show that the large increase in population density in Seoul is accompanied by a large enrichment in aqueous Li. Lithium isotopes evidence a major release from Li-rich materials. Water treatment protocols are also shown to be inefficient for Li. Our study therefore highlights the need for a global Li survey and adequate solutions for minimizing their impact on ecosystems and city dwellers.

Impact of climate change and human activity on soil landscapes over the past 12,300 years.

Soils are key to ecosystems and human societies, and their critical importance requires a better understanding of how they evolve through time. However, identifying the role of natural climate change versus human activity (e.g. agriculture) on soil evolution is difficult. Here we show that for most of the past 12,300 years soil erosion and development were impacted differently by natural climate variability, as recorded by sediments deposited in Lake Dojran (Macedonia/Greece): short-lived ( < 1,000 years) climatic shifts had no effect on soil development but impacted soil erosion. This decoupling disappeared between 3,500 and 3,100 years ago, when the sedimentary record suggests an unprecedented erosion event associated with the development of agriculture in the region. Our results show unambiguously how differently soils evolved under natural climate variability (between 12,300 and 3,500 years ago) and later in response to intensifying human impact. The transition from natural to anthropogenic landscape started just before, or at, the onset of the Greek 'Dark Ages' (~3,200 cal yr BP). This could represent the earliest recorded sign of a negative feedback between civilization and environmental impact, where the development of agriculture impacted soil resources, which in turn resulted in a slowdown of civilization expansion.

Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa.

Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth's climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region.

Natural variations of lithium isotopes in a mammalian model.

Despite lithium's extensive clinical applications, the cellular and molecular basis for the therapeutic effects remains to be elucidated. The large difference in mass between the two lithium isotopes ((6)Li and (7)Li) has prompted biochemists to explore the metabolism of Li by using pure (6)Li and (7)Li labeled drugs. However, experiments were carried out at very high Li concentrations, which did not reflect natural conditions. In the present study, we consider, for the first time, the natural variations of the (7)Li/(6)Li ratio in the organs and body fluids of an animal model, sheep. Each organ seems to be characterized by a specific Li isotope composition. So far, the range of the (7)Li/(6)Li ratio in the sheep body, expressed as δ permil variations relative to the L-SVEC standard (δ(7)Li), is about 40‰, between muscles (∼40‰) and kidney (∼0‰). Relative to a dietary δ(7)Li value of ∼+17‰, serum, red blood cells, muscle, liver, brain and kidney have a (7)Li enrichment of -12‰, -14‰, +22‰, +5‰, -3‰ and -15‰, respectively. The Li isotope composition is likely to be fractionated during intestinal absorption, with a greater absorption of (6)Li relative to (7)Li. According to previous conclusions obtained with (6)Li and (7)Li labeled chemicals, (6)Li appears to diffuse into erythrocytes faster than does (7)Li. However, this does not hold for myocytes and hepatocytes, because these two tissues have a higher δ(7)Li level than serum. Purely diffusive isotopic fractionation would leave all organs (7)Li-depleted relative to the serum, which is not the case, suggesting that active, molecule-specific, isotopic fractionation occurs in the body. Our preliminary results suggest that natural Li isotope variations can shed light on its regulation in the body, being active or passive.