Though an isotope approach could be beneficial for better understanding the biogeochemical cycle of gallium (Ga), an analogue of the monoisotopic element aluminum (Al), the geochemistry of Ga isotopes has not been widely elaborated. We developed a two-step method for purifying Ga from geological (biological) samples for precise measurement of Ga isotope ratio using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Ga was thoroughly separated from other matrix elements using two chromatographic columns loaded with AG 1-X4 and Ln-spec resin, respectively. The separation method was carefully calibrated using both synthetic and natural samples and validated by assessing the extraction yield (99.8 ± 0.8%, 2SD, n = 23) and the reproducibility (2SD uncertainty better than 0.05‰, n = 116) of the measured isotopic ratio (expressed as δ71Ga). The validation of the whole protocol, together with instrumental analysis, was confirmed by the investigation of the matrix effect, the result of a standard addition experiment, and the comparison of Ga isotope measurement on two mass spectrometers—Nu Plasma II and Neptune Plus. Although the measurements using the sample-standard bracketing (SSB) correction method on both instruments resulted in identical δ71Ga values for reference materials, the modified empirical external normalization (MEEN) method gave relatively better precision compared to SSB on Neptune. Our preliminary results showed large variation of δ71Ga (up to 1.83‰) for 10 standards, with higher values in industrially produced materials, implying potential application of Ga isotopes.

Practically all physical, chemical, and biological processes can induce mass-dependent fractionation of mercury (Hg) isotopes. A few special processes such as photochemical reduction of Hg(II) and photochemical degradation of methylmercury (MeHg) can produce mass-independent fractionation (MIF) of odd Hg isotopes (odd-MIF), which had been largely reported in variable natural samples and laboratory experiments, and was thought to be caused by either nuclear volume effect or magnetic isotope effect. Recently, intriguing MIF of even Hg isotopes (even-MIF) had been determined in natural samples mainly related to the atmosphere. Though photo-oxidation in the tropopause (inter-layer between the stratosphere and the troposphere) and neutron capture in space were thought to be the possible processes causing even-MIF, the exact mechanism triggering significant even Hg isotope anomaly is still unclear. Even-MIF could provide useful information about the atmospheric chemistry and related climate changes, and the biogeochemical cycle of Hg.同位素方法为研究汞生物地球化学循环开辟了新领域。除被大量报道并被实验验证的奇数汞同位素非质量分馏(Δ199Hg和Δ201Hg)外,自然样品中还发现了奇特的偶数汞同位素非质量分馏(Δ200Hg和Δ204Hg)。与奇数异常不同,偶数同位素非质量分馏的产生过程和机制尚不清楚。本文系统总结了当前关于偶数汞同位素异常的所有报道,详细讨论了发现偶数汞同位素异常的分析方法及其可能的产生过程和机理,并展望了其在汞生物地球化学循环及气候变化研究方面的应用前景。

The Hg isotopic signature may provide insight into tracking the sources and pathways of both airborne particulate matter (PM) and particle-bound Hg (PHg) in the atmosphere. However, separating and concentrating trace levels of PHg and accurately analyzing its isotope ratios remain a technical challenge. Here, we optimized a combustion-trapping dual-stage protocol specifically for the pre-concentration of Hg from a PM sample collected on a quartz fiber membrane (QFM) for high-precision Hg isotopic analysis. The protocol was validated by testing synthetic samples of varying concentrations and trapping solutions of different volumes, and by comparison with two conventional methods (acid digestion and column purification). Using the dual-stage protocol, an individual sample containing up to 570 ng of Hg can be combusted at programmed temperatures in an Hg-free O2 stream, and the volatilized gaseous Hg was trapped in a 5 mL acid (4 M HNO3 and 1.3 M HCl) mixture. The method results in a relatively lower procedural blank and quantitative recovery (99 ± 6%, 2SD, n = 90). Long-term measurements of three certified reference materials (CRM021, CRM024, and GBW07405) with complex matrices using the optimized protocol gave identical Hg isotopic ratios of both mass-dependent fractionation (MDF) and mass-independent fractionation (MIF), in agreement with the results obtained from the standard addition method. The protocol was applied to two PM2.5 samples collected on a 20.3 × 12.5 cm QFM. The result showed evident variations of both MDF and MIF, highlighting the importance of studying Hg isotopic compositions in PM of variable environments in order to fully understand the behaviors of Hg and its isotopes in the atmosphere.

The isotopic composition of mercury (Hg) is increasingly used to constrain the sources and pathways of this metal in the atmosphere. Though China has the highest Hg production, consumption and emission in the world, Hg isotope ratios are rarely reported for Chinese wet deposition. In this study, we examined, for the first time outside North America, both mass-dependent fractionation (MDF, expressed as δ202Hg) and mass-independent fractionation of odd (odd-MIF, Δ199Hg) and even (even-MIF, Δ200Hg) Hg isotopes in 15 precipitation samples collected from September 2012 to August 2013 in Guiyang (SW China). All samples displayed significant negative δ202Hg (–0.44 ∼ –4.27‰), positive Δ199Hg (+0.19 to +1.16‰) and slightly positive Δ200Hg (–0.01‰ to +0.20‰). Potential sources of Hg in precipitation were identified by coupling both MDF and MIF of Hg isotopes with a back-trajectory model. The results showed that local emission from coal-fired power plants and cement plants and western long-range transportation are two main contributing sources, while the contribution of Hg from south wind events would be very limited on an annual basis. The relatively lower Δ200Hg values in Guiyang precipitation may indicate a dilution effect by local sources and/or insignificant even-MIF in the tropopause contribution of this subtropical region. Our study demonstrates the usefulness of isotope fractionation, especially MIF for tracing sources and pathways of Hg in the atmosphere.

Practically all physical, chemical, and biological processes can induce mass-dependent fractionation of mercury (Hg) isotopes. A few special processes such as photochemical reduction of Hg(II) and photochemical degradation of methylmercury (MeHg) can produce mass-independent fractionation (MIF) of odd Hg isotopes (odd-MIF), which had been largely reported in variable natural samples and laboratory experiments, and was thought to be caused by either nuclear volume effect or magnetic isotope effect. Recently, intriguing MIF of even Hg isotopes (even-MIF) had been determined in natural samples mainly related to the atmosphere. Though photo-oxidation in the tropopause (inter-layer between the stratosphere and the troposphere) and neutron capture in space were thought to be the possible processes causing even-MIF, the exact mechanism triggering significant even Hg isotope anomaly is still unclear. Even-MIF could provide useful information about the atmospheric chemistry and related climate changes, and the biogeochemical cycle of Hg.

This study examines for the first time the characteristics of suspended particulate matter (SPM) and geochemical behaviors of major and trace elements during one single flood event of the Seine River, France. Source contribution, dilution by silicates and carbonates are the main scenarios consecutively occurring during the flood event, as can be inferred from the geochemical behaviors for major and trace elements. This study confirms the importance of flood events for the flux of materials transported by rivers to the ocean and emphasizes the need of systematic studies on the chemical variability of elements transported during flood events.

To trace the sources and pathways of Zn in hydrothermal systems, the Zn isotope compositions of seventeen water samples from eight thermal springs and six gas samples from two fumaroles from La Soufrière, an active volcano on Guadeloupe Island (French West Indies, FWI), were analyzed using a method adapted for purifying Zn from Fe- and SO4-enriched thermal solutions. The fumaroles are enriched in Zn 100 to 8000 times compared to the local bedrock and have isotopic compositions (δ66Zn values from +0.21‰ to +0.35‰) similar to or slightly higher than fresh andesite (+0.21‰). The enrichment of Zn in the thermal springs compared with the surface waters shows that Zn behaves as a soluble element during hydrothermal alteration but is significantly less mobile than Na. The δ66Zn values of most of the spring waters are relatively constant (approximately 0.70‰), indicating that the thermal springs from La Soufrière are enriched in heavy isotopes (i.e., 66Zn) compared to the host rocks (from −0.14‰ to +0.42‰). Only three thermal springs have lower δ66Zn values (as low as −0.43%). While the Zn in the fumaroles is essentially derived from magma degassing, which is consistent with a previous study on Merapi volcano (Toutain et al., 2008), we show that the Zn in the thermal springs is mainly derived from water–rock interactions. The 66Zn-enriched isotopic signature in most of the spring waters can be explained qualitatively by the precipitation at depth of sulfide minerals that preferentially incorporate the light isotopes. This agrees with the isotopic fractionation that was recently calculated for aqueous complexes of Zn. The few thermal springs with lower δ66Zn values also have low Zn concentrations, indicating the preferential scavenging of heavy Zn isotopes in the hydrothermal conduits.This study shows that unlike chemical weathering under surface conditions, hydrothermal alteration at high temperatures significantly fractionates Zn isotopes and enriches thermal waters in heavy Zn isotopes (e.g., 66Zn). Continental hydrothermal systems therefore constitute a source of heavy Zn isotopes to the oceans; this should be taken into account in the global oceanic budget of Zn.

The determination of fluxes and isotope compositions of Fe transported from continents to the ocean is essential for understanding global surface Fe cycle and its effect on oceanic biological productivity. Contrasting to non-polluted rivers, Fe isotope composition in rivers strongly affected by human activities is poorly constrained. In this contribution, we present the first Fe isotope data in suspended particulate matter (SPM) and dissolved load of the human-impacted Seine River (France). Iron concentrations and isotope compositions, together with major and trace element concentrations, were measured for two sample sets: (1) a geographic transect along the river from headwater to estuary, and (2) a temporal series of samples collected in Paris from 2004 to 2007. In the Seine River, Fe is mostly carried by SPM (average 99% of the total Fe) rather than dissolved load. The high Fe enrichment factor (1.40, relative to natural fluvial pre-historical and headwater sediments) and strong correlation between SPM Fe and Zn concentrations (r2 = 0.70, n = 30) demonstrate a strong anthropogenic Fe input. The Fe isotope compositions in SPM show a very small range (δ56Fe from −0.05‰ to 0.09‰) in spite of the large variations of Fe concentrations (from 1.78 to 4.17 wt.%) and are comparable to anthropogenic samples, suggesting that anthropogenic sources have similar Fe isotope composition to that of the natural background. In contrast, larger variations of Fe isotope compositions observed in the dissolved load (from −0.60‰ to 0.06‰) than that of SPM may provide a more promising means for tracing anthropogenic contributions to natural river systems. The δ56Fe and δ66Zn values of the dissolved loads are positively correlated (r2 = 0.62, n = 8), indicating a mixing between anthropogenic and natural end-members, enriched in light and heavy Fe isotopes respectively. Correlation between dissolved δ56Fe and DOC/Fe ratio (i.e. dissolved organic carbon/dissolved Fe concentrations) suggests that dissolved Fe of natural origin is mainly associated with organic colloids. The Fe compounds with low DOC/Fe ratio and δ56Fe values may correspond to anthropogenically-derived Fe-oxyhydroxide or sulfide colloids. Our study clearly demonstrates that polluted rivers transport an anthropogenic surplus flux of Fe that can be traced by coupling Fe and Zn isotopes. This surplus flux will fertilize the ocean and increase the primary productivity of phytoplankton, and thus may ultimately impact the global carbon cycle.

The Hg isotopic signature may provide insight into tracking the sources and pathways of both airborne particulate matter (PM) and particle-bound Hg (PHg) in the atmosphere. However, separating and concentrating trace levels of PHg and accurately analyzing its isotope ratios remain a technical challenge. Here, we optimized a combustion-trapping dual-stage protocol specifically for the pre-concentration of Hg from a PM sample collected on a quartz fiber membrane (QFM) for high-precision Hg isotopic analysis. The protocol was validated by testing synthetic samples of varying concentrations and trapping solutions of different volumes, and by comparison with two conventional methods (acid digestion and column purification). Using the dual-stage protocol, an individual sample containing up to 570 ng of Hg can be combusted at programmed temperatures in an Hg-free O2 stream, and the volatilized gaseous Hg was trapped in a 5 mL acid (4 M HNO3 and 1.3 M HCl) mixture. The method results in a relatively lower procedural blank and quantitative recovery (99 ± 6%, 2SD, n = 90). Long-term measurements of three certified reference materials (CRM021, CRM024, and GBW07405) with complex matrices using the optimized protocol gave identical Hg isotopic ratios of both mass-dependent fractionation (MDF) and mass-independent fractionation (MIF), in agreement with the results obtained from the standard addition method. The protocol was applied to two PM2.5 samples collected on a 20.3 × 12.5 cm QFM. The result showed evident variations of both MDF and MIF, highlighting the importance of studying Hg isotopic compositions in PM of variable environments in order to fully understand the behaviors of Hg and its isotopes in the atmosphere.