Methodology for Hg determination in foliar samples
Moving to Slovenia has been exciting and full of adventure. Despite most of the events happening through online platforms, I did have the opportunity to visit some of the most beautiful regions of Slovenia as part of the field campaigns to study the role of forest ecosystems in the exchange of Hg between the atmosphere and terrestrial compartments. One important aspect of this was the validation of the methodology for Hg determination in foliar samples which is needed for the estimation of the uncertainties associated with different sampling approaches and sample preparation techniques. For this reason, field visits were carried out for the collection of foliar samples from two contrasting forest sites in Slovenia. We visited Idrija which has an extensive history of mercury mining. Samples were collected from forest site adjacent to the smelter plant having a 500-year-old mining history and which is also inscribed on UNESCO World Heritage List in 2012 for the same reason.
Foliage samples were collected from different locations on the tree crown and stored following an approved protocol. Similar sample collection was also done in Ljubljana city which is relatively less contaminated and has no reported major Hg point source. Following their transport to the laboratory, foliage samples were treated in several ways during their preparation for the determination of Hg content among other elements. Apart from this, the seasonal variation in foliar Hg concentrations is also being studied at two additional sites. Whereas the Salonit Anhovo cement factory remains at the center of attention mainly due to the potential risk of Hg emission into the surrounding environment, Iskrba is considered a remote site located in the southern part of Slovenia far away from any major Hg source. These visits are providing the necessary experience to understand the key role of forest ecosystems in global Hg biogeochemical cycle.
Another important aspect under study is how some of the potential explanatory variables (predictors) explain the spatial patterns of Hg uptake by forest ecosystems on a global scale. Using available global datasets and with the help of advanced machine learning tools, the aim is to predict future scenarios of the intensity as well as the spatial patterns of Hg exchange between the atmosphere and terrestrial compartments.
In addition to this, I also enjoy working in the laboratory, helping my colleagues in their work, and getting trained for the determination of THg and MeHg in water samples at the Mercury lab. We are also maintaining the Tekran speciation unit in Ljubljana and I am confident that the upcoming secondments and other networking events planned in the GMOS-Train project will be yet another opportunity to learn diverse set of skills and enhance my capacity as a researcher.
By Saeed Waqar Ali (ESR 9)
70 scientists studied volcanism, the water column and ecosystems on the largest submarine eruption ever observed
During April and May GEOFLAMME oceanographic campaign took place in the vicinity of Mayotte Island in the western Indian Ocean, where nearly 70 scientists from different institutes and laboratories board N/O Pourquoi pas? to study the interactions between volcanism, the water column and ecosystems on the largest submarine eruption ever observed, off the island of Mayotte. The multidisciplinary scientific research study of this major eruption was performed by carrying out in-situ observations and sampling (ROV, CTD, dredges and corers) and analyzes (petrology, chemistry, biochemistry) of rocks, pure fluids and the water column combined with high resolution maps, and reconstructions of volcanic, tectonic structures and fluid outlets (with ROV and AUV). ESR6 and the Ifremer LBCM Nantes mercury team participated in the campaign to investigate mercury dynamics associated to volcanic and pelagic processes. On-board analysis of Total Hg and Dissolved gaseous Hg, as well as suspended particles (McLane pump), water and fluids samplings (for MMHg analysis on land) were performed in order to acquire a baseline (dissolved / particulate) Hg data for the water column and for the acquisition of new knowledge on the volcano-mercury link from contents in pure fluids, diffusions, and the near and distal plume.
Fig1. ROV operation for the detection of fluid outlets and CO2 hydrates sites
Later this year during July, ESR6 and the Ifremer LBCM Nantes mercury team also participated in a sampling campaign for PoNutELA project at Étang du Prevost, a model lagoon where the sediment constitutes the main reservoir of nutrients and chemical pollutants brought by the watersheds. The main objective of this project is to study the impact of hypoxia on the fate of pollutants and nutrients in sediments in Mediterranean Lagoon ecosystems. For this campaign, an upgraded SUSANE sampling device was used to sample more accurately the gradient of dissolved Hg speciation and particulate data in the water column during the minimum and maximum oxygen concentrations in order to characterize the impact of variations in oxygen concentrations in the water column on transfers of chemical species at the water-sediment interface.
By Isabel Garcia (ESR 6)
Field Campaign at Askö Laboratoriet and onboard R/V Electra
Alina (ESR 5) and Sonja (ESR 7) conducted a field campaign in the Baltic Sea in June of this year. With the support of Charlotte (ESR 8) and two post-docs from Stockholm University they carried out three day-cruises onboard the R/V Electra af Askö. Along a transect from the Trosaån estuary (HF) to Landsort Deep (BY31), they sampled six stations around Stockholm Archipelago. The transect covers waters with distinct biogeochemical characteristics, from anthropogenically influenced water near a wastewater treatment plant outlet to the deepest point of the Baltic Sea (Landsort Deep). The semi-enclosed Baltic Sea is subject to a strong vertical salinity gradient. This gradient leads to a stratification of the water column resulting in anoxic conditions below the halocline, which favor microbial mercury (Hg) methylation. The Baltic Sea is affected by multiple stressors, such as large nutrient inputs, chemical pollution, warming, O2 depletion, acidification, and invasive species. Besides the ecological relevance, these bear economic and health hazards. Related to these pressures, an expansion of the oxygen depleted zones has been predicted, which could potentially result in elevated MeHg concentrations in seafood, the main threat of Hg poisoning to the general public. Additionally, climate and land use change can increase the amount of Hg entering the marine environment via rivers and surface runoff..
The overall goal of the study is to test the hypothesis that Hg entering the sea from land is mainly unavailable for methylation and biological uptake. In total, they took almost 900L of brackish water from 15 CTD casts, various sediment cores and phytoplankton samples to better understand the biotic and abiotic conditions along the transect. Water samples were not only taken for Hg speciation analysis, but also to analyze a large variety of parameters, such as FDOM, DOC, TOC, nitrate, phosphate, sulfate and thiols. Another important question is what role organic matter and its origin plays for Hg transformations in the water column. Therefore, Sonja extracted DOM from over 400 L of seawater. In addition, Alina carried out incubation experiments to constrain mercury (de-)methylation rates using isotopically enriched tracers in well-oxygenated surface waters and the anoxic bottom water of Landsort Deep.
Looking back at the experience, Alina sums up: “I enjoyed the field campaign with the great infrastructure provided, good company and perfect weather conditions”. Sonja has a similarly positive impression of the collaboration and says: “It was a great experience to plan and conduct our own field campaign under these conditions. Now I am super excited for the results!”.
While Alina and Sonja are now diligently working on the measurements and experiments in the laboratories of the universities of Stockholm and Pau, Charlotte is on her way to another research adventure in the north of Sweden.
Carbon and mercury stable isotopes fractionation during aqueous MeHg photoreduction
Luisa (ESR 3) worked in 7 photoreduction experiments with different conditions to study Hg and C stable isotopes. The relevant results were presented at the Goldschmidt conference in June under the title “ Carbon and mercury stable isotopes fractionation during aqueous MeHg photoreduction” in the section “Towards a better understanding of mercury dynamics within and between land, atmosphere and ocean systems to support the effectiveness evaluation of the Minamata Convention”. Still, some clues are missing and the C isotope study resulted be more complicated than expected initially. To finish the photo degradation study and complete the C isotope analysis, 3 more experiments were planned for the months of August and September. And then that’s it, no more colored waste experiments.
For the month of November and with great excitement, Luisa is also getting ready for 1 month secondment in Sweden at the Stockholm University, with Dr. Sofy Jonsson and Sonja Gindorf (ESR7). This time to work, learn and explore the abiotic methylation of mercury under lab controlled condition instead of the degradation of the MeHg. Which are the best abiotic methylation methods? How to avoid the formation of Dimethylmercury (DMHg)? It’s DMHg a compound of interest in our research? Could we find a way to measure C isotopes in DMHg? How does the isotopic composition of C change from the reactants to the final product? Many more questions to answer in the search for fingerprints to point out the MeHg origin.
Atmospheric mercury in the tropical Bolivian Andes and Indian Ocean
I invested most of the first year in the GMOS-train in the data analysis of atmospheric mercury measured at two southern hemisphere sites: Chacaltaya mountain in the tropical Bolivian Andes and Maïdo observatory in the tropical Indian Ocean.
I was very lucky that the collaboration with my supervisors and colleagues worked smoothly and pleasantly, even in times where in-person discussions and meetings were in short supply. In this productive work environment, I managed to get the first paper on atmospheric mercury at Chacaltaya published (“Seasonal patterns of atmospheric mercury in tropical South America as inferred by a continuous total gaseous mercury record at Chacaltaya station (5240 m) in Bolivia”). A second article about atmospheric mercury at Chacaltaya, this time focused on the impact of the 2015-2016 El Niño, is nearly ready to be submitted to a journal.
I also had time to advance in the Maïdo dataset, which appears to be very “rich”: alongside continuously sampled atmospheric mercury (Hg0), other trace gases (such as ozone and SO2) as well as volatile organic compounds were also measured at Maïdo. One striking feature appearing in Maïdo Hg0 observations is that diel cycles are very regular, with higher Hg0 during daytime and significantly lower Hg0 during nighttime. I hope to be able to extract information about mercury dynamics in the tropical Indian Ocean by looking more closely at these diel cycles and by considering the behavior of auxiliary variables. While the data treatment of this dataset is still in the early stages, the first results were already presented at the Goldschmidt2021 conference.
Even though most of my work involves reading articles, discussing with colleagues, or coding on my computer, I also had the opportunity of a more hands-on experience involving mercury: During a secondment to the GET in Toulouse, I got to work in the chemical analysis of oxidized mercury samples.
By Alkuin Koenig (ESR 1)