Enhanced mercury reduction in the South Atlantic Ocean during carbon remineralization

Highlights • Dissolved gaseous mercury can be calculated from modeled dissolved inorganic carbon. • Modeled dissolved gaseous mercury agrees well with worldwide observations. • Dissolved gaseous mercury is related to depth and macronutrients concentrations. Mercury (Hg) in seawater is subject to interconversions via (photo)chemical and (micro)biological processes that determine the extent of dissolved gaseous mercury (DGM) (re)emission and the production of monomethylmercury. We investigated Hg speciation in the South Atlantic Ocean on a GEOTRACES cruise along a 40°S section between December 2011 and January 2012 (354 samples collected at 24 stations from surface to 5250 m maximum depth). Using statistical analysis, concentrations of methylated mercury (MeHg, geometric mean 35.4 fmol L−1) were related to seawater temperature, salinity, and fluorescence. DGM concentrations (geometric mean 0.17 pmol L−1) were related to water column depth, concentrations of macronutrients and dissolved inorganic carbon (DIC). The first-ever observed linear correlation between DGM and DIC obtained from high-resolution data indicates possible DGM production by organic matter remineralization via biological or dark abiotic reactions. DGM concentrations projected from literature DIC data using the newly discovered DGM–DIC relationship agreed with published DGM observations

Biogeochemical, isotopic and bacterial distributions trace oceanic abyssal circulation

We explore the possibility of tracing routes of dense waters toward and within the ocean abyss by the use of an extended set of observed physical and biochemical parameters. To this purpose, we employ mercury, isotopic oxygen, biopolymeric carbon and its constituents, together with indicators of microbial activity and bacterial diversity found in bottom waters of the Eastern Mediterranean. In this basin, which has been considered as a miniature global ocean, two competing sources of bottom water (one in the Adriatic and one in the Aegean seas) contribute to the ventilation of the local abyss. However, due to a recent substantial reduction of the differences in the physical characteristics of these two water masses it has become increasingly complex a water classification using the traditional approach with temperature, salinity and dissolved oxygen alone. Here, we show that an extended set of observed physical and biochemical parameters allows recognizing the existence of two different abyssal routes from the Adriatic source and one abyssal route from the Aegean source despite temperature and salinity of such two competing sources of abyssal water being virtually indistinguishable. Moreover, as the near-bottom development of exogenous bacterial communities transported by convectively-generated water masses in the abyss can provide a persistent trace of episodic events, intermittent flows like those generating abyssal waters in the Eastern Mediterranean basin may become detectable beyond the availability of concomitant measurements.We explore the possibility of tracing routes of dense waters toward and within the ocean abyss by the use of an extended set of observed physical and biochemical parameters. To this purpose, we employ mercury, isotopic oxygen, biopolymeric carbon and its constituents, together with indicators of microbial activity and bacterial diversity found in bottom waters of the Eastern Mediterranean. In this basin, which has been considered as a miniature global ocean, two competing sources of bottom water (one in the Adriatic and one in the Aegean seas) contribute to the ventilation of the local abyss. However, due to a recent substantial reduction of the differences in the physical characteristics of these two water masses it has become increasingly complex a water classification using the traditional approach with temperature, salinity and dissolved oxygen alone. Here, we show that an extended set of observed physical and biochemical parameters allows recognizing the existence of two different abyssal routes from the Adriatic source and one abyssal route from the Aegean source despite temperature and salinity of such two competing sources of abyssal water being virtually indistinguishable. Moreover, as the near-bottom development of exogenous bacterial communities transported by convectively-generated water masses in the abyss can provide a persistent trace of episodic events, intermittent flows like those generating abyssal waters in the Eastern Mediterranean basin may become detectable beyond the availability of concomitant measurements. © 2016 Rubino et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Mercury Degassing on Africa-Adriatic Tectonic Plate Margin

Beside anthropogenic influences, mercury in the environment can also be of natural origin. Among geologic sources, volcanic activity has been of main interest so far. Modern estimations of global natural emissions are between 2000 and 5200 tonnes per year. However, these estimates are very uncertain, thus more detailed and systematic research on natural sources of mercury is necessary. Tectonic activity is connected to certain phenomena such as degassing of Hg and other gases from active faults, geothermal activity, volcanoes, etc., especially on tectonic plate margins. Elemental mercury concentrations in air, soil gases and fluxes, as well as its speciation, in connection to tectonic activity, were studied in different environments such are karst cave (Postojna Cave), active volcano areas (Mt. Etna, Italy), and active tectonic areas in the Mediterranean Basin on Africa-Adriatic tectonic plate margin. Postojna Cave is characterized by elevated Hg (up to 150 ng m-3) air concentrations at certain areas in vicinity of active faults; however the concentrations showed also strong seasonal variations. Mt. Etna on Sicily is the largest and most active Mediterranean volcano. Concentrations of mercury in air in the vicinity of the volcano are relatively high (between 4 and 30 ng m-3) and rise towards the summit crater (65 to 130 ng m-3). Concentrations in sulphatare and fumaroles gases on the summit of the volcano can reach very high values (even up to 60 μg m-3). The Mediterranean Basin is characterized by strong tectonic activity as a consequence of subduction of African plate under the Eurasian plate. A possible source of DGM (dissolved gaseous mercury in sea water) in deeper and bottom waters could be intensive tectonic activity of the seafloor, since higher concentrations and portions of DGM were found near the bottom at locations with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea, Ionian Sea). Distribution of different mercury species in sediment and water of the Mediterranean Sea showed that the main source of mercury is geotectonic activity and its accompanying phenomena

Heavy metals in the sediment of Sava River, Slovenia

The Sava River is the longest river in Slovenia and it has been a subject of heavy pollution in the past (Štern & Förstner 1976). In order to determine the anthropogenic contribution of selected metals (Cd, Co, Cr, Cu, Fe, Hg, Ni, Pb and Zn) to background levels,concentrations of these metals were measured in sediments at several downstream locations.An extracting procedure using 25% (v/v) acetic acid was applied for estimation of the extent of contamination with heavy metals originating from anthropogenic activities. In addition,a normalization technique was used to determine background, naturally enriched and contamination levels. Aluminum was found to be good normalizer for most of the measured elements. The results suggest that an anthropogenic contamination of certain metal is notnecessarily connected to easily extractable fraction in 25% acetic acid. As a consequence of anthropogenic activities the elevated levels of all measured elements were found near Acroni Jesenice steelworks and at some locations downflow from biggest cities

Mercury speciation in meconium and associated factors

Meconium is formed early in gestation and it is normally not excreted until after birth. Thus it may provide a longer and cumulative record of exposure to mercury (Hg). The present study aims to speciate Hg in meconium samples (N = 488) from Slovenian and Croatian new-borns prenatally exposed to low levels of methyl-Hg (MeHg) from maternal seafood intake and to Hg0 from maternal dental amalgam fillings. We had complete data of total Hg (THg) and MeHg in meconium and THg in maternal hair (MH), while THg and MeHg in maternal blood (MB) were available only for Croatian mothers. Personal data namely maternal seafood intake, age, pre-pregnancy BMI, parity, smoking, estimated gestational age at birth, sex, and birth weight were available for the majority of participants, except the number of dental amalgams which was in most cases missing for Croatian mothers. The median THg concentration in meconium was 11.1 (range: 0.41–375.2) ng/g and inorganic Hg (Hg(II)) presented 98.8% (range: 82%–100%, CV: 2%) of THg. We observed significant correlation between meconium and MH Hg levels, with the highest correlation between hair THg and meconium MeHg. Correlation analysis including MB (available only for Croatian population) showed a significant positive correlation between THg in meconium and THg in MB (Rs = 0.642). Additionally, MeHg from MB was correlated with MeHg in meconium (Rs = 0.898), while the correlation between Hg(II) in MB and meconium was positive, but not significant. Maternal seafood intake was significantly correlated with meconium MeHg (Rs = 0.498) and Hg(II) (Rs = 0.201). Multiple linear regression (performed on the Slovenian population, N = 143) confirmed a positive association between meconium MeHg and seafood intake. Furthermore, meconium Hg(II) was positively associated with the number of maternal dental amalgam fillings, but linear regression models did not confirm correlation between seafood intake and meconium Hg(II) levels. We assume that Hg0 released from maternal dental amalgam fillings and MeHg from seafood intake were both transported through the placental barrier and portioned between different foetal compartments including meconium. Weak correlation between maternal seafood intake and Hg(II) levels in meconium suggests that there is certain evidence of MeHg demethylation. However, because this correlation was not confirmed by the multiple regression, MeHg demethylation during prenatal life cannot be neither confirmed nor excluded. Further investigations at higher level of exposure are needed to confirm this observations. We can conclude that meconium is a suitable biomarker for MeHg and Hg0 exposure during pregnancy. However, comparability of the results reported in meconium in different studies is hindered by a lack of standardized sampling protocols, storage, and analysis

Species- and habitat-specific bioaccumulation of total mercury and methylmercury in the food web of a deep oligotrophic lake

Niche segregation between introduced and native fish in Lake Nahuel Huapi, a deep oligotrophic lake in Northwest Patagonia (Argentina), occurs through the consumption of different prey. Therefore, in this work we analyzed total mercury [THg] and methylmercury [MeHg] concentrations in top predator fish and in their main prey to test whether their feeding habits influence [Hg]. Results indicate that [THg] and [MeHg] varied by foraging habitat and they increased with greater percentage of benthic diet and decreased with pelagic diet in Lake Nahuel Huapi. This is consistent with the fact that the native creole perch, a mostly benthivorous feeder, which shares the highest trophic level of the food web with introduced salmonids, had higher [THg] and [MeHg] than the more pelagic feeder rainbow trout and bentho-pelagic feeder brown trout. This differential THg and MeHg bioaccumulation observed in native and introduced fish provides evidence to the hypothesis that there are two main Hg transfer pathways from the base of the food web to top predators: a pelagic pathway where Hg is transferred from water, through plankton (with Hg in inorganic species mostly), forage fish to salmonids, and a benthic pathway, as Hg is transferred from the sediments (where Hg methylation occurs mostly), through crayfish (with higher [MeHg] than plankton), to native fish, leading to one fold higher [Hg].Fil: Arcagni, Marina. Comision Nacional de Energia Atomica. Centro Atomico Bariloche. Laboratorio de Analisis Por Activación Neutronica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Juncos, Romina. Comision Nacional de Energia Atomica. Centro Atomico Bariloche. Laboratorio de Analisis Por Activación Neutronica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Rizzo, Andrea Paula. Comision Nacional de Energia Atomica. Centro Atomico Bariloche. Laboratorio de Analisis Por Activación Neutronica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Pavlin, Majda. Institute Jožef Stefan; EsloveniaFil: Fajon, Vesna. Institute Jožef Stefan; EsloveniaFil: Arribére, María Angélica. Comision Nacional de Energia Atomica. Centro Atomico Bariloche. Laboratorio de Analisis Por Activación Neutronica; ArgentinaFil: Horvat, Milena. Institute Jožef Stefan; EsloveniaFil: Ribeiro Guevara, Sergio. Comision Nacional de Energia Atomica. Centro Atomico Bariloche. Laboratorio de Analisis Por Activación Neutronica; Argentin

Mercury speciation in prenatal exposure in Slovenian and Croatian population - PHIME study

In recent years, several studies have addressed the issue of prenatal exposure to methylmercury (MeHg) ; however, few have actually analysed MeHg blood concentrations. Our study population included mothers and their new-borns from Slovenia (central region ; N = 584) and Croatia (coastal region ; N = 234). We have measurements of total Hg (THg) and MeHg in maternal hair, maternal peripheral blood, and cord blood. Cord blood Hg concentrations were low to moderate (median THg = 1.84 ng/g and MeHg = 1.69 ng/g). The proportion of THg as MeHg (%MeHg) in maternal and cord blood varied between 4% and 100% (coefficient of variation, CV = 32%) and between 8% and 100% (CV = 20%), respectively. Our data shows that variability of %MeHg was higher at lower blood THg levels. Concentrations of MeHg in maternal blood and cord blood were highly correlated (Rs = 0.943), in the case of inorganic Hg correlation was significant but weaker (Rs = 0.198). MeHg levels in maternal blood and cord blood were positively associated with seafood intake, maternal age, and negatively associated with pre-pregnancy BMI. Additionally, MeHg in maternal blood was positively associated with plasma selenium levels, and cord blood MeHg was negatively associated with parity. The results of multiple linear regression models showed that speciation analysis provides more defined estimation of prenatal exposure in association modelling. Associations between Hg exposure and cognitive performance of children (assessed using Bayley Scales of Infant and Toddler development) adjusted for maternal or child Apolipoprotein E genotypes showed higher model R2 and lower p-values when adjusted for MeHg compared to THg. This study demonstrates that Hg speciation improves the association between exposure and possible negative health effects

Mercury in a stream-lake network of Andean Patagonia (Southern Volcanic Zone): Partitioning and interaction with dissolved organic matter

Lake Nahuel Huapi (NH) is a large, ultraoligotrophic deep system located in Nahuel Huapi National Park (NHNP) and collecting a major headwater network of Northwestern Patagonia (Argentina). Brazo Rincón (BR), the westernmost branch of NH, is close to the active volcanic formation Puyehue-Cordón Caulle. In BR, aquatic biota and sediments display high levels of total Hg (THg), ranging in contamination levels although it is an unpolluted region. In this survey, Hg species and fractionation were assessed in association with dissolved organic matter (DOM) in several aquatic systems draining to BR. THg varied between 16.8 and 363 ng L−1, with inorganic Hg (Hg2+) contributing up to 99.8% and methyl mercury (MeHg) up to 2.10%. DOC levels were low (0.31–1.02 mg L−1) resulting in high THg:DOC and reflecting in high Hg2+ availability for binding particles (partitioning coefficient log Kd up to 6.03). In streams, Hg fractionation and speciation related directly with DOM terrestrial prints, indicating coupled Hg-DOM inputs from the catchment. In the lake, DOM quality and photochemical and biological processing drive Hg fractionation, speciation and vertical levels. Dissolved gaseous Hg (Hg0) reached higher values in BR (up to 3.8%), particularly in upper lake layers where solar radiation enhances the photoreduction of Hg2+ and Hg-DOM complexes. The environmental conditions in BR catchment promote Hg2+ binding to abiotic particles and bioaccumulation and the production of Hg0, features enhancing Hg mobilization among ecosystem compartments. Overall, the aquatic network studied can be considered a “natural Hg hotspot” within NHNP.Fil: Soto Cárdenas, Estela Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Dieguez, Maria del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Queimaliños, Claudia Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Rizzo, Andrea Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; ArgentinaFil: Fajon, Vesna. Jožef Stefan Institute; EsloveniaFil: Kotnik, Joze. Jožef Stefan Institute; EsloveniaFil: Horvat, Milena. Jožef Stefan Institute; EsloveniaFil: Ribeiro, Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentin