Anthropogenic mercury signals in lake sediments from southernmost Patagonia, Chile

Natural and anthropogenic impacts on mercury accumulation in Xiaohai Lagoon, South China over the last 1200 years

Anthropogenic use and release of mercury (Hg) have profoundly affected the global Hg cycle since preindustrial times. However, it is often difficult to quantify the relative contributions of natural and anthropogenic factors to environmental Hg accumulation. Here, we have presented a 1200-year record of Hg deposition in a sediment core from the Xiaohai Lagoon (South China), in combination with multiple environmental indicators (e.g., geochemical elements, grain size and total organic carbon, etc.). Using principal component analysis (PCA) and stepwise regression analysis (SRA), we aimed to explore the latent processes governing the accumulation of Hg over time and to quantitatively assess the natural and anthropogenic impacts on Hg deposition over the last millennium in Xiaohai Lagoon. Our results have demonstrated that between ∼ 870 and ∼ 1860 CE, natural factors were the main drivers controlling Hg concentrations in the lagoon. These were directly driven by higher soil erosion and increased inputs of fine-grained matter. However, from 1860 to 2013 CE, enhanced anthropogenic activities played a significant role in Hg accumulation in Xiaohai Lagoon. Anthropogenic Hg fluxes increased significantly from ∼ 1860 CE, peaked several times during the 1860s to the 1950s, accelerated from the late 1950s to the early 2000s, and then declined gradually owing to the stringent environmental protection strategies and efficient pollutant control technologies. Our results have suggested that the increased anthropogenic Hg inputs between the 1860s and mid-1970s were mostly attributed to wars, the "Westernization Movement", and global industrial activity, with a surge mainly after the 1980s dominated by industrial activities in China and numerous developing countries in Southeast Asia. This study has shown the natural and anthropogenic influences associated with mercury pollution through quantitative analysis and can deepen our understanding of the processes and mechanisms of mercury deposition in natural environments under the influence of human activities.

A 2200-year record of Andean Condor diet and nest site usage reflects natural and anthropogenic stressors

Understanding how animals respond to large-scale environmental changes is difficult to achieve because monitoring data are rarely available for more than the past few decades, if at all. Here, we demonstrate how a variety of palaeoecological proxies (e.g. isotopes, geochemistry and DNA) from an Andean Condor (Vultur gryphus) guano deposit from Argentina can be used to explore breeding site fidelity and the impacts of environmental changes on avian behaviour. We found that condors used the nesting site since at least approximately 2200 years ago, with an approximately 1000-year nesting frequency slowdown from ca 1650 to 650 years before the present (yr BP). We provide evidence that the nesting slowdown coincided with a period of increased volcanic activity in the nearby Southern Volcanic Zone, which resulted in decreased availability of carrion and deterred scavenging birds. After returning to the nest site ca 650 yr BP, condor diet shifted from the carrion of native species and beached marine animals to the carrion of livestock (e.g. sheep and cattle) and exotic herbivores (e.g. red deer and European hare) introduced by European settlers. Currently, Andean Condors have elevated lead concentrations in their guano compared to the past, which is associated with human persecution linked to the shift in diet.

Two cetacean species reveal different long-term trends for toxic trace elements in European Atlantic French waters

Cetaceans have been naturally exposed to toxic trace elements (TEs) on an evolutionary time scale. Hence, they have developed mechanisms to control and/or mitigate their toxic effects. These long-lived species located at high trophic positions and bioaccumulating toxic elements are assumed to be good biomonitoring organisms. However, anthropogenic emissions have strongly increased environmental levels of toxic TEs in the last decades, questioning the efficiency of the detoxication mechanisms in cetaceans. In this context, temporal trends of mercury (Hg), cadmium (Cd) and lead (Pb) concentrations were studied through the analysis of 264 individuals from two cetacean species the common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) and belonging to two different Management Units (MUs) for the latter. These individuals stranded along the French Atlantic coasts from 2000s to 2017. All the trends presented were age- and sex-corrected and stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were measured as proxies of their feeding ecology. Results showed that Pb concentrations clearly decreased over time in both species and MUs. This decrease agrees with the lead petrol regulation after 2000s, supporting the use of these species as valuable bioindicators of changes for TE levels in the marine environment. A significant long-term increase of total Hg concentrations was only observed in common dolphins. Cadmium concentrations also revealed different trends over the period in both species. The different Hg and Cd trends observed in the two species, probably reflected a contrasted contamination of habitat and prey species than a global increase of the contamination in the environment. These results highlight the necessity and gain of using different species to monitor changes in marine environments, each of them informing on the contamination of its own ecological niche. Lastly, the Se:Hg molar ratios of species suggested a low risk for Hg toxicity over time.

250-year records of mercury and trace element deposition in two lakes from Cajas National Park, SW Ecuadorian Andes

Historical records of trace elements in lake sediments provide source-to-sink information about potentially toxic pollutants across space and time. We investigated two lakes located at different elevations in the Ecuadorian Andes to understand how trace element fluxes are related to (i) geology, (ii) erosion in the watersheds, and (iii) local point sources and atmospheric loads. In remote Lake Fondococha (4150 m a.s.l.), total Hg fluxes stay constant between ca. 1760 and 1950 and show an approximately 4.4-fold increase between pre-1950 and post-1950 values. The post-1950 increase in fluxes of other trace elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb) is lower (2.1-3.0-fold) than for Hg. Mostly lithogenic sources and enhanced soil erosion contribute to their post-1950 increase (lithogenic contribution: > 85%, Hg: ~ 58%). Average post-1950 Hg fluxes are approximately 4.3 times higher in peri-urban Lake Llaviucu (3150 m a.s.l.) than in the remote Lake Fondococha. Post-1950 fluxes of the other trace elements showed larger differences between Lakes Fondococha and Llaviucu (5.2 < 25-29.5-fold increase; Ni < Pb-Cd). The comparison of the post-1950 average trace element fluxes that are derived from point and airborne sources revealed 5-687 (Hg-Pb) times higher values in Lake Llaviucu than in Lake Fondococha suggesting that Lake Llaviucu's proximity to the city of Cuenca strongly influences its deposition record (industrial emissions, traffic, caged fishery). Both lakes responded with temporary drops in trace element accumulations to park regulations in the 1970s and 1990s, but show again increasing trends in recent times, most likely caused by increase in vehicular traffic and openings of copper and gold mines around Cajas National Park.

Structural equation modeling of long-term controls on mercury and bromine accumulation in Pinheiro mire (Minas Gerais, Brazil)

The application of statistical modeling is still infrequent in mercury research in peat, despite the ongoing debate on the weight of the diverse factors (climate, peat decomposition, vegetation changes, etc.) that may affect mercury accumulation. One of the few exceptions is the Hg record of Pinheiro mire (souheast Brazil). Previous studies on this mire modeled mercury using principal components regression and partial least squares. These methods assume independence between factors, which is seldom the case in natural systems, thus hampering the identification of mediating effects and interactions. To overcome these limitations, in this reserach we use structural equation modeling (PLS-SEM) to model mercury and bromine peat records - bromine has been used in some investigations to normalize mercury accumuation. The mercury model explained 83% of the variance and suggested a complex control: increased peat decomposition, dust deposition and humid climates enhanced mercury accumulation, while increased mineral fluxes resulted in a decrease in mercury accumulation. The bromine model explained 90% of the variation in concentrations: increased dust deposition and peat decomposition promoted bromine accumulation, while time (i.e. peat age) promoted bromine depletion. Thus, although mercury and bromine are both organically bound elements with relevant atmospheric cycles the weights of the factors involved in their accumulation differed significantly. Our results suggest caution when using bromine to normalize mercury accumulation. PLS-SEM results indicate a large time dependence of peat decomposition, catchment mineral fluxes, long-term climate change, and atmospheric deposition; while atmospheric dust, mineral fluxes and peat decomposition showed high to moderate climate dependency. In particular, they also point to a relevant role of autogenic processes (i.e. the build up and expansion of the mire within the catchment), which controlled local mineral fluxes; an aspect that has seldom been considered.

Environmental archives of atmospheric Hg deposition - A review

Environmental archives offer an opportunity to reconstruct temporal trends in atmospheric Hg deposition at various timescales. Lake sediment and peat have been the most widely used archives; however, new records from ice, tree rings, and the measurement of Hg stable isotopes, are offering new insights into past Hg cycling. Preindustrial Hg deposition has been studied over decadal to millennial timescales extending as far back as the late Pleistocene. Exploitation of mercury deposits (mainly cinnabar) first began during the mid to late Holocene in South America, Europe, and Asia, but increased dramatically during the Colonial era (1532-1900) for silver production. However, evidence for preindustrial Hg pollution is restricted to regions directly downwind or downstream of cinnabar or precious metal mining centers. Excluding these areas, there has been an approximately four-fold increase in atmospheric deposition globally over the industrial era (i.e., since 1800-1850), though regional differences exist, especially during the early 20th Century. Lake sediments, peat, ice, and tree rings are all influenced by (and integrate) a range of processes. For example, lake sediments are influenced by atmospheric deposition, sediment focusing, and the input of allochthonous material from the watershed, peat records reflect atmospheric deposition and biotic uptake, ice cores are a record of Hg scrubbed during precipitation, and tree rings record atmospheric concentrations. No archive represents an absolute record of past Hg deposition or concentrations, and post-depositional transformation of Hg profiles remains an important topic of research. However, natural archives continue to provide important insight into atmospheric Hg cycling over various timescales.

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

Deglaciation has accelerated the transport of minerals as well as modern and ancient organic matter from land to fjord sediments in Spitsbergen, Svalbard, in the European Arctic Ocean. Consequently, such sediments may contain significant levels of total mercury (THg) bound to terrestrial organic matter. The present study compared THg contents in surface sediments from three fjord settings in Spitsbergen: Hornsund in the southern Spitsbergen, which has high annual volume of loss glacier and receives sediment from multiple tidewater glaciers, Dicksonfjorden in the central Spitsbergen, which receives sediment from glacifluvial rivers, and Wijdefjorden in the northern Spitsbergen, which receive sediments from a mixture of tidewater glaciers and glacifluvial rivers. Our results showed that the THg (52 ± 15 ng g^-1) bound to organic matter (OM) was the highest in the Hornsund surface sediments, where the glacier loss (0.44 km³ yr^-1) and organic carbon accumulation rates (9.3 ~ 49.4 g m^-2 yr^-1) were elevated compared to other fjords. Furthermore, the δ¹³C (-27 ~ -24‰) and δ³⁴S values (-10 ~ 15‰) of OM indicated that most of OM were originated from terrestrial sources. Thus, the temperature-driven glacial melting could release more OM originating from the meltwater or terrestrial materials, which are available for THg binding in the European Arctic fjord ecosystems.

Atmospheric mercury accumulation rate in northeastern China during the past 800 years as recorded by the sediments of Tianchi Crater Lake

An evaluation of the history of anthropogenic mercury (Hg) emissions is needed to quantify total atmospheric Hg emissions since the Industrial Revolution. Thus more long-term records of Hg accumulation rate from natural archives are needed. In the present study, a sediment core from Tianchi Lake, a crater lake in northeastern China, was used to reconstruct atmospheric Hg accumulation rates during the past 800 years. The results show that both Hg concentration and Hg accumulation rate began to increase from 29.5 to 40.2 ng g^-1 and from 1.44 to 2.26 μg m^-2 yr^-1, respectively, at ~ 1750 AD, synchronous with the initiation of the Industrial Revolution. The Hg accumulation rate and Hg concentration increased significantly at ~ 1850 AD, and subsequently, there were two prominent peaks, at ~ 1940 AD and ~ 1980 AD, which are temporally consistent with the Second World War and the peak in commercial usage of Hg, respectively. The Hg accumulation rate and Hg concentration decreased after ~ 1980 AD, possibly because of the decrease in the global Hg background at that time. Differences in regional Hg emissions and atmospheric circulation may be responsible for the different trends in Hg accumulation rate after ~ 1980 AD in the Tibetan Plateau and northeastern China. Our results provide new data for evaluating natural and anthropogenic Hg emissions to the atmosphere in China.

Increase in anthropogenic mercury in marginal sea sediments of the Northwest Pacific Ocean

Over the past century, the addition of anthropogenic mercury (Hg^ANTH) to vast areas of North Pacific marginal seas adjacent to the northeast Asian continent has tripled. Analysis of sediment cores showed that the rate of Hg^ANTH addition (Hg^ANTH flux) was greatest in the East China and Yellow Seas (9.1 μg m^-2 yr^-1) in the vicinity of China (the source continent), but was small in the Bering and western Arctic Ocean (Chukchi Sea) (0.9 μg m^-2 yr^-1; the regions furthest from China). Our results show that Hg^ANTH has reached open ocean sedimentary environments over extended areas of the northwestern Pacific Ocean, via the formation of organic-mercury complexes and deposition. The implication of these findings is that the addition of Hg^ANTH (via atmospheric deposition and riverine input) to the ocean environment is responsible for elevated Hg flux into sedimentary environments in the northwest Pacific Ocean.

Assessing the impact of long-term changes in climate and atmospheric deposition on a shallow alpine lake from southeast Tibet

Regional warming and atmospheric nitrogen deposition have been widely recorded to impact remote catchments and alpine lakes; however, their independent roles and interactions have rarely been identified. Here, we combined down-core analyses of sedimentary mercury (Hg) and aluminum (Al) with multiple proxies (i.e. nitrogen stable isotope, chlorophyll a pigments, diatoms) for a radiometrically-dated sediment core of an alpine lake in southeast Tibet to track the atmospheric deposition of pollutants, and to examine possible effects of climate and catchment forcing over the past three centuries. The sediment data revealed that airborne deposition of Hg was recorded from the ~1860s, with an accelerating increase in anthropogenic Hg flux since the ~1960s. A synchronous decrease in reconstructed lake-water TOC indicated that acid deposition may have affected lake-water carbon concentrations and impaired catchment export of decomposed organic matter (OM). A moderate depletion of bulk sediment δ¹⁵N started from the ~1820s, but was followed by an enriching trend after the ~1970s. This positive shift of δ¹⁵N was associated with elevated sediment OM and decreased catchment runoff of clastic materials (as inferred by Al). Sediment OM content displayed an accelerating increase from the ~1960s, with an increased input of autochthonous sources (i.e. lower bulk sediment C:N ratios), such as algae (as inferred by sedimentary chlorophyll a pigments). Meanwhile, climate warming and decreased lake-water TOC enhanced the production of algae, which was characterized by a more enriched δ¹⁵N signal than that of allochthonous OM. Furthermore, atmospheric acid deposition was significantly related to diatom assemblage changes, with an increase in acidophilous taxa. Our sediment evidence revealed the dominating impact of climate and catchment processes on lake-water chemistry and algal shifts in the context of atmospheric nitrogen deposition, and highlighted an increasing link of external forcing with in-lake processes in enriching sediment δ¹⁵N signal over the last few decades.

The Role of Climate: 71 ka of Atmospheric Mercury Deposition in the Southern Hemisphere Recorded by Rano Aroi Mire, Easter Island (Chile)

The study of mercury accumulation in peat cores provides an excellent opportunity to improve the knowledge on mercury cycling and depositional processes at remote locations far from pollution sources. We analyzed mercury concentrations in 150 peat samples from two cores from Rano Aroi (Easter Island, 27° S) and in selected vegetation samples of present-day flora of the island, in order to characterize the mercury cycling for the last ~71 ka BP. The mercury concentrations showed values ranging between 35 and 200 ng g−1, except for a large maxima (~1000 ng g−1) which occurred at the end of the Last Glacial Maximum (LGM, ~20 ka cal BP) in both peat cores. Low temperatures during the LGM would accelerate the atmospheric oxidation of Hg(0) to divalent mercury that, coupled with higher rainfall during this period, most likely resulted in a very efficient surface deposition of atmospheric mercury. Two exceptional short-lived Hg peaks occurred during the Holocene at 8.5 (350 ng g−1) and 4.7 (1000 ng g−1) ka cal BP. These values are higher than those recorded in most peat records belonging to the industrial period, highlighting that natural factors played a significant role in Hg accumulation—sometimes even more so than anthropogenic sources. Our results suggest that wet deposition, linked to atmospheric oxidation, was the main process controlling the short-lived Hg events, both in the mire and in the catchment soils.

Prediction of Holocene Mercury Accumulation Trends by Combining Palynological and Geochemical Records of Lake Sediments (Black Forest, Germany)

Forest vegetation plays a key role in the cycling of mercury (Hg) and organic matter (OM) in terrestrial ecosystems. Litterfall has been indicated as the major transport vector of atmospheric Hg to forest soils, which is eventually transported and stored in the sediments of forest lakes. Hence, it is important to understand how changes in forest vegetation affect Hg in soil and its biogeochemical cycling in lake systems. We investigated the pollen records and the geochemical compositions of sediments from two lakes (Schurmsee and Glaswaldsee) in the Black Forest (Germany) to evaluate whether long-term shifts in forest vegetation induced by climate or land use influenced Hg accumulation in the lakes. We were particularly interested to determine whether coniferous forests were associated with a larger export of Hg to aquatic systems than deciduous forests. Principal components analysis followed by principal component regression enabled us to describe the evolution of the weight of the latent processes determining the accumulation of Hg over time. Our results emphasize that the in-lake uptake of Hg during warm climate periods, soil erosion after deforestation and emissions from mining and other human activities triggered changes in Hg accumulation during the Holocene stronger than the changes caused by forest vegetation alone.

Climate, Fire, and Vegetation Mediate Mercury Delivery to Midlatitude Lakes over the Holocene

The rise in mercury concentrations in lake sediment deposited over the last ∼150 years is widely recognized to have resulted from human activity. However, few studies in the Great Lakes region have used lake sediment to reconstruct atmospheric mercury deposition on millennial time scales. Here we present a 9000-year mercury record from sediment in Copper Falls; a small closed-basin lake on the Keweenaw Peninsula. Prior to abrupt increases in the 19^th and 20^th centuries, mercury remains at relatively low concentrations for the last 9000 years. Higher mercury fluxes in the early Holocene (3.4 ± 1.1 μg m^-2 yr^-1) are attributed to drier conditions and greater forest fire occurrence. The gradual decline in mercury flux over the middle to late Holocene (1.9 ± 0.2 μg m^-2 yr^-1) is interpreted to reflect a transition to wetter conditions, which reduced forest fires, and promoted the development of soil organic matter and deciduous forests that sequestered natural sources of mercury. The Copper Falls Lake record highlights the sensitivity of watersheds to changes in mercury inputs from both human and natural forcings, and provides millennial-scale context for recent mercury contamination that will aid in establishing baseline values for restoration efforts.

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 K_d 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.

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

We review recent progress in our understanding of the global cycling of mercury (Hg), including best estimates of Hg concentrations and pool sizes in major environmental compartments and exchange processes within and between these reservoirs. Recent advances include the availability of new global datasets covering areas of the world where environmental Hg data were previously lacking; integration of these data into global and regional models is continually improving estimates of global Hg cycling. New analytical techniques, such as Hg stable isotope characterization, provide novel constraints of sources and transformation processes. The major global Hg reservoirs that are, and continue to be, affected by anthropogenic activities include the atmosphere (4.4-5.3 Gt), terrestrial environments (particularly soils: 250-1000 Gg), and aquatic ecosystems (e.g., oceans: 270-450 Gg). Declines in anthropogenic Hg emissions between 1990 and 2010 have led to declines in atmospheric Hg0 concentrations and HgII wet deposition in Europe and the US (- 1.5 to - 2.2% per year). Smaller atmospheric Hg0 declines (- 0.2% per year) have been reported in high northern latitudes, but not in the southern hemisphere, while increasing atmospheric Hg loads are still reported in East Asia. New observations and updated models now suggest high concentrations of oxidized HgII in the tropical and subtropical free troposphere where deep convection can scavenge these HgII reservoirs. As a result, up to 50% of total global wet HgII deposition has been predicted to occur to tropical oceans. Ocean Hg0 evasion is a large source of present-day atmospheric Hg (approximately 2900 Mg/year; range 1900-4200 Mg/year). Enhanced seawater Hg0 levels suggest enhanced Hg0 ocean evasion in the intertropical convergence zone, which may be linked to high HgII deposition. Estimates of gaseous Hg0 emissions to the atmosphere over land, long considered a critical Hg source, have been revised downward, and most terrestrial environments now are considered net sinks of atmospheric Hg due to substantial Hg uptake by plants. Litterfall deposition by plants is now estimated at 1020-1230 Mg/year globally. Stable isotope analysis and direct flux measurements provide evidence that in many ecosystems Hg0 deposition via plant inputs dominates, accounting for 57-94% of Hg in soils. Of global aquatic Hg releases, around 50% are estimated to occur in China and India, where Hg drains into the West Pacific and North Indian Oceans. A first inventory of global freshwater Hg suggests that inland freshwater Hg releases may be dominated by artisanal and small-scale gold mining (ASGM; approximately 880 Mg/year), industrial and wastewater releases (220 Mg/year), and terrestrial mobilization (170-300 Mg/year). For pelagic ocean regions, the dominant source of Hg is atmospheric deposition; an exception is the Arctic Ocean, where riverine and coastal erosion is likely the dominant source. Ocean water Hg concentrations in the North Atlantic appear to have declined during the last several decades but have increased since the mid-1980s in the Pacific due to enhanced atmospheric deposition from the Asian continent. Finally, we provide examples of ongoing and anticipated changes in Hg cycling due to emission, climate, and land use changes. It is anticipated that future emissions changes will be strongly dependent on ASGM, as well as energy use scenarios and technology requirements implemented under the Minamata Convention. We predict that land use and climate change impacts on Hg cycling will be large and inherently linked to changes in ecosystem function and global atmospheric and ocean circulations. Our ability to predict multiple and simultaneous changes in future Hg global cycling and human exposure is rapidly developing but requires further enhancement.

Historical anthropogenic mercury in two lakes of Central Chile: comparison between an urban and rural lake

Mercury concentrations in the environment tend to decrease in recent years due to environmental restrictions. Lakes store mercury in their sediments, making them potential secondary contamination sources. In South America, the occurrence of mercury in lake systems has been associated mainly with volcanic emissions and only few records anthropogenic contamination in the pre-Hispanic period. The objective of this research was to study historical anthropogenic mercury concentration in two lakes in Central Chile (La Señoraza and Pillo), in order to establish background mercury levels and their variations from preindustrial to modern periods. Different background levels and mercury concentrations were found in each lake, with significantly higher concentrations in Lake La Señoraza during the last 150 years. Mining-related activities during the nineteenth century could have a negligible influence on mercury concentrations. Later on, the use of coal railroads and subsequent employment of mercury in the cellulose industry were associated with three- and fourfold increases in mercury concentration over the nineteenth century background levels, which decrease once these activities ceased. However, in the case of Lake Pillo, an important increase in mercury concentration can be observed between 1990 and the early twenty-first century, which could be related to a higher watershed/lake area ratio, extensive agriculture, and volcanic emission, being the latter that could have contributed with mercury to both systems. Nevertheless, sedimentological characteristics in Lake Pillo can be favorable to retain mercury in this aquatic system up to the present day.

-Genomic data mining of the marine actinobacteria Streptomyces sp. H-KF8 unveils insights into multi-stress related genes and metabolic pathways involved in antimicrobial synthesis

Streptomyces sp. H-KF8 is an actinobacterial strain isolated from marine sediments of a Chilean Patagonian fjord. Morphological characterization together with antibacterial activity was assessed in various culture media, revealing a carbon-source dependent activity mainly against Gram-positive bacteria (S. aureus and L. monocytogenes). Genome mining of this antibacterial-producing bacterium revealed the presence of 26 biosynthetic gene clusters (BGCs) for secondary metabolites, where among them, 81% have low similarities with known BGCs. In addition, a genomic search in Streptomyces sp. H-KF8 unveiled the presence of a wide variety of genetic determinants related to heavy metal resistance (49 genes), oxidative stress (69 genes) and antibiotic resistance (97 genes). This study revealed that the marine-derived Streptomyces sp. H-KF8 bacterium has the capability to tolerate a diverse set of heavy metals such as copper, cobalt, mercury, chromate and nickel; as well as the highly toxic tellurite, a feature first time described for Streptomyces. In addition, Streptomyces sp. H-KF8 possesses a major resistance towards oxidative stress, in comparison to the soil reference strain Streptomyces violaceoruber A3(2). Moreover, Streptomyces sp. H-KF8 showed resistance to 88% of the antibiotics tested, indicating overall, a strong response to several abiotic stressors. The combination of these biological traits confirms the metabolic versatility of Streptomyces sp. H-KF8, a genetically well-prepared microorganism with the ability to confront the dynamics of the fjord-unique marine environment.

Mercury pollution in the lake sediments and catchment soils of anthropogenically-disturbed sites across England

Sediment cores and soil samples were taken from nine lakes and their catchments across England with varying degrees of direct human disturbance. Mercury (Hg) analysis demonstrated a range of impacts, many from local sources, resulting from differing historical and contemporary site usage and management. Lakes located in industrially important areas showed clear evidence for early Hg pollution with concentrations in sediments reaching 400-1600 ng g^-1 prior to the mid-19th century. Control of inputs resulting from local management practices and a greater than 90% reduction in UK Hg emissions since 1970 were reflected by reduced Hg pollution in some lakes. However, having been a sink for Hg deposition for centuries, polluted catchment soils are now the major Hg source for most lakes and consequently recovery from reduced Hg deposition is being delayed.

Is mercury from small-scale gold mining prevalent in the southeastern Peruvian Amazon?

There is an ongoing debate on the fate of mercury (Hg) in areas affected by artisanal and small-scale gold mining (ASGM). Over the last 30 years, ASGM has released 69 tons of Hg into the southeastern Peruvian Amazon. To investigate the role of suspended matter and hydrological factors on the fate of ASGM-Hg, we analysed riverbank sediments and suspended matter along the partially ASGM-affected Malinowski-Tambopata river system and examined Hg accumulation in fish. In addition, local impacts of atmospheric Hg emissions on aquatic systems were assessed by analysing a sediment core from an oxbow lake. Hg concentrations in riverbank sediments are lower (20-53 ng g^-1) than in suspended matter (∼400-4000 ng g^-1) due to differences in particle size. Elevated Hg concentrations in suspended matter from ASGM-affected river sections (∼1400 vs. ∼30-120 ng L^-1 in unaffected sections) are mainly driven by the increased amount of suspended matter rather than increased Hg concentrations in the suspended matter. The oxbow lake sediment record shows low Hg concentrations (64-86 ng g^-1) without evidence of any ASGM-related increase in atmospheric Hg input. Hg flux variations are mostly an effect of variations in sediment accumulation rates. Moreover, only 5% of the analysed fish (only piscivores) exceed WHO recommendations for human consumption (500 ng g^-1). Our findings show that ASGM-affected river sections in the Malinowski-Tambopata system do not exhibit increased Hg accumulation, indicating that the released Hg is either retained at the spill site or transported to areas farther away from the ASGM areas. We suspect that the fate of ASGM-Hg in such tropical rivers is mainly linked to transport associated with the suspended matter, especially during high water situations. We assume that our findings are typical for ASGM-affected areas in tropical regions and could explain why aquatic systems in such ASGM regions often show comparatively modest enrichment in Hg levels.

Penguins as bioindicators of mercury contamination in the southern Indian Ocean: geographical and temporal trends

Penguins have been recently identified as useful bioindicators of mercury (Hg) transfer to food webs in the Southern Ocean over different spatial and temporal scales. Here, feather Hg concentrations were measured in adults and chicks of all the seven penguin species breeding in the southern Indian Ocean, over a large latitudinal gradient spanning Antarctic, subantarctic and subtropical sites. Hg was also measured in feathers of museum specimens of penguins collected at the same sites in the 1950s and 1970s. Our aim was to evaluate geographical and historical variations in Hg transfer to penguins, while accounting for feeding habits by using the stable isotope technique (δ(13)C, habitat; δ(15)N, diet/trophic level). Adult feather Hg concentrations in contemporary individuals ranged from 0.7 ± 0.2 to 5.9 ± 1.9 μg g(-1) dw in Adélie and gentoo penguins, respectively. Inter-specific differences in Hg accumulation were strong among both adults and chicks, and mainly linked to feeding habits. Overall, penguin species that feed in Antarctic waters had lower feather Hg concentrations than those that feed in subantarctic and subtropical waters, irrespective of age class and dietary group, suggesting different Hg incorporation into food webs depending on the water mass. While accounting for feeding habits, we detected different temporal variations in feather Hg concentrations depending on species. Notably, the subantarctic gentoo and macaroni penguins had higher Hg burdens in the contemporary rather than in the historical sample, despite similar or lower trophic levels, respectively. Whereas increases in Hg deposition have been recently documented in the Southern Hemisphere, future monitoring is highly needed to confirm or not this temporal trend in penguins, especially in the context of actual changing Hg emission patterns and global warming.

Historical records of mercury in southern latitudes over 1600 years: Lake Futalaufquen, Northern Patagonia

Mercury is released to the environment from natural and anthropogenic sources, and through atmospheric transport is distributed globally. Lake Futalaufquen (42.8°S) is an oligotrophic lake located in Los Alerces National Park (Northern Patagonia), providing a remote and unpolluted study system. A lacustrine sedimentary sequence revealed 1600 years of Hg deposition, identifying natural baselines and marked peaks not correlated with long-range atmospheric transport. Organic matter and catchment erosion were discarded as Hg drivers. Natural background, pre-1300 CE Hg concentrations, ranged between 27 and 47 ng g(-1) (accumulation rates from 8 to 15μg m(-2) y(-1)). From 1300 CE on, the Hg background profile did not follow the generally increasing Hg pattern observed in both Southern and Northern Hemisphere since pre-industrial times. It was not until the last century that a 1.6-fold increase is observed in the Hg accumulation rate, considered among the lowest increments in southern South America. Noteworthy local/regional sources of Hg for this area, along with global transport, are forest fires and volcanic activity. Between approx. 1340 and 1510 CE, sharp increase in Hg concentration and accumulation rate (up to 204 ng g(-1) and 51 μg m(-2) y(-1), respectively) were clearly associated with extended fire episodes. Furthermore, high Hg peaks during the last 300 years were associated with volcanic eruptions in northernmost Patagonia together with fairly irregular fire episodes, caused by anthropogenic burning by settling population in the Andes.

Spatial variation, fractionation and sedimentary records of mercury in the East China Sea

Surface and core sediments were collected to study distributions, phases and potential environmental risk of Hg and to reconstruct anthropogenic Hg change over the past one hundred years in the East China Sea (ECS). Hg contents in surface sediments displayed a decreasing gradient from the Changjiang Estuary to the outer sea. Sequential extraction analysis showed that Hg mainly existed as residual fraction (70.18% of total), and while organic matter fraction (22.96% of total) was the main component of labile fraction, indicating the strong adsorption of organic matters on Hg. Enrichment factor and sediment quality guidelines suggested that Hg in sediments of ECS were at minor enrichment and low adverse effect. Temporal distributions of total Hg content, labile fraction, burial flux and anthropogenic Hg flux showed that anthropogenic Hg input increased since the 1960s, which was related to riverine input and atmospheric transport.

Use of the mercury record in Red Tarn sediments to reveal air pollution history and the implications of catchment erosion

Red Tarn is a cirque lake with a small ratio of terrestrial area to lake area, surrounded by glacial edges with little soil in the catchment. A sediment core taken from the deepest area of the lake was (210)Pb dated and validated by (137)Cs and (241)Am stratigraphic records. The core was analysed for mercury (Hg) and other elements. The results show Hg pollution before the mid-19th century, and thereafter, a rapid increase in Hg pollution into modern time, followed by a decline in pollution since 1968-1970. This agrees well with the decline in UK Hg emissions since the Clear Air Act of 1968. The results suggest that the core has recorded Hg air pollution history, and it can be used to benchmark Hg changes in the sediments from other lakes in the region up to the late 1980s. However, increased (210)Pb fluxes after the late 1980s indicate enhanced catchment erosion, which has brought more legacy Hg in the catchment into the lake. As a consequence, since 2000, the Hg in the sediment record no longer reflects the atmospheric Hg deposition. The core shows how dominant Hg sources for the lake changed from atmospheric deposition to the catchment inputs, and demonstrates that contaminated catchment inputs have not only increased Hg fluxes to the lake sediments but have also increased Hg concentrations in the sediments.

Public Health Perspectives on Aquaculture

Nearly half of all seafood consumed globally comes from aquaculture, a method of food production that has expanded rapidly in recent years. Increasing seafood consumption has been proposed as part of a strategy to combat the current non-communicable disease (NCD) pandemic, but public health, environmental, social, and production challenges related to certain types of aquaculture production must be addressed. Resolving these complicated human health and ecologic trade-offs requires systems thinking and collaboration across many fields; the One Health concept is an integrative approach that brings veterinary and human health experts together to combat zoonotic disease. We propose applying and expanding the One Health approach to facilitate collaboration among stakeholders focused on increasing consumption of seafood and expanding aquaculture production, using methods that minimize risks to public health, animal health, and ecology. This expanded application of One Health may also have relevance to other complex systems with similar trade-offs.

Atmospheric Hg emissions from preindustrial gold and silver extraction in the Americas: a reevaluation from lake-sediment archives

Human activities over the last several centuries have transferred vast quantities of mercury (Hg) from deep geologic stores to actively cycling earth-surface reservoirs, increasing atmospheric Hg deposition worldwide. Understanding the magnitude and fate of these releases is critical to predicting how rates of atmospheric Hg deposition will respond to future emission reductions. The most recently compiled global inventories of integrated (all-time) anthropogenic Hg releases are dominated by atmospheric emissions from preindustrial gold/silver mining in the Americas. However, the geophysical evidence for such large early emissions is equivocal, because most reconstructions of past Hg-deposition have been based on lake-sediment records that cover only the industrial period (1850-present). Here we evaluate historical changes in atmospheric Hg deposition over the last millennium from a suite of lake-sediment cores collected from remote regions of the globe. Along with recent measurements of Hg in the deep ocean, these archives indicate that atmospheric Hg emissions from early mining were modest as compared to more recent industrial-era emissions. Although large quantities of Hg were used to extract New World gold and silver beginning in the 16th century, a reevaluation of historical metallurgical methods indicates that most of the Hg employed was not volatilized, but rather was immobilized in mining waste.

Effects of historical and modern mining on mercury deposition in southeastern Peru

Both modern anthropogenic emissions of mercury (Hg), primarily from artisanal and small-scale gold mining (ASGM), and preindustrial anthropogenic emissions from mining are thought to have a large impact on present-day atmospheric Hg deposition. We study the spatial distribution of Hg and its depositional history over the past ∼400 years in sediment cores from lakes located regionally proximal (∼90-150 km) to the largest ASGM in Peru and distal (>400 km) to major preindustrial mining centers. Total Hg concentrations in surface sediments from fourteen lakes are typical of remote regions (10-115 ng g(-1)). Hg fluxes in cores from four lakes demonstrate preindustrial Hg deposition in southeastern Peru was spatially variable and at least an order of magnitude lower than previously reported fluxes in lakes located closer to mining centers. Average modern (A.D. 2000-2011) Hg fluxes in these cores are 3.4-6.9 μg m(-2) a(-1), compared to average preindustrial (A.D. 1800-1850) fluxes of 0.8-2.5 μg m(-2) a(-1). Modern Hg fluxes determined from the four lakes are on average 3.3 (±1.5) times greater than their preindustrial fluxes, similar to those determined in other remote lakes around the world. This agreement suggests that Hg emissions from ASGM are likely not significantly deposited in nearby down-wind regions.