Photodegradation is critical to reduce the potent neurotoxic methylmercury (MeHg) in water and its subsequent accumulation along food chains. However, this process has been largely ignored in rice paddies, which are hotspots of MeHg production and receive about a quarter of the world's developed freshwater resources. Here, we reported that significant MeHg photodegradation, primarily mediated by hydroxyl radicals, occurs in the overlying water during rice growth.
View Article and Find Full Text PDFMethylmercury (MeHg) is the most neurotoxic and bioaccumulative form of mercury (Hg) present in the terrestrial and aquatic food sources of boreal ecosystems, posing potential risks to wildlife and human health. Harvesting impacts on Hg methylation and MeHg concentrations in forest soils and stream sediment are not fully understood. In this study, a field investigation was carried out in 4 harvested and 2 unharvested boreal forest watersheds, before and after harvest, to better understand impacts on Hg methylation and MeHg concentration in soils and stream sediment, including their responses to different forest management practices.
View Article and Find Full Text PDFMethyl mercury (MeHg) concentrations in boreal headwater streams are influenced by complex natural processes and disturbances such as forestry management. Understanding drivers of MeHg within boreal streams in Ontario, Canada, is of particular interest as there are legacy MeHg concerns. However, models accounting for the complexity of underlying processes have not yet been developed.
View Article and Find Full Text PDFTerrestrial ecosystems store large amounts of mercury (Hg), which may be subject to methylation, mobilization and uptake into downstream aquatic ecosystems. Mercury concentrations, methylation and demethylation potentials are not well characterized simultaneously across different habitats in boreal forest ecosystems, particularly not so in stream sediment, leading to uncertainties about the importance of various habitats as primary production areas of the bioaccumulative neurotoxin methylmercury (MeHg). In this study, we collected soil and sediment samples from 17 undisturbed, central Canadian boreal forested watersheds during spring, summer and fall to robustly characterize the spatial (upland and riparian/wetland soils, and stream sediment) and seasonal patterns of total Hg (THg) and MeHg concentrations.
View Article and Find Full Text PDFChanges in sulfate (SO) deposition have been linked to changes in mercury (Hg) methylation in peatlands and water quality in freshwater catchments. There is little empirical evidence, however, of how quickly methyl-Hg (MeHg, a bioaccumulative neurotoxin) export from catchments might change with declining SO deposition. Here, we present responses in total Hg (THg), MeHg, total organic carbon, pH, and SO export from a peatland-dominated catchment as a function of changing SO deposition in a long-term (1998-2011), whole-ecosystem, control-impact experiment.
View Article and Find Full Text PDFForest management can alter the mobilization of mercury (Hg) into headwater streams and its conversion to methylmercury (MeHg), the form that bioaccumulates in aquatic biota and biomagnifies through food webs. As headwater streams are important sources of organic materials and nutrients to larger systems, this connectivity may also increase MeHg in downstream biota through direct or indirect effects of forestry on water quality or food web structure. In this study, we collected water, seston, food sources (biofilm, leaves, organic matter), five macroinvertebrate taxa and fish (slimy sculpin; Cottus cognata) at 6 sites representing different stream orders (1-5) within three river basins with different total disturbances from forestry (both harvesting and silviculture).
View Article and Find Full Text PDFSulphate and dissolved organic matter (DOM) in freshwater systems may regulate the formation of methylmercury (MeHg), a potent neurotoxin that biomagnifies in aquatic ecosystems. While many boreal lakes continue to recover from decades of elevated atmospheric sulphate deposition, little research has examined whether historically high sulphate concentrations can result in persistently elevated MeHg production and accumulation in aquatic systems. This study used sediment from a historically sulphate-impacted lake and an adjacent reference lake in northwestern Ontario, Canada to investigate the legacy effects of sulphate pollution, as well as the effects of newly added sulphate, natural organic matter (NOM) of varying sulphur content and a sulphate reducing bacteria (SRB) inhibitor on enhancing or inhibiting the Hg methylation and demethylation activity ( and ) in the sediment.
View Article and Find Full Text PDFHydropower generation, a renewable source of electricity, has been linked to elevated methylmercury (MeHg) concentrations in impoundments and aquatic biota. This study investigates the impact of water level fluctuations (WLF) on MeHg concentrations in water, sediment, and fish. Using a set of controlled microcosm experiments emulating the drawdown/refill dynamics and subsequent sediment exposure to air experienced in reservoirs, we demonstrate that less frequent WLFs, and/or increased exposure of sediment to air, can lead to elevated MeHg concentrations in sediment, and total mercury (THg) and MeHg concentrations in water.
View Article and Find Full Text PDFInhalation of gaseous elemental mercury (GEM) is an occupational exposure concern for workers handling elemental mercury or mercury-containing waste. GEM is also often present near historically mercury-contaminated sites, potentially resulting in low-level, chronic exposure of the wider population. Here we introduce a passive sampler for personal GEM monitoring which combines a radial porous diffusive barrier with an activated carbon sorbent.
View Article and Find Full Text PDFMethylmercury (MeHg) is a bioaccumulative neurotoxin produced by certain sulfate-reducing bacteria and other anaerobic microorganisms. Because microorganisms differ in their capacity to methylate mercury, the abundance and distribution of methylating populations may determine MeHg production in the environment. We compared rates of MeHg production and the distribution of genes in epilimnetic sediments from a freshwater lake that were experimentally amended with sulfate levels from 7 to 300 mg L.
View Article and Find Full Text PDFTracing emission sources and transformations of atmospheric mercury with Hg stable isotopes depends on the ability to collect amounts sufficient for reliable quantification. Commonly employed active sampling methods require power and long pumping times, which limits the ability to deploy in remote locations and at high spatial resolution and can lead to compromised traps. In order to overcome these limitations, we conducted field and laboratory experiments to assess the preservation of isotopic composition during sampling of gaseous elemental mercury (GEM) with a passive air sampler (PAS) that uses a sulfur-impregnated carbon sorbent and a diffusive barrier.
View Article and Find Full Text PDFClimate change is expected to alter the hydrology and vascular plant communities in peatland ecosystems. These changes may have as yet unexplored impacts on peat mercury (Hg) concentrations and net methylmercury (MeHg) production. In this study, peat was collected from PEATcosm, an outdoor, controlled mesocosm experiment where peatland water table regimes and vascular plant functional groups were manipulated over several years to simulate potential climate change effects.
View Article and Find Full Text PDFMethylmercury (MeHg) is a bioaccumulative neurotoxin that is produced by certain anaerobic microorganisms, but the abundance and importance of different methylating populations in the environment is not well understood. We combined mercury geochemistry, hgcA gene cloning, rRNA methods, and metagenomics to compare microbial communities associated with MeHg production in two sulfate-impacted lakes on Minnesota's Mesabi Iron Range. The two lakes represent regional endmembers among sulfate-impacted sites in terms of their dissolved sulfide concentrations and MeHg production potential.
View Article and Find Full Text PDFThe presence of pesticides in streams in winter, five to six years following bans on their municipal use suggests that complicated transport behaviour, such as subsurface retention and/or accumulation of pesticides and its release during storms, could be important for understanding recovery time frames following bans or legislation that aim to reduce chemical inputs. We investigated late fall and winter dynamics of four herbicides in paired urban and rural watersheds in Toronto, Canada during rainfall and snowmelt. The range of average concentrations and loads of the sum of atrazine, metolachlor, 2,4-D and mecoprop overlapped in the two types of watersheds, with slightly higher average concentrations in the rural watershed.
View Article and Find Full Text PDFBenzotriazole UV stabilizers (BT-UVs) have attracted increasing attention due to their bioaccumulative nature and ubiquitous presence in surface waters. We apply high-frequency sampling in paired watersheds to describe, for the first time, the behavior of BT-UVs in stream channels during snowmelt and rainfall. Relative to a largely agricultural watershed, concentrations of BT-UVs in an urban watershed were 4-90 times greater during rainfall and 3-21 times greater during snowmelt.
View Article and Find Full Text PDFThe environmental cycling of mercury (Hg) can be affected by natural and anthropogenic perturbations. Of particular concern is how these disruptions increase mobilization of Hg from sites and alter the formation of monomethylmercury (MeHg), a bioaccumulative form of Hg for humans and wildlife. The scientific community has made significant advances in recent years in understanding the processes contributing to the risk of MeHg in the environment.
View Article and Find Full Text PDFMercury (Hg) methylation is often elevated at the terrestrial-peatland interface, but methylmercury (MeHg) production at this "hot spot" has not been linked with in situ biotic accumulation. We examined total Hg and MeHg levels in peat, invertebrates and tissues of the insectivore Sorex cinereus (masked shrew), inhabiting a terrestrial-peatland ecotone in northern Minnesota, USA. Mean MeHg concentrations in S.
View Article and Find Full Text PDFThough it has been established that stream concentrations of polycyclic aromatic hydrocarbons (PAHs) in urban watersheds can be much greater than those in less developed watersheds, knowledge of transport mechanisms is lacking, particularly in temperate, Northern climates with seasonal snow packs. We combine high-resolution stream water sampling with air, suspended solid and stream flow monitoring to investigate the source to stream transport of PAHs during rainfall and snowmelt in paired watersheds with contrasting land use. Despite similar particle loads, contamination of particles that is 8-48 times higher in the urban watersheds leads to area-normalized loads of PAHs that are 6-82 times greater than in the agricultural watersheds.
View Article and Find Full Text PDFWhile benzotriazoles (BTs) are ubiquitous in urban waters, their sources and transport remain poorly characterized. We aimed to elucidate the origin and hydrological pathways of BTs in Toronto, Canada, by quantifying three BTs, electrical conductivity, and δO in high-frequency streamwater samples taken during two rainfall and one snowmelt event in two watersheds with contrasting levels of urbanization. Average concentrations of total BTs (∑BT) were 1.
View Article and Find Full Text PDFIn low-sulfate and sulfate-limited freshwater sediments, sulfate loading increases the production of methylmercury (MeHg), a potent and bioaccumulative neurotoxin. Sulfate loading to anoxic sediments leads to sulfide production that can inhibit mercury methylation, but this has not been commonly observed in freshwater lakes and wetlands. In this study, sediments were collected from sulfate-impacted, neutral pH, surface water bodies located downstream from ongoing and historic mining activities to examine how chronic sulfate loading produces porewater sulfide, and influences MeHg production and transport.
View Article and Find Full Text PDFEnviron Sci Process Impacts
June 2016
Increased deposition of atmospheric sulfate exacerbates methylmercury (MeHg) production in freshwater wetlands by stimulating methylating bacteria, but it is unclear how methylation in sub-boreal wetlands is impacted by chronically elevated sulfate inputs, such as through mine discharges. The purpose of our study is to determine how sulfate discharges to wetlands from iron mining activities impact MeHg production. In this study, we compare spatial and temporal patterns in MeHg and associated geochemistry in two wetlands receiving contrasting loads of sulfate.
View Article and Find Full Text PDFSoil mercury (Hg) emissions are an important component of the global Hg cycle. Sunlight induced photoreduction of oxidized Hg to gaseous elemental Hg is an important mechanism controlling emissions from the soil surface, however we currently understand little about how subsurface Hg stores participate in gaseous Hg cycling. Our study objective was to investigate the ability of Hg at deeper soil depths to participate in emissions.
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