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Mercury (Hg) is a persistent soil pollutant, and its toxicity can be evaluated using soil enzyme indicators. However, a thorough understanding of how the enzyme resists and remains resilient to Hg stress is essential, as it significantly impacts the accuracy of toxicity assessments. Therefore, it is worthwhile to understand the functional stability of urease in soil under Hg pollution. This study compares the effects of Hg at different concentrations and exposure times on soil urease. Results indicate that soil urease activity was enhanced in the first two hours under low levels of Hg pollution, decreased after six hours of acute Hg pollution, and reached its maximum reduction in 24 hours. The urease in fluvo-aquic soil, with higher soil organic matter showed higher resistance to Hg acute pollution than that in red soil. Over a longer aging process, soil urease activity gradually recovered with time. Hormesis effects were observed in red soil under high Hg stress after 30 days, showing the strong resilience of urease enzyme function to Hg pollution. The ecological dose, ED10, (the Hg concentration causing a 10% reduction in soil urease activity) ranged from 0.09 to 0.59 mg kg−1 under short-term exposure, and was lower than that under a longer aging process (0.28 to 2.71 mg kg−1). Further, aging reduced the Hg ecotoxicity due to decreased Hg availability and the resilience of soil urease activity. This indicates that the risk of Hg pollution estimated by soil urease as an indicator depends on exposure time and enzyme stability. These factors need consideration in heavy metal pollution assessments using soil enzymes. Highlights: Duration of contamination influences the Hg toxicity to soil urease. Short-time exposure to low-level Hg stress exhibited hormesis effect on soil urease. Soil urease resilience potential to Hg pollution depends on soil type. Soil urease shows strong resilience during the aging process in the presence of Hg. [ABSTRACT FROM AUTHOR]

Terrestrial soils in forested landscapes represent some of the largest mercury (Hg) reserves globally. Wildfire can alter the storage and distribution of terrestrial-bound Hg via reemission to the atmosphere or mobilization in watersheds where it may become available for methylation and uptake into food webs. Using data associated with the 2007 Moonlight and Antelope Fires in California, we examined the long-term direct effects of wildfire burn severity on the distribution and magnitude of Hg concentrations in riparian food webs. Additionally, we quantified the cross-ecosystem transfer of Hg from aquatic invertebrate to riparian bird communities; and assessed the influence of biogeochemical, landscape variables, and ecological factors on Hg concentrations in aquatic and terrestrial food webs. Benthic macroinvertebrate methylmercury (MeHg) and riparian bird blood total mercury (THg) concentrations varied by 710- and 760-fold, respectively, and Hg concentrations were highest in predators. We found inconsistent relationships between Hg concentrations across and within taxa and guilds in response to stream chemical parameters and burn severity. Macroinvertebrate scraper MeHg concentrations were influenced by dissolved organic carbon (DOC); however, that relationship was moderated by burn severity (as burn severity increased the effect of DOC declined). Omnivorous bird Hg concentrations declined with increasing burn severity. Overall, taxa more linked to in situ energetic pathways may be more responsive to the biogeochemical processes that influence MeHg cycling. Remarkably, 8 years post-fire, we still observed evidence of burn severity influencing Hg concentrations within riparian food webs, illustrating its overarching role in altering the storage and redistribution of Hg and influencing biogeochemical processes. [ABSTRACT FROM AUTHOR]

Due to its persistence and potential ecological and health impacts, mercury (Hg) is a global pollutant of major concern that may reach high concentrations even in remote polar oceans. In contrast to the Arctic Ocean, studies documenting Hg contamination in the Southern Ocean are spatially restricted and large-scale monitoring is needed. Here, we present the first circumpolar assessment of Hg contamination in Antarctic marine ecosystems. Specifically, the Adélie penguin (Pygoscelis adeliae) was used as a bioindicator species, to examine regional variation across 24 colonies distributed across the entire Antarctic continent. Mercury was measured on body feathers collected from both adults (n = 485) and chicks (n = 48) between 2005 and 2021. Because penguins' diet represents the dominant source of Hg, feather δ13C and δ15N values were measured as proxies of feeding habitat and trophic position. As expected, chicks had lower Hg concentrations (mean ± SD: 0.22 ± 0.08 μg·g‒1) than adults (0.49 ± 0.23 μg·g‒1), likely because of their shorter bioaccumulation period. In adults, spatial variation in feather Hg concentrations was driven by both trophic ecology and colony location. The highest Hg concentrations were observed in the Ross Sea, possibly because of a higher consumption of fish in the diet compared to other sites (krill-dominated diet). Such large-scale assessments are critical to assess the effectiveness of the Minamata Convention on Mercury. Owing to their circumpolar distribution and their ecological role in Antarctic marine ecosystems, Adélie penguins could be valuable bioindicators for tracking spatial and temporal trends of Hg across Antarctic waters in the future. Highlights: Adélie penguins are relevant bioindicators of Hg contamination in Antarctic marine ecosystems. Feather Hg concentrations were measured in 24 breeding colonies (adults and chicks). The highest Hg concentrations were found in the Ross Sea. Both trophic ecology and colony location drove feather Hg concentrations. [ABSTRACT FROM AUTHOR]

The biogeochemistry of tidal marsh sediments facilitates the transformation of mercury (Hg) into the biologically available form methylmercury (MeHg), resulting in elevated Hg exposures to tidal marsh wildlife. Saltmarsh and Acadian Nelson's sparrows (Ammospiza caudacutua and A. nelsoni subvirgatus, respectively) exclusively inhabit tidal marshes, potentially experiencing elevated risk to Hg exposure, and have experienced range-wide population declines. To characterize spatial and temporal variation of Hg exposure in these species, we sampled total mercury (THg) in blood collected from 9 populations spanning 560 km of coastline, including individuals resampled within and among years. Using concurrent nesting studies, we tested whether THg was correlated with nest survival probabilities, an index of fecundity. Blood THg ranged from 0.074–3.373 µg/g ww across 170 samples from 127 individuals. We detected high spatial variability in Hg exposure, observing differences of more than 45-fold across all individuals and 8-fold in mean blood THg among all study plots, including 4-fold between study plots within 4 km. Intraindividual changes in blood Hg exposure did not vary systematically in time but were considerable, varying by up to 2-fold within and among years. Controlling for both species differences and maximum water level, the dominant driver of fecundity in this system, nest survival probability decreased by 10% across the full range of female blood THg concentrations observed. We conclude that Hg has the potential to impair songbird reproduction, potentially exacerbating known climate-change driven population declines from sea-level rise in saltmarsh and Acadian Nelson's sparrows. [ABSTRACT FROM AUTHOR]

Freshwater fish in several regions of New York State (NYS) are known to contain concentrations of mercury (Hg) associated with negative health effects in wildlife and humans. We collected blood and breast feathers from bald eagle (Haliaeetus leucocephalus) nestlings throughout NYS, with an emphasis on the Catskill region to determine their exposure to Hg. We assessed whether habitat type (lake or river), region (Delaware–Catskill region vs. rest of NY) or sample site elevation influenced Hg concentrations in bald eagle breast feathers using ANCOVA. The model was significant and accounted for 41% of the variability in log10 breast feather Hg concentrations. Mercury concentrations in nestling breast feathers were significantly greater in the Delaware–Catskill Region (geometric mean: 14.5 µg/g dw) than in the rest of NY (7.4 µg/g, dw), and greater at nests located at higher elevations. Habitat type (river vs. lake) did not have a significant influence on breast feather Hg concentrations. Geometric mean blood Hg concentrations were significantly greater in Catskill nestlings (0.78 µg/g ww) than in those from the rest of NY (0.32 µg/g). Mercury concentrations in nestling breast feathers and especially blood samples from the Delaware–Catskill region were generally greater than those reported for most populations sampled elsewhere, including areas associated with significant Hg pollution problems. Bald eagles can serve as valuable Hg bioindicators in aquatic ecosystems of NYS, particularly given their broad statewide distribution and their tendency to nest across all major watersheds and different habitat types. [ABSTRACT FROM AUTHOR]

Although reservoir creation increases fish mercury (Hg) concentrations, little information exists on its effects on Hg concentrations in aquatic mammals. River otters (Lontra canadensis) and American mink (Neovison vison) are two aquatic mammals that have been used as model species for assessing Hg bioaccumulation in aquatic systems. We assessed Hg and selenium (Se) concentrations in these two species within and outside of the Williston Reservoir (Peace-Williston (PW) watershed) in northern British Columbia (BC) and used these data to investigate potential explanatory factors (i.e., watershed, gender, trophic level (δ15N), and regional geology) influencing Hg concentrations. Hg concentrations in otter and mink inhabiting the Mackenzie watershed (outside the PW) were significantly lower than other watersheds in Northern BC. The general trend was the same for both species; the Peace-Williston having the highest and Mackenzie having the lowest Hg concentrations. For mink, the Peace-Williston watershed, higher trophic levels, and higher proportions of igneous/metamorphic bedrock were all significant influences on higher Hg concentrations (logistic regression). Higher trophic levels or proportions of of igneous/metamorphic bedrock, however, were not directly associated with the PW watershed suggesting there may be an impoundment effect. Baseline data on natural Hg inputs before planned anthropogenic changes occur is a critical first step to aiding interpretations of Hg-related effects on wildlife populations and their related ecosystems. [ABSTRACT FROM AUTHOR]

In the southeastern Peruvian Amazon, artisanal and small-scale gold mining (ASGM) is estimated to have released up to 300 tonnes of mercury (Hg) to the environment between 1995 and 2007 alone, and is claimed to be responsible for Hg concentrations above international thresholds for aquatic wildlife species. Here, we examined whether Hg concentrations in bat populations are potentially related to regional ASGM-Hg releases. We determined Hg concentrations in the fur of bats collected at three different distances from the major ASGM areas in Peru. Our findings from 204 individuals of 32 species indicate that Hg concentrations in bat fur mainly resulted from differences in feeding habits, because Hg concentrations were significantly higher in omnivorous bats than in frugivorous bats. At least in two species, populations living in ASGM-affected sites harbored higher Hg concentrations than did populations in unaffected sites. Because Hg concentrations reflect Hg dietary exposure, Hg emissions from amalgam roasting sites appear to deposit locally and enter the terrestrial food web. Although our study demonstrates that ASGM activities (and Hg point sources) increase Hg exposure in wildlife, the overall Hg concentrations reported here are relatively low. The measured Hg concentrations were below the toxicity threshold at which adverse neurological effects have been reported in rodents and mink (>10 µg g), and were in the range of Hg concentrations in the fur of bats from nonpoint source affected sites in other latitudes. This study emphasizes the importance of considering feeding habits when evaluating Hg concentrations in bats and other vertebrates. [ABSTRACT FROM AUTHOR]

Temporal trends in Hg concentrations were investigated in primary flight feathers from 319 specimens of three birds of prey: P7 in the northern goshawk ( Accipiter gentilis), P6 in the common buzzard (Buteo buteo) and P5 in the tawny owl (Strix aluco). The samples were stored in a regional environmental specimen bank and belonged to specimens which died between 2000 and 2013 in Galicia (NW Spain). We would expect to see a decline in Hg concentrations across the study period, as data of atmospheric emissions show a gradual reduction of this pollutant in Europe in the last two decades. The study did not reveal any temporal pattern in Hg concentrations of feathers in any of the three species for the study period, may be due to the persistence of Hg in the environment, but showed a low level of contamination by this metal in the study area. In addition, the results show high intra-specific, as well as, inter-annual and inter-specific variability in data, mainly attributed to the level of exposure of the raptors to this pollutant and to the biomagnification process of Hg through food chains. These findings indicate that the high variability can be a limiting factor in the use of raptors for biomonitoring temporal patterns of Hg, but nevertheless, the technique provides qualitative information about the amount of Hg that reach the top of the terrestrial food chains. [ABSTRACT FROM AUTHOR]

This study examines mercury exposure in bats across the northeast U.S. from 2005 to 2009. We collected 1,481 fur and 681 blood samples from 8 states and analyzed them for total Hg. A subset ( n = 20) are also analyzed for methylmercury (MeHg). Ten species of bats from the northeast U.S. are represented in this study of which two are protected by the Endangered Species Act (ESA 1973) and two other species are pending review. There are four objectives in this paper: (1) to examine correlates to differences in fur-Hg levels among all of the sampling sites, including age, sex, species, and presence of a Hg point source; (2) define the relationship between blood and fur-Hg levels and the factors that influence that relationship including age, sex, species, reproductive status, and energetic condition; (3) determine the relationships between total Hg and MeHg in five common eastern bat species; and (4) assess the distribution of Hg across bat populations in the northeast. We found total blood and fur mercury was eight times higher in bats captured near point sources compared to nonpoint sources. Blood-Hg and fur-Hg were well correlated with females on average accumulating two times more Hg in fur than males. On average fur MeHg accounted for 86 % (range 71-95 %) of the total Hg in bat fur. Considering that females had high Hg concentrations, beyond that of established levels of concern, suggests there could be negative implications for bat populations from high Hg exposure since Hg is readily transferred to pups via breast milk. Bats provide an integral part of the ecosystem and their protection is considered to be of high priority. More research is needed to determine if Hg is a stressor that is negatively impacting bat populations. [ABSTRACT FROM AUTHOR]

We captured Nelson's, Saltmarsh and Seaside Sparrows ( Ammodramus nelsoni, A. caudacutus and A. maritimus) at three salt marsh sites near Wrightsville Beach, North Carolina during five non-breeding seasons (September through April, 2006-2011). We analyzed breast feather samples from all of these seasons and blood and first primary feather (P1) samples from three seasons (2008-2011) for mercury (Hg). Generalized linear models were used to test for the impact of species, season, site and month on blood Hg, species, season and site on P1 Hg and species and season on breast feather Hg. The best-fit model for blood indicated that Hg varied among species, seasons and months. Saltmarsh Sparrows maintain higher blood Hg than Nelson's and Seaside Sparrows during the non-breeding season while they are feeding in mixed flocks. In Nelson's and Seaside Sparrows, blood Hg decreased during mid-winter compared to early fall and late spring. Breast feather and P1 Hg varied among species with Saltmarsh Sparrows exhibiting higher concentrations than the other two species, while Nelson's Sparrows had lower concentrations than the other two species. Breast feather Hg was higher in the final three seasons than in the first two. Our results indicate that Hg exposure on breeding sites may be increasing and that high levels of Hg exposure during the breeding season may affect blood Hg concentrations year-round in Saltmarsh Sparrows. Our data thus provide a baseline for future Hg assessments in these species in NC. [ABSTRACT FROM AUTHOR]

Bald eagles ( Haliaeetus leucocephalus) have been utilized as a biosentinel of aquatic ecosystem health in the Great Lakes Region since the early 1960s. Bald eagle populations have been monitored at Voyageurs National Park (VNP), Minnesota, since 1973. For the past 20 years, researchers have collected feathers from nestling bald eagles to assess their dietary exposure to mercury (Hg) on Rainy, Kabetogama, and Namakan lakes in VNP. Mercury is an environmental pollutant with both natural and anthropogenic sources, and negatively affects many species of wildlife. In a previous study, geometric mean concentrations of Hg in feathers of nestling bald eagles were greater at VNP (20 mg/kg Dry Weight (DW)) than in nestling feathers from other Great Lakes subpopulations (~7 mg/kg DW), for the period 1985-1989. Current geometric mean concentrations have declined by 77.4% since 1989 at VNP. While all samples from 1985 to 1989 had detectable concentrations of Hg, 10% of current samples had concentrations below the reportable detection limit (0.001 mg/kg DW, n = 180). The major lakes at VNP are impounded, and Hg concentrations also declined greatly after the lake level stabilization order by the International Joint Commission was implemented in 1999. Mercury concentrations in feathers of nestling bald eagles from 1989 to 2010 ranged from ND (<0.001) to 34.97 mg/kg DW. The highest single concentration in a nestling was from Namakan Lake in 2010. The five-year geometric means for Rainy, Kabetogama, and Namakan lakes for 2006-2010 were 6.08, 1.07, and 5.56 mg/kg DW ( n = 28, n = 32, n = 27) respectively. Although Hg concentrations in feathers of nestlings greatly declined after the change in water level management in 1999 and are lower than 1989 concentrations, recent samples suggest a gradual increase. Continued monitoring of nestling feather concentrations will be essential to assess this increase, to determine the source of Hg, to determine if there are changes to methylation potential, and to evaluate and optimize water level management. [ABSTRACT FROM AUTHOR]

Regular annual flooding of the Amazonian rivers changes the aquatic environment affecting fish feeding strategies. The Rio Madeira has been greatly impacted by deforestation for agricultural projects, damming for a hydroelectric power plant, and alluvial gold extraction. We studied fish-Hg concentrations within defined weight ranges of representative species at the top of the food web, comparing high and low water seasons. Selected piscivorous species (Cichla spp, Hoplias malabaricus, Pinirampus pirinampu, Serrasalmus spp) showed a large variation of Hg concentrations but only "traíra" (Hoplias malabaricus) showed a statistically significant difference between seasons. However, the bioaccumulation trends during high and low waters were similar for "tucunaré" (Cichla spp) and "traíra" (Hoplias malabaricus) but different for "piranhas" (Serrasalmus spp), "barba chata" (Pinirampus pirinampu) and the detritivorous Prochilodus nigricans. Fish-Hg bioaccumulation is species specific; changes in feeding strategies brought by flooding seasons can change the bioaccumulation pattern without systematically affecting the overall accrual of methylmercury in tertiary consumer species. It appears that naturally occurring Hg and the high sediment load of the Rio Madeira are secondary factors in the Hg bioaccumulation pattern of fish species at the top of the food chain. [ABSTRACT FROM AUTHOR]