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USGS2017

Maternal transfer of mercury to songbird eggs

We evaluated the maternal transfer of mercury to eggs in songbirds, determined whether this relationship differed between songbird species, and developed equations for predicting mercury concentrations in eggs from maternal blood. We sampled blood and feathers from 44 house wren ( Troglodytes aedon ) and 34 tree swallow ( Tachycineta bicolor ) mothers and collected their full clutches ( n = 476 eggs) within 3 days of clutch completion. Additionally, we sampled blood and feathers from 53 tree swallow mothers and randomly collected one egg from their clutches ( n = 53 eggs) during mid to late incubation (6–10 days incubated) to evaluate whether the relationship varied with the timing of sampling the mother's blood. Mercury concentrations in eggs were positively correlated with mercury concentrations in maternal blood sampled at (1) the time of clutch completion for both house wrens ( R 2 = 0.97) and tree swallows ( R 2 = 0.97) and (2) during mid to late incubation for tree swallows ( R 2 = 0.71). The relationship between mercury concentrations in eggs and maternal blood did not differ with the stage of incubation when maternal blood was sampled. Importantly, the proportion of mercury transferred from mothers to their eggs decreased substantially with increasing blood mercury concentrations in tree swallows, but increased slightly with increasing blood mercury concentrations in house wrens. Additionally, the proportion of mercury transferred to eggs at the same maternal blood mercury concentration differed between species. Specifically, tree swallow mothers transferred 17%–107% more mercury to their eggs than house wren mothers over the observed mercury concentrations in maternal blood (0.15–1.92 μg/g ww). In contrast, mercury concentrations in eggs were not correlated with those in maternal feathers and, likewise, mercury concentrations in maternal blood were not correlated with those in feathers (all R 2 < 0.01). We provide equations to translate mercury concentrations from maternal blood to eggs (and vice versa), which should facilitate comparisons among studies and help integrate toxicity benchmarks into a common tissue.

California↗

USGS2020

Disentangling the effects of habitat biogeochemistry, food web structure, and diet composition on mercury bioaccumulation in a wetland bird

Methylmercury (MeHg) is a globally pervasive contaminant with known toxicity to humans and wildlife. Several sources of variation can lead to spatial differences in MeHg bioaccumulation within a species including: biogeochemical processes that influence MeHg production and availability within an organism’s home range; trophic positions of consumers and MeHg biomagnification efficiency in food webs; and individual prey preferences that influence diet composition. To better understand spatial variation in MeHg bioaccumulation within a species, we evaluated the effects of habitat biogeochemistry, food web structure, and diet composition in the wetland-obligate California black rail ( Laterallus jamaicensis coturniculus ) at three wetlands along the Petaluma River in northern San Francisco Bay, California, USA. The concentration of MeHg in sediments differed significantly among wetlands. We identified three sediment and porewater measurements that contributed significantly to a discriminant function explaining differences in habitat biogeochemistry among wetlands: the porewater concentration of ferrous iron, the percent organic matter, and the sediment MeHg concentration. Food web structure and biomagnification efficiency were similar among wetlands, with trophic magnification factors for MeHg ranging from 1.84 to 2.59. In addition, regurgitation samples indicated that black rails were dietary generalists with similar diets among wetlands (percent similarity indices > 70%). Given the similarities in diet composition, food web structure, and MeHg biomagnification efficiency among wetlands, we concluded that variation in habitat biogeochemistry and associated sediment MeHg production was the primary driver of differences in MeHg concentrations among black rails from different wetlands.

California↗

USGS2020

Arsenic-related oxidative stress in experimentally dosed wild great tit nestlings

Arsenic (As) is broadly distributed due to natural and anthropogenic sources, and it may cause adverse effects in birds. However, research on other elements (Pb, Hg and Cd) has been prioritized, resulting in scarce data on As exposure and related effects in wild birds. One of the mechanisms responsible for As toxicity is oxidative stress. Therefore, the aim of this study was to investigate if environmentally relevant As levels affected oxidative stress biomarkers in great tits ( Parus major ). This is the first field experiment studying the effects of As on oxidative stress in wild passerines. Wild great tit nestlings were orally dosed with sodium arsenite (Control: water, Low dose: 0.2 μg g −1 d −1 and High dose: 1 μg g −1 d −1 ; from day 3 to day 13 post-hatching). We intended to reach As concentrations similar to those at which passerines are exposed to at actual polluted areas. We compared the responses to the experimental manipulations (High, Low and Control groups) with those in an As/metal-exposed population breeding close to a Cu–Ni smelter in Finland (Smelter group). A set of antioxidants (tGSH, GSH:GSSG ratio, CAT, SOD, GST and GPx), and oxidative damage biomarkers (lipid peroxidation, protein carbonylation, 8-hydroxy-2′-deoxyguanosine formation in DNA, and telomere length) were explored in blood. Arsenic administration had no significant effect on most of the biomarkers measured: only the CAT activity was lower in the High As group and the GPx activity was enhanced in the Smelter group compared to the Control. Our results suggest that the dose and duration of the As exposure was not enough to induce oxidative damage in red cells of great tit nestlings. In spite of this, nestlings dosed with 1 μg g −1 d −1 of sodium arsenite showed non-significantly higher oxidative stress biomarkers than controls, suggesting that we were close to an effect level for the redox-defense system. Oxidative effects at equivalent As levels combined with other stressors cannot be dismissed.

Harjavalta↗

USGS2021

Effect of organic matter concentration and characteristics on mercury mobilization and methylmercury production at an abandoned mine site

Thousands of abandoned mines throughout the western region of North America contain elevated total-mercury (THg) concentrations. Mercury is mobilized from these sites primarily due to erosion of particulate-bound Hg (THg-P). Organic matter-based soil amendments can promote vegetation growth on mine tailings, reducing erosion and subsequent loading of THg-P into downstream waterbodies. However, the introduction of a labile carbon source may stimulate microbial activity that can produce methylmercury (MeHg)—the more toxic and bioaccumulative form of Hg. Our objectives were to investigate how additions of different organic matter substrates impact Hg mobilization and methylation using a combination of field observations and controlled experiments. Field measurements of water, sediment, and porewater were collected downstream of the site and multi-year monitoring (and load calculations) were conducted at a downstream gaging station. MeHg production was assessed using stable isotope methylation assays and mesocosm experiments that were conducted using different types of organic carbon soil amendments mixed with materials from the mine site. The results showed that >80% of the THg mobilized from the mine was bound to particles and that >90% of the annual Hg loading occurred during the period of elevated discharge during spring snowmelt. Methylation rates varied between different types of soil amendments and were correlated with the components of excitation emission matrices (EEMs) associated with humic acid fractions of organic matter. The mesocosm experiments showed that under anoxic conditions carbon amendments to tailings could significantly increase porewater MeHg concentrations (up to 13 ± 3 ng/L). In addition, the carbon amendments significantly increased THg partitioning into porewater. Overall, these results indicate that soil amendment applications to reduce surface erosion at abandoned mine sites could be effective at reducing particulate Hg mobilization to downstream waterbodies; however, some types of carbon amendments can significantly increase Hg methylation as well as increase the mobilization of dissolved THg from the site.

Idaho↗

USGS2021

Regional target loads of atmospheric nitrogen and sulfur deposition for the protection of stream and watershed soil resources of the Adirondack Mountains, USA

Acidic deposition contributes to a range of environmental impacts across forested landscapes, including acidification of soil and drainage water, toxic aluminum mobilization, depletion of available soil nutrient cations, and impacts to forest and aquatic species health and biodiversity. In response to decreasing levels of acidic deposition, soils and drainage waters in some regions of North America have become gradually less acidic. Thresholds of atmospheric deposition at which adverse ecological effects are manifested are called critical loads (CLs) and/or target loads (TLs). Target loads are developed based on approaches that account for spatial and temporal aspects of acidification and recovery. Exceedance represents the extent to which current or projected future levels of acidic deposition exceed the level expected to cause ecological harm. We report TLs of sulfur (S) and nitrogen (N) deposition and the potential for ecosystem recovery of watershed soils and streams in the Adirondack region of New York State, resources that have been less thoroughly investigated than lakes. Regional TLs were calculated by statistical extrapolation of hindcast and forecast simulations of 25 watersheds using the process-based model PnET-BGC coupled with empirical observations of stream hydrology and established sensitivity of sugar maple ( Acer saccharum ) to soil base saturation and brook trout ( Salvelinus fontinalis ) to stream acid neutralizing capacity (ANC). Historical impacts and the expected recovery timeline of regional soil and stream chemistry and fish community condition within the Adirondack Park were evaluated. Analysis suggests that many low-order Adirondack streams and associated watershed soils have low TLs (<40 meq/m 2 /yr of N+S deposition) to achieve specified benchmarks for recovery of soil base saturation or stream ANC. Acid-sensitive headwater and low-order streams and watershed soils in the region are expected to experience continued adverse effects from N and S deposition well into the future even under aggressive emissions reductions. Watershed soils and streams in the western Adirondack Park are particularly vulnerable to acidic deposition and currently in exceedance of TLs. The methods used for linking statistical and process-based models to consider chemical and biological response under varying flow conditions at the regional scale in this study can be applied to other areas of concern.

New York↗

USGS2022

Using tissue cysteine to predict the trophic transfer of methylmercury and selenium in lake food webs

The biomagnification of toxic methylmercury (MeHg) and selenium (Se) through aquatic food webs using nitrogen stable isotopes (δ 15 N) varies among ecosystems but underlying mechanisms are yet unexplained. Given the strong links between MeHg and thiol-containing amino acids and proteins containing selenocysteine, our hypothesis was that cysteine content is a better predictor of MeHg and Se transfer through lake food webs than δ 15 N. Food web samples were collected from six lakes in Kejimkujik National Park, Nova Scotia, Canada, and the regression slopes of log MeHg or Se versus protein-bound cysteine or bulk δ 15 N were compared. Across all six lakes, MeHg varied by a factor of 10 among taxa and was significantly and positively related to both cysteine (R 2 = 0.65–0.80, p < 0.001) and δ 15 N (R 2 = 0.88–0.94, p < 0.001), with no among-system differences in these slopes. In contrast, total Se concentrations varied by less than a factor of 2 among taxa in four lakes and were significantly related to cysteine in only two food webs (R 2 = 0.20 & 0.37, p = 0.014 & < 0.001); however, δ 15 N was not a predictor of Se in any lake (p = 0.052–0.777). Overall, these novel results indicate that cysteine content predicts MeHg, and sometimes Se, across trophic levels, providing a potential mechanism for among-system differences in their biomagnification.

Environmental Pollution↗

USGS2023

Anticoagulant rodenticides are associated with increased stress and reduced body condition of avian scavengers in the Pacific Northwest

Anticoagulant rodenticides (AR) have been used globally to manage commensal rodents for decades. However their application has also resulted in primary, secondary, and tertiary poisoning in wildlife. Widespread exposure to ARs (primarily second generation ARs; SGARs) in raptors and avian scavengers has triggered considerable conservation concern over their potential effects on populations. To identify risk to extant raptor and avian scavenger populations in Oregon and potential future risk to the California condor ( Gymnogyps californianus ) flock recently established in northern California, we assessed AR exposure and physiological responses in two avian scavenger species (common ravens [ Corvus corax ] and turkey vultures [ Cathartes aura ]) throughout Oregon between 2013 and 2019. AR exposure was widespread with 51% (35/68) of common ravens and 86% (63/73) of turkey vultures containing AR residues. The more acutely toxic SGAR brodifacoum was present in 83% and 90% of AR exposed common ravens and turkey vultures. The odds of AR exposure in common ravens were 4.7-fold higher along the coastal region compared to interior Oregon. For common ravens and turkey vultures that were exposed to ARs, respectively, 54% and 56% had concentrations that exceeded the 5% probability of toxicosis (>20 ng/g ww; Thomas et al., 2011), and 20% and 5% exceeded the 20% probability of toxicosis (>80 ng/g ww; Thomas et al., 2011). Common ravens exhibited a physiological response to AR exposure with fecal corticosterone metabolites increasing with sum ARs (ΣAR) concentrations. Both female common raven and turkey vultures’ body condition was negatively correlated with increasing ΣAR concentrations. Our results suggest avian scavengers in Oregon are experiencing extensive AR exposure and the newly established population of California condors in northern California may experience similar AR exposure if they feed in southern Oregon. Understanding the sources of ARs across the landscape is an important first step in reducing or eliminating AR exposure in avian scavengers.

Oregon↗

USGS2026

Selenium and mercury tissue partitioning and trophodynamics in the Lake Koocanusa (USA–Canada) fish community

Mining-related contaminants such as selenium (Se) and mercury (Hg) accumulate in aquatic organisms and transfer through aquatic food webs, where they can exert toxic effect undermining the ecological health of aquatic resources. Yet, how Se and Hg co-distribute within food webs and within individual organisms remains poorly understood. We compiled muscle and ovary Se and Hg concentration data from fishes captured in Lake Koocanusa—a North American reservoir receiving elevated Se and Hg inputs from coal mining operations in the Elk River Valley, Canada—to provide insights into the co-processing of Se and Hg within fish and among fish species, including how ecological or seasonal factors shift these distribution patterns. Se and Hg concentrations (ranges: 0.21–38.7 μg Se g −1 dry weight and 0.01–0.84 μg Hg g −1 wet weight), as well as Se:Hg molar ratios, varied substantially between tissues and among species, reflecting biological and ecological differences. Our results suggest that the decoupling of Se or Hg deposition in fish muscle versus ovary may reflect different pathways of impairment, at the individual and population levels, and that interspecific and tissue-specific variability makes it challenging to set a universal Se:Hg threshold for the protection of aquatic organisms.

British Columbia, Montana↗

USGS2023

Cross-sectional associations between drinking water arsenic and urinary inorganic arsenic in the US: NHANES 2003-2014

Background: Inorganic arsenic is a potent carcinogen and toxicant associated with numerous adverse health outcomes. The contribution of drinking water from private wells and regulated community water systems (CWSs) to total inorganic arsenic exposure is not clear. Objectives: To determine the association between drinking water arsenic estimates and urinary arsenic concentrations in the 2003-2014 National Health and Nutrition Examination Survey (NHANES). Methods: We evaluated 11,088 participants from the 2003-2014 NHANES cycles. For each participant, we assigned private well and CWS arsenic levels according to county of residence using estimates previously derived by the US Environmental Protection Agency and US Geological Survey. We used recalibrated urinary dimethylarsinate (rDMA) to reflect the internal dose of estimated water arsenic by applying a previously validated, residual-based method that removes the contribution of dietary arsenic sources. We compared the adjusted geometric mean ratios and corresponding percent change of urinary rDMA across tertiles of private well and CWS arsenic levels, with the lowest tertile as the reference. Comparisons were made overall and stratified by census region and race/ethnicity. Results: Overall, the geometric mean of urinary rDMA was 2.52 (2.30, 2.77) µg/L among private well users and 2.64 (2.57, 2.72) µg/L among CWS users. Urinary rDMA was highest among participants in the West and South, and among Mexican American, Other Hispanic, and Non-Hispanic Other participants. Urinary rDMA levels were 25% (95% CI: 17-34%) and 20% (95% CI: 12-29%) higher comparing the highest to the lowest tertile of CWS and private well arsenic, respectively. The strongest associations between water arsenic and urinary rDMA were observed among participants in the South, West, and among Mexican American and Non-Hispanic White and Black participants. Discussion: Both private wells and regulated CWSs are associated with inorganic arsenic internal dose as reflected in urine in the general US population.

Environmental Research↗

USGS2026

Effects of carbamazepine to visual function in early life stage fish

The frequent detection of pharmaceuticals and personal care products (PPCPs) in the environment raises concern for aquatic systems. Carbamazepine (CBZ), an antiepileptic drug, is among the most detected PPCP globally, with concentrations in surface water exceeding those that induce toxicity to aquatic organisms. Non-targeted transcriptomic profiling was conducted in zebrafish ( Danio rerio ) larvae exposed to 0, 1, 5, 10, or 50 μg/L CBZ from 2 h post fertilization (hpf) through hatching, and then sampled at 48, 72, or 144 hpf. Transcriptomic profiles were annotated and characterized with in silico bioinformatic software to assess top enriched pathways and identify targets of environmentally relevant concentrations of CBZ and anchor molecular effects to higher levels of biological organization. Based on this analysis, CBZ was predicted to impair visual perception and sensory system development. The number of eye saccades, determined with a visually mediated behavioral assay, optokinetic response, was significantly reduced in 144 hpf larvae exposed to concentrations as low as 1 μg/L CBZ. These results indicate that environmentally relevant concentrations of CBZ may target and impact processes involved in visual function in fish.

Environmental Research↗

USGS2026

PFAS contamination in Florida estuarine fishes: Levels, patterns, and estimated human and ecological health risks

Per- and polyfluoroalkyl substances (PFAS) pose a significant health threat due to their environmental persistence and toxicity. While PFAS contamination is widespread in Florida, the state currently lacks fish consumption advisories (FCAs) for these compounds, despite existing FCAs for legacy pollutants. This study quantified 40 PFAS in edible muscle tissue from 264 fish (16 species) across four estuaries along Florida's Atlantic coast to assess ecological and human health risks. The highest concentrations of total PFAS were found in Red Drum ( Sciaenops ocellatus ; 0.209 – 51.6 ng/g wet weight) and Spotted Seatrout ( Cynoscion nebulosus; 2.01 – 24.3 ng/g ww) in the Indian River Lagoon, where up to 68% of Red Drum and 75% of Spotted Seatrout exceeded ecological quality standards, indicating potential impacts on predators. PFOS was the predominant PFAS, driving ecological and human health risks. Estimated daily intakes (EDIs) of PFOS exceeded the EPA reference dose (RfD) by up to 3 orders of magnitude, with the highest exposures concentrated in Red Drum and Spotted Seatrout from the Indian River Lagoon. These findings highlight that PFAS monitoring of tissue concentrations in fish across Florida's freshwater and marine systems would be needed for accurately quantifying exposure risks. Such efforts are fundamental to informing regulatory frameworks regarding FCAs and ensuring the long-term protection of aquatic ecosystems and human health.

Florida↗

USGS2006

Effects of polychlorinated biphenyls, hexachlorocyclohexanes, and mercury on human neutrophil apoptosis, actin cytoskelton, and oxidative state

Apoptosis, or programmed cell death, has been proposed as a biomarker for environmental contaminant effects. In this work, we test the hypothesis that in vitro assays of apoptosis are sensitive indicators of immunological effects of polychlorinated biphenyls, hexachlorocyclohexanes, and mercury on human neutrophils. Apoptosis, necrosis, and viability as well as the related indicators F-actin levels, and active thiol state were measured in purified human neutrophils after treatment with contaminants. Effective concentrations observed were 0.3 μM (60 μg/L) mercury, 750 μg/L Aroclor 1254, and 50 μM (14,500 μg/L) hexachlorocylcohexanes. Concentrations of contaminants that induced apoptosis also decreased cellular F-actin levels. Active thiols were altered by mercury, but not organochlorines. Comparison of these data with levels of contaminants reported to be threats to human health indicate neutrophil apoptosis is a sensitive indicator of mercury toxicity.

Environmental Toxicology and Pharmacology↗

USGS2004

The microbial arsenic cycle in Mono Lake, California

Significant concentrations of dissolved inorganic arsenic can be found in the waters of a number of lakes located in the western USA and in other water bodies around the world. These lakes are often situated in arid, volcanic terrain. The highest concentrations of arsenic occur in hypersaline, closed basin soda lakes and their remnant brines. Although arsenic is a well-known toxicant to eukaryotes and prokaryotes alike, some prokaryotes have evolved biochemical mechanisms to exploit arsenic oxyanions (i.e., arsenate and arsenite); they can use them either as an electron acceptor for anaerobic respiration (arsenate), or as an electron donor (arsenite) to support chemoautotrophic fixation of CO 2 into cell carbon. Unlike in freshwater or marine ecosystems, these processes may assume quantitative significance with respect to the carbon cycle in arsenic-rich soda lakes. For the past several years our research has focused on the occurrence and biogeochemical manifestations of these processes in Mono Lake, a particularly arsenic-rich environment. Herein we review some of our findings concerning the biogeochemical arsenic cycle in this lake, with the hope that it may broaden the understanding of the influence of microorganisms upon the speciation of arsenic in more common, less “extreme” environments, such as drinking water aquifers.

California↗

USGS2020

Trace and rare earth elements determination in milk whey from the Veneto region, Italy

Multi-element analyses determine the content of 17 trace elements (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Cd, Cs, Ba, Pb, U) and 14 rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y) in whey samples from cow and goat milk by inductively coupled plasma mass spectrometry and inductively coupled plasma-sector field mass spectrometry. A total of 261 milk whey samples were collected from four locations in the Veneto region of northeastern (NE) Italy. These samples contain a wide range concentration of 17 trace elements (0.06–1530 μg kg −1 ) and 14 rare earth elements (0.16–28.2 ng kg −1 ) in whey samples, but do not reach toxic concentrations. Elemental fingerprinting of trace and rare earth elements in cow and goat milk whey provide information on the dairy quality and, as they reflect the local environmental conditions, result in an excellent indicator of their geographical origin.

Veneto region↗

USGS2006

Speciation of volatile arsenic at geothermal features in Yellowstone National Park

Geothermal features in the Yellowstone National Park contain up to several milligram per liter of aqueous arsenic. Part of this arsenic is volatilized and released into the atmosphere. Total volatile arsenic concentrations of 0.5–200 mg/m 3 at the surface of the hot springs were found to exceed the previously assumed nanogram per cubic meter range of background concentrations by orders of magnitude. Speciation of the volatile arsenic was performed using solid-phase micro-extraction fibers with analysis by GC–MS. The arsenic species most frequently identified in the samples is (CH 3 ) 2 AsCl, followed by (CH 3 ) 3 As, (CH 3 ) 2 AsSCH 3 , and CH 3 AsCl 2 in decreasing order of frequency. This report contains the first documented occurrence of chloro- and thioarsines in a natural environment. Toxicity, mobility, and degradation products are unknown.

Idaho, Montana, Wyoming↗

USGS2010

Rate of formation and dissolution of mercury sulfide nanoparticles: The dual role of natural organic matter

Mercury is a global contaminant of concern due to its transformation by microorganisms to form methylmercury, a toxic species that accumulates in biological tissues. The effect of dissolved organic matter (DOM) isolated from natural waters on reactions between mercury(II) (Hg) and sulfide (S(-II)) to form HgS (s) nanoparticles across a range of Hg and S(-II) concentrations was investigated. Hg was equilibrated with DOM, after which S(-II) was added. Dissolved Hg (Hg aq ) was periodically quantified using ultracentrifugation and chemical analysis following the addition of S(-II). Particle size and identity were determined using dynamic light scattering and X-ray absorption spectroscopy. S(-II) reacts with Hg to form 20 to 200nm aggregates consisting of 1-2 nm HgS (s) subunits that are more structurally disordered than metacinnabar in the presence of 2 x 10 -9 to 8 x 10 -6 M Hg and 10 (mg C)L -1 DOM. Some of the HgS(s) nanoparticle aggregates are subsequently dissolved by DOM and (re)precipitated by S(-II) over periods of hours to days. At least three fractions of Hg-DOM species were observed with respect to reactivity toward S(-II): 0.3 μmol reactive Hg per mmol C (60 percent), 0.1 μmol per mmol C (20 percent) that are kinetically hindered, and another 0.1 μmol Hg per mmol C (20 percent) that are inert to reaction with S(-II). Following an initial S(-II)-driven precipitation of HgS (s) , HgS (s) was dissolved by DOM or organic sulfur compounds. HgS (s) formation during this second phase was counterintuitively favored by lower S(-II) concentrations, suggesting surface association of DOM moieties that are less capable of dissolving HgS (s) . DOM partially inhibits HgS(s) formation and mediates reactions between Hg and S(-II) such that HgS (s) is susceptible to dissolution. These findings indicate that Hg accessibility to microorganisms could be controlled by kinetic (intermediate) species in the presence of S(-II) and DOM, undermining the premise that equilibrium Hg species distributions should correlate to the extent or rate of Hg methylation in soils and sediments.

Geochimica et Cosmochimica Acta↗

USGS2012

Oxygen and sulfur isotope systematics of sulfate produced during abiotic and bacterial oxidation of sphalerite and elemental sulfur

Studies of metal sulfide oxidation in acid mine drainage (AMD) systems have primarily focused on pyrite oxidation, although acid soluble sulfides (e.g., ZnS) are predominantly responsible for the release of toxic metals. We conducted a series of biological and abiotic laboratory oxidation experiments with pure and Fe-bearing sphalerite (ZnS & Zn 0.88 Fe 0.12 S), respectively, in order to better understand the effects of sulfide mineralogy and associated biogeochemical controls of oxidation on the resultant δ 34 S and δ 18 O values of the sulfate produced. The minerals were incubated in the presence and absence of Acidithiobacillus ferrooxidans at an initial solution pH of 3 and with water of varying δ 18 O values to determine the relative contributions of H 2 O-derived and O 2 -derived oxygen in the newly formed sulfate. . Experiments were conducted under aerobic and anaerobic conditions using O 2 and Fe(III) aq as the oxidants, respectively. Aerobic incubations with A. ferrooxidans , and S o as the sole energy source were also conducted. The δ 34 S SO 4 "> δ34SSO4 values from both the biological and abiotic oxidation of ZnS and ZnS Fe by Fe(III) aq produced sulfur isotope fractionations ( ε 34 S SO 4 - ZnS "> ε34SSO4-ZnS ) of up to −2.6‰, suggesting the accumulation of sulfur intermediates during incomplete oxidation of the sulfide. No significant sulfur isotope fractionation was observed from any of the aerobic experiments. Negative sulfur isotope enrichment factors ( ε 34 S SO 4 - ZnS "> ε34SSO4-ZnS ) in AMD systems could reflect anaerobic, rather than aerobic pathways of oxidation. During the biological and abiotic oxidation of ZnS and ZnS Fe by Fe(III) aq all of the sulfate oxygen was derived from water, with measured ε 18 O SO 4 - H 2 O "> ε18OSO4-H2O values of 8.2 ± 0.2‰ and 7.5 ± 0.1‰, respectively. Also, during the aerobic oxidation of ZnS Fe and S o by A . ferrooxidans , all of the sulfate oxygen was derived from water with similar measured ε 18 O SO 4 - H 2 O "> ε18OSO4-H2O values of 8.1 ± 0.1‰ and 8.3 ± 0.3‰, respectively. During biological oxidation of ZnS by O 2 , an estimated 8% of sulfate–oxygen was derived from O 2 , which is enriched in 18 O relative to water, thus resulting in a larger apparent ε 18 O SO 4 - H 2 O "> ε18OSO4-H2O value of 9.5‰. Based on the data presented we hypothesize that the similar ε 18 O SO 4 - H 2 O "> ε18OSO4-H2O values of ∼8‰ from all of the aerobic and anaerobic experiments result from a common rate-limiting step that involves oxygen isotopic exchange between a sulfite ( SO 3 - "> SO3- ) intermediate and H 2 O. Our results indicate that the δ 18 O SO 4 "> δ18OSO4 values cannot be used to distinguish biological and abiotic, nor aerobic versus anaerobic, pathways of sphalerite oxidation. However, the ε 18 O SO 4 - H 2 O "> ε18OSO4-H2O values of ∼8‰ measured here are distinctly higher than ε 18 O SO 4 - H 2 O "> ε18OSO4-H2O values of ∼4‰ previously reported for pyrite oxidation indicating the influence of sulfide mineralogy on measured δ 18 O SO 4 "> δ18OSO4 values.

Geochimica et Cosmochimica Acta↗

USGS2020

Behavior, size, and body condition predict susceptibility to management and reflect post-treatment frequency shifts in an invasive snake

Foraging behavior can have population-level effects that are of interest for wildlife management. For invasive species, foraging behavior has been tied to establishment ability and rate of spread and is generally of import in understanding invasion biology. A major method for controlling invasive vertebrates is using food-based baits as attractants. Tool efficacy is therefore partially driven by individual decision-making during foraging, which may also affect population response to control. We used three studies on the invasive, arboreal brown treesnake ( Boiga irregularis ) on Guam to measure 1) size, body condition, and behavioral correlates with mortality in response to control using toxic baits, 2) shifts in prevalence of those traits after control treatments occurred and, based on the prior two findings, 3) interactive relationships between size, body condition, and behavioral traits at the landscape scale for untreated populations. Each trait was selected due to a potential relationship with foraging behavior or energetic state of an arboreal snake, as a method to estimate how foraging behavior can inform control tool efficacy. We found that snakes were more likely to be killed by toxiic baits if they had a lower body weight, were more active leading up to a bait application, and encountered on the ground more frequently. Across two treated populations, both body size and condition of sampled snakes increased after treatment, while the incidence of ground encounters decreased. Throughout forested habitat on Guam, ground encounter probability was positively correlated with snake size and inversely correlated to body condition. Additionally, size and condition had interactive effects such that snakes in good condition were more arboreal. Thus, body size and behavior (ground encounters) correlated with control-tool susceptibility and frequency shifts occurred in those traits within sampled post-treatment populations. Individual decision-making during foraging may thus inform population responses to bait-based control tools. Management decisions such as prey suppression are likely to directly influence removal efficacy through altered foraging behavior in snakes.

Global Ecology and Conservatuin↗