Mass-Dependent and -Independent Fractionation of Hg Isotopes by Photoreduction in Aquatic Systems

Mercury (Hg) isotopes can be used as tracers of Hg biogeochemical pathways in the environment. The photochemical reduction of aqueous Hg species by natural sunlight leads to both mass-dependent fractionation (MDF) of Hg isotopes and mass-independent fractionation (MIF) of the odd-mass isotopes, with the relation between the MIF for the two odd isotopes being distinct for different photoreduction pathways. Large variations in MDF and MIF are observed in fish and provide new insights into the sources and bioaccumulation of Hg in food webs. MIF in fish can also be used to estimate the loss of methylmercury via photoreduction in aquatic ecosystems.

Inactivation of glutathione peroxidase by superoxide radical

The selenium-containing glutathione peroxidase, when in its active reduced form, was inactivated during exposure to the xanthine oxidase reaction. Superoxide dismutase completely prevented this inactivation, whereas catalase, hydroxyl radical scavengers, or chelators did not, indicating that O2 was the responsible agent. Conversion of GSH peroxidase to its oxidized form, by exposure to hydroperoxides, rendered it insensitive toward O2. The oxidized enzyme regained susceptibility toward inactivation by O2 when reduced with GSH. The inactivation by O2 could be reversed by GSH; however, sequential exposure to O2 and then hydroperoxides caused irreversible inactivation. Reactivity toward CN- has been used as a measure of the oxidized form of GSH peroxidase, whereas reactivity toward iodoacetate has been taken as an indicator of the reduced form. By these criteria both O2 and hydroperoxides convert the reduced form to oxidized forms. A mechanism involving oxidation of the selenocysteine residue at the active site has been proposed to account for these observations.

Reporting of variations in the natural isotopic composition of mercury

High-precision measurements of natural variations in the stable isotopic composition of mercury show great promise as a new tracer of mercury sources and chemical transformations in the environment. We strongly suggest that all laboratories adopt a common means of data correction, standardization, and nomenclature in order to ensure that data from various laboratories can be easily evaluated and compared. We make suggestions for mass bias correction, reporting of mass-dependent and mass-independent isotope variations, and a standard protocol for reporting analytical uncertainties. We also present our measured values for isotope ratios in several mercury standard solutions.

Algal blooms reduce the uptake of toxic methylmercury in freshwater food webs

Mercury accumulation in fish is a global public health concern, because fish are the primary source of toxic methylmercury to humans. Fish from all lakes do not pose the same level of risk to consumers. One of the most intriguing patterns is that potentially dangerous mercury concentrations can be found in fish from clear, oligotrophic lakes whereas fish from greener, eutrophic lakes often carry less mercury. In this study, we experimentally tested the hypothesis that increasing algal biomass reduces mercury accumulation at higher trophic levels through the dilution of mercury in consumed algal cells. Under bloom dilution, as algal biomass increases, the concentration of mercury per cell decreases, resulting in a lower dietary input to grazers and reduced bioaccumulation in algal-rich eutrophic systems. To test this hypothesis, we added enriched stable isotopes of Hg to experimental mesocosms and measured the uptake of toxic methylmercury (CH3 200Hg+) and inorganic 201Hg2+ by biota at several algal concentrations. We reduced absolute spike detection limits by 50-100 times compared with previous techniques, which allowed us to conduct experiments at the extremely low aqueous Hg concentrations that are typical of natural systems. We found that increasing algae reduced CH3Hg+ concentrations in zooplankton 2-3-fold. Bloom dilution may provide a mechanistic explanation for lower CH3Hg+ accumulation by zooplankton and fish in algal-rich relative to algal-poor systems.

Randomized, open-label, phase II trial of oral capecitabine (Xeloda) vs. a reference arm of intravenous CMF (cyclophosphamide, methotrexate and 5-fluorouracil) as first-line therapy for advanced/metastatic breast cancer

BACKGROUND

Oral capecitabine was evaluated in terms of overall response rate, safety, and tolerability as first-line therapy in women aged > or = 55 years with advanced/metastatic breast cancer.

PATIENTS AND METHODS

Ninety-five patients were randomized (2:1) to either intermittent oral capecitabine 1,255 mg/m2 twice daily (two weeks' treatment followed by a one-week rest period) or intravenous CMF (cyclophosphamide. methotrexate, 5-fluorouracil [5-FU]) administered every three weeks.

RESULTS

The overall response rate in the capecitabine group was 30% (95% confidence interval (95% CI): 19%-43%), including three complete responses (5%). The response rate observed in the CMF group was 16% (95% CI: 5%-33%), with no complete responses. Median time to disease progression was 4.1 months with capecitabine and 3.0 months with CME. Survival was similar in the two treatment groups (median 19.6 months with capecitabine. 17.2 months with CMF). The safety profiles were different for capecitabine and CMF. However, both regimens were generally well tolerated and treatment interruption and/or dose modification was effective in managing toxicities associated with capecitabine. Alopecia and myelosuppression were rare in patients receiving capecitabine while diarrhea and hand-foot syndrome were more common. Treatment interruption and/or individual dose adjustment of capecitabine was required in 34% of patients and was generally effective in managing adverse events. Treatment was stopped owing to toxicity in 16% of patients in the capecitabine arm. The incidence of deaths during or within 28 days of stopping study treatment was 8% and 6% in the capecitabine and CMF arms, respectively.

CONCLUSIONS

An oral, twice-daily regimen of capecitabine is effective and well tolerated when used as first-line chemotherapy in older patients (> or = 55 years) with advanced/metastatic breast cancer, and is suitable for outpatient therapy.

The utility of transbronchial needle aspiration in the staging of bronchogenic carcinoma

We conducted a prospective multi-institutional clinical study involving community hospitals and academic medical centers to more carefully define the value of computerized tomography (CT) of the chest with transbronchial needle aspiration (TBNA) in the staging of bronchogenic carcinoma (CA), and to assess the predictors of a positive aspirate. Of 360 individuals determined to have bronchogenic carcinoma, 50 of 81 (62%) with small cell carcinoma (SCC) and 135 of 279 (48%) with non-small cell carcinoma (NSCC) had positive aspirates (p = 0.034). TBNA precluded additional thoracic surgery in a total of 104 of 360 (29%) patients and was exclusively diagnostic of carcinoma in 65 of 360 (18%) cases. Right-sided tumors were more likely to have a positive mediastinal TBNA (p = 0.002 to 0. 01) as were histologic (67 of 118 [57%]) rather than cytology aspirates (228 of 532 [41%]) (p < 0.001). Sensitivity was > 57% in lymph nodes (LN) >/= 10 mm, and among LN of equivalent size, right paratracheal and subcarinal sites were most likely to establish malignancy. Preoperative CT is a valuable adjunct in the staging of CA by TBNA. Increasing LN size, right-sided tumors, right paratracheal and subcarinal locations, use of a histology needle, and the presence of SCC are the best predictors of a positive aspirate.

Treatment of cutaneous leishmaniasis among travellers

Leishmaniasis is endemic in 88 countries on five continents. There are 1-1.5 million cases of cutaneous leishmaniasis reported yearly worldwide. There has been a sharp increase in recorded cases over the last 10 years. Based on geographical distribution, cutaneous leishmaniasis is divided into Old World and New World leishmaniasis. In the past, species could be inferred from geographical setting or determined by performing culture and isoenzyme analysis. The recently developed and now widely available PCR technology allows a rapid diagnosis with determination of most species, and thus enables a species-orientated treatment. While the Old World species mostly cause benign and often self-limiting cutaneous disease, the American species cause a broad spectrum of conditions from benign to severe manifestations, including mucosal involvement. The response to treatment varies according to the species. Therefore, a species-specific approach is proposed. Drugs for systemic and topical treatment are presented and discussed with regard to their application, use and adverse effects. Indications for local or systemic treatment are proposed. Drugs under investigation are also mentioned. An overview of published treatment options and a treatment recommendation is given for each of the most important species. The level of evidence of the studies leading to these recommendations is given.

Isotopic composition and fractionation of mercury in Great Lakes precipitation and ambient air

Atmospheric deposition is a primary pathway by which mercury (Hg) enters terrestrial and aquatic ecosystems; however, the chemical and meteorological processes that Hg undergoes from emission to deposition are not well understood. Hg stable isotope geochemistry is a growing field used to better understand Hg biogeochemical cycling. To examine the atmospheric Hg isotopic composition in the Great Lakes, precipitation and ambient vapor-phase Hg samples were collected in Chicago, IL, Holland, MI, and Dexter, MI, between April 2007 and September 2009. Precipitation samples were characterized by negative mass-dependent fractionation (MDF) (δ(202)Hg = -0.79‰ to 0.18‰), while most vapor-phase samples displayed positive MDF (δ(202)Hg = -0.59‰ to 0.43‰). Positive mass-independent fractionation (MIF) (Δ(199)Hg = 0.04‰ to 0.52‰) was observed in precipitation, whereas MIF was slightly negative in vapor-phase samples (Δ(199)Hg = -0.21‰ to 0.06‰). Significant positive MIF of (200)Hg up to 0.25‰ was also measured in precipitation. Such MIF of an even-mass Hg isotope has not been previously reported in natural samples. These results contrast with recent predictions of the isotopic composition of atmospheric Hg and suggest that, in addition to aqueous photoreduction, other atmospheric redox reactions and source-related processes may contribute to isotopic fractionation of atmospheric Hg.

Stable isotope (N, C, Hg) study of methylmercury sources and trophic transfer in the northern gulf of Mexico

We combined N, C, and Hg stable isotope measurements to identify the most important factors that influence MeHg accumulation in fish from the northern Gulf of Mexico (nGOM), and to determine if coastal species residing in the Mississippi River (MR) plume and migratory oceanic species derive their MeHg from the same, or different, sources. In six coastal species and two oceanic species (blackfin and yellowfin tuna), trophic position as measured by delta(15)N explained most of the variance in log[MeHg] (r(2) approximately 0.8), but coastal species and tuna fell along distinct, nearly parallel lines with significantly different intercepts. The tuna also had significantly higher delta(202)Hg (0.2-0.5 per thousand) and Delta(201)Hg ( approximately 1.5 per thousand) than the coastal fish (delta(202)Hg = 0 to -1.0 per thousand; Delta(201)Hg approximately 0.4 per thousand). The observations can be best explained by largely disconnected food webs rooted in different baseline delta(15)N signatures (MR-plume vs oceanic) and isotopically distinct MeHg sources, with oceanic MeHg having undergone substantial photodegradation ( approximately 50%) before entering the base of the food web. Given the MR's large, productive footprint in the nGOM and the potential for exporting prey and MeHg to the adjacent oligotrophic GOM, the disconnected food webs and different MeHg sources are consistent with recent evidence in other systems of important oceanic MeHg sources.

Tissue engineering scaffolds using superstructures

Here, scaffolds as cell and tissue carriers are approached from an engineering point of view, emphasizing material superstructuring in the design of supports. Superstructure engineering provides optimal spatial and nutritional conditions for cell maintenance by the arrangement of structural elements (e.g. pores or fibres) so as to vary the order of cell to cell contact. This approach is illustrated in the design of several scaffolds: knitted fabrics as three-dimensional superstructures for optimized osteosynthesis implants, a new injectable open porous implant system, an angiopolar non-degradable ceramic cell carrier, and an injectable or microsurgically implantable entangled carrier system. The implications for tissue engineering are discussed.

Measurement of low levels of arsenic exposure: a comparison of water and toenail concentrations

A study was conducted to evaluate toenail arsenic concentrations as a biologic marker of drinking water arsenic exposure. Study subjects were controls in a US population-based case-control study of nonmelanoma skin cancer, randomly selected from drivers' license records (those < 65 years of age) and Medicare enrollment files (those > or = 65 years of age). Between 1994 and 1997, a total of 540 controls were interviewed and toenail samples of sufficient weight were collected from 506 (93.7%) of these. Beginning in 1995, a sample of tap water was taken from the participants' homes; a total of 217 (98.6%) water samples were obtained from the 220 subjects interviewed. Arsenic determinations were made from toenail samples using neutron activation analysis. Water samples were analyzed using hydride-generation magnet sector inductively coupled mass spectrometry. Among 208 subjects with both toenail and water measurements, the correlation (r) between water and nail arsenic was 0.65 (p < 0.001) among those with water arsenic concentrations of 1 microg/liter or higher and 0.08 (p = 0.31) among those with concentrations below 1 microg/liter (overall r = 0.46, p < 0.001). Our data suggest that toenail samples provide a useful biologic marker for quantifying low-level arsenic exposure.

A multicenter trial with a somatostatin analog (99m)Tc depreotide in the evaluation of solitary pulmonary nodules

OBJECTIVE

The affinity of various malignant neoplasms including small cell and non-small cell lung cancer for peptide analogs of somatostatin has been well documented. Depreotide is such an analog and can be complexed with technetium-99m ((99m)Tc depreotide) for optimal imaging properties. Using this radiopharmaceutical, solitary pulmonary nodules (SPN) were previously evaluated in a successful phase II/III trial. The results of the larger multicenter phase III study using (99m)Tc depreotide to differentiate malignant and benign etiologies in SPN are now presented.

METHODS

Patients with SPN </= 6 cm on chest radiograph were referred for evaluation. One hundred fourteen individuals who had an absence of a benign pattern of calcification on CT scan, age > 30 years, and no demonstrable radiographic stability for the prior 2 years were studied. All underwent single-photon emission CT (SPECT) with (99m)Tc depreotide and subsequent tissue histologic examination. Three nuclear medicine specialists blinded to histologic findings examined the SPECT images and scored them as positive or negative based on the presence or absence of activity in the radiographic region of the SPN. The final result was determined by the majority score, which was then compared with the histologic result.

RESULTS

Of the 114 individuals studied, 88 had a histologic result compatible with malignant neoplasm. (99m)Tc depreotide scintigraphy correctly identified 85 of this group, with three false-negative determinations compared with histology. There were seven false-positive determinations, including six granulomas and one hamartoma. (99m)Tc depreotide scintigraphy correctly excluded malignancy in 19 of 26 patients with benign histologic findings. The sensitivity of this method was 96.6% with a specificity of 73.1%.

CONCLUSION

(99m)Tc depreotide scintigraphy is a safe and useful method for the noninvasive evaluation of SPN with a sensitivity and accuracy comparable to that reported for fluorine-18 fluorodeoxyglucose positron emission tomography.

Mercury stable isotope fractionation during reduction of Hg(II) to Hg(0) by mercury resistant microorganisms

Mercury (Hg) undergoes systematic stable isotopic fractionation; therefore, isotopic signatures of Hg may provide a new tool to track sources, sinks, and dominant chemical transformation pathways of Hg in the environment. We investigated the isotopic fractionation of Hg by Hg(II) resistant (HgR) bacteria expressing the mercuric reductase (MerA) enzyme. The isotopic composition of both the reactant Hg(II) added to the growth medium and volatilized product (Hg(0)) was measured using cold vapor generation and multiple collector inductively coupled plasma mass spectrometry. We found that exponentially dividing pure cultures of a gram negative strain Escherichia coli JM109/pPB117 grown with abundant electron donor and high Hg(II) concentrations at 37, 30, and 22 degrees C, and a natural microbial consortium incubated in natural site water at 30 degrees C after enrichment of HgR microbes, preferentially reduced the lighter isotopes of Hg. In all cases, Hg underwent Rayleigh fractionation with the best estimates of alpha202/198 values ranging from 1.0013 to 1.0020. In the cultures grown at 37 degrees C, below a certain threshold Hg(II) concentration, the extent of fractionation decreased progressively. This study demonstrates mass-dependent kinetic fractionation of Hg and could lead to development of a new stable isotopic approach to the study of Hg biogeochemical cycling in the environment.

MRI of bone marrow edema-like signal in the pathogenesis of subchondral cysts

OBJECTIVE

To determine if a relationship exists between bone marrow edema-like signal and subchondral cysts on magnetic resonance imaging (MRI).

DESIGN

Retrospective cohort of 32 patients with two sequential knee MRI. Patients with acute trauma, infection, neoplasm, or osteonecrosis were excluded. The degree of osteoarthritis was assessed using an adaptation of the Baltimore Longitudinal Study of Aging (BLSA) scale. Initial and follow-up exams were reviewed for presence, location, size and changes of marrow edema-like signal, subarticular cysts and cartilage abnormality. All locations in the knee were aggregated for analysis with descriptive statistics.

RESULTS

The mean time interval between exams was 17.52 months (range 2.1-40.1 months). There were 23 cysts: 11 (47.8%) new, 6 (26.1%) increased size, 1 (4.4%) decreased size, and 5 (21.7%) no change in pre-existing lesions. Cysts always arose from regions of marrow edema-like signal. There were 68 subarticular areas of marrow edema-like signal: 16 (23.5%) new, 23 (33.8%) increased size, 17 (25%) decreased size, 11 (16.2%) resolved and 1 (1.5%) no change in pre-existing lesion. Marrow edema-like signal size always changed with cyst development: increased in 6/11 (54.5%), decreased in 2/11 (18.1%) and resolved in 3/11 (27.2%). Change in cyst size was always accompanied by a change in edema-like signal size. An MRI visible cartilage abnormality was adjacent to 87% (20/23) of cysts. The mean BLSA score changed from 2.6 to 3.6 indicating an overall progression of osteoarthritis.

CONCLUSION

Subchondral cysts develop in pre-existing regions of subchondral bone marrow edema-like signal.

Administration of misoprostol by trained traditional birth attendants to prevent postpartum haemorrhage in homebirths in Pakistan: a randomised placebo-controlled trial

Objective

To determine if misoprostol is safe and efficacious in preventing postpartum haemorrhage (PPH) when administered by trained traditional birth attendants (TBA) at home deliveries.

Design

A randomised, double-blind, placebo-controlled trial.

Setting

Chitral, Khyber Pakhtunkhwa Province, Pakistan.

Population

A total of 1119 women giving birth at home.

Methods

From June 2006 to June 2008, consenting women were randomised to receive 600 μg oral misoprostol (n = 534) or placebo (n = 585) after delivery to determine whether misoprostol reduced the incidence of PPH (≥500 ml).

Main outcome measures

The primary outcomes were measured blood loss ≥500 ml after delivery and drop in haemoglobin >2 g/dl from before to after delivery.

Results

Oral misoprostol was associated with a significant reduction in the rate of PPH (≥500 ml) (16.5 versus 21.9%; relative risk 0.76, 95% CI 0.59–0.97). There were no measurable differences between study groups for drop in haemoglobin >2 g/dl (relative risk 0.79, 95% CI 0.62–1.02); but significantly fewer women receiving misoprostol had a drop in haemoglobin >3 g/dl, compared with placebo (5.1 versus 9.6%; relative risk 0.53, 95% CI 0.34–0.83). Shivering and chills were significantly more common with misoprostol. There were no maternal deaths among participants.

Conclusions

Postpartum administration of 600 μg oral misoprostol by trained TBAs at home deliveries reduces the rate of PPH by 24%. Given its ease of use and low cost, misoprostol could reduce the burden of PPH in community settings where universal oxytocin prophylaxis is not feasible. Continual training and skill-building for TBAs, along with monitoring and evaluation of programme effectiveness, should accompany any widespread introduction of this drug.

Trial registration

http://clinicaltrials.gov/NCT00120237 Misoprostol for the Prevention of Postpartum Hemorrhage in Rural Pakistan.

Design of an epidemiologic study of drinking water arsenic exposure and skin and bladder cancer risk in a U.S. population

Ingestion of arsenic-contaminated drinking water is associated with an increased risk of several cancers, including skin and bladder malignancies; but it is not yet clear whether such adverse effects are present at levels to which the U.S. population is exposed. In New Hampshire, detectable levels of arsenic have been reported in drinking water supplies throughout the state. Therefore, we have begun a population-based epidemiologic case-control study in which residents of New Hampshire diagnosed with primary squamous cell (n = 900) and basal cell (n = 1200) skin cancers are being selected from a special statewide skin cancer incidence survey; patients diagnosed with primary bladder cancers (n = 450) are being identified through the New Hampshire State Cancer Registry. Exposure histories of these patients will be compared to a control group of individuals randomly selected from population lists (n = 1200). Along with a detailed personal interview, arsenic and other trace elements are being measured in toenail clipping samples using instrumental neutron activation analysis. Household water samples are being tested on selected participants using a hydride generation technique with high-resolution inductively coupled plasma mass spectrometry. In the first 793 households tested arsenic concentrations ranged from undetectable (0.01 microgram/l) to 180 microgram/l. Over 10% of the private wells contained levels above 10 microgram/l and 2.5% were above 50 microgram/l. Based on our projected sample size, we expect at least 80% power to detect a 2-fold risk of basal cell or squamous cell skin cancer or bladder cancer among individuals with the highest 5% toenail concentrations of arsenic.

Investigation of local mercury deposition from a coal-fired power plant using mercury isotopes

Coal combustion accounts for approximately two-thirds of global anthropogenic mercury (Hg) emissions. Enhanced deposition of Hg can occur close to coal-fired utility boilers (CFUBs), but it is difficult to link specific point sources with local deposition. Measurement of Hg stable isotope ratios in precipitation holds promise as a tool to assist in the identification of local Hg deposition related to anthropogenic emissions. We collected daily event precipitation samples in close proximity to a large CFUB in Crystal River, Florida. Precipitation samples collected in Crystal River were isotopically distinct and displayed large negative δ(202)Hg values (mean = -2.56‰, 1 SD = 1.10‰, n = 28). In contrast, precipitation samples collected at other sites in FL that were not greatly impacted by local coal combustion were characterized by δ(202)Hg values close to 0‰ (mean = 0.07‰, 1 SD = 0.17‰, n = 13). These results indicate that, depending on factors such as powdered coal isotopic composition and efficiency of Hg removal from flue gas, Hg deposited near CFUBs can be isotopically distinct. As this tool is further refined through future studies, Hg stable isotopes may eventually be used to quantify local deposition of Hg emitted by large CFUBs.

Efficacy of new, concise schedule for melarsoprol in treatment of sleeping sickness caused by Trypanosoma brucei gambiense: a randomised trial

BACKGROUND

African trypanosomiasis is a fatal disease caused by protozoan parasites of the species Trypanosoma brucei. The disease has reached epidemic dimensions in various countries of central Africa. Treatment of the second stage is long and complicated, and is hampered by severe adverse reactions to the first-line drug, melarsoprol. Despite these problems, melarsoprol is likely to remain the drug of choice for the next decade. We therefore did a randomised trial comparing the standard treatment schedule with a new, concise regimen.

METHODS

The safety and efficacy of the new schedule were assessed in patients presenting to a hospital in Kwanza Norte, Angola with sleeping sickness. The control group followed the 26-day standard Angolan schedule of three series of four daily injections of melarsoprol at doses increasing from 1.2 to 3.6 mg/kg within each series, with a 7-day interval between series. The new treatment schedule comprised 10 daily injections of 2.2 mg/kg. Primary outcomes assessed were elimination of parasites, deaths attributed to treatment, and rate of encephalopathy. Analysis was by intention to treat.

FINDINGS

Of 767 patients with second-stage disease, 500 were enrolled: 250 were assigned the standard schedule, and 250 the new schedule. 40 patients on the standard schedule and 47 on the new schedule had adverse events which resulted in treatment disruption or withdrawal. 50 patients on the standard regimen deviated or withdrew from treatment, compared with two on the new regimen. Parasitological cure 24 h after treatment was 100% in both groups; there were six deaths (all due to encephalopathy) 30 days after treatment in each group. The number of patients with encephalopathic syndromes was also the same in each group (14). Skin reactions were more common with the new treatment, but all could be resolved by additional medication or withdrawal of treatment.

INTERPRETATION

Considering the economic and practical advantages of the new 10-day schedule over the standard 26-day treatment schedule, and the similarity of treatment outcome, the new schedule is a useful alternative to the present standard, especially in epidemic situations and in locations with limited resources.

Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity

We performed two controlled experiments to determine the amount of mass-dependent and mass-independent fractionation (MDF and MIF) of methylmercury (MeHg) during trophic transfer into fish. In experiment 1, juvenile yellow perch (Perca flavescens) were raised in captivity on commercial food pellets and then their diet was either maintained on unamended food pellets (0.1 μg/g MeHg) or was switched to food pellets with 1.0 μg/g or 4.0 μg/g of added MeHg, for a period of 2 months. The difference in δ(202)Hg (MDF) and Δ(199)Hg (MIF) between fish tissues and food pellets with added MeHg was within the analytical uncertainty (δ(202)Hg, 0.07 ‰; Δ(199)Hg, 0.06 ‰), indicating no isotope fractionation. In experiment 2, lake trout (Salvelinus namaycush) were raised in captivity on food pellets and then shifted to a diet of bloater (Coregonus hoyi) for 6 months. The δ(202)Hg and Δ(199)Hg of the lake trout equaled the isotopic composition of the bloater after 6 months, reflecting reequilibration of the Hg isotopic composition of the fish to new food sources and a lack of isotope fractionation during trophic transfer. We suggest that the stable Hg isotope ratios in fish can be used to trace environmental sources of Hg in aquatic ecosystems.

Natural mercury isotope variation in coal deposits and organic soils

There is a need to distinguish among sources of Hg to the atmosphere in order to more fully understand global Hg pollution. In this study we investigate whether coal deposits within the United States, China, and Russia-Kazakhstan, which are three of the five greatest coal-producing regions, have diagnostic Hg isotopic fingerprints that can be used to discriminate among Hg sources. We also investigate the Hg isotopic composition of modern organic soil horizons developed in areas distant from point sources of Hg in North America. Mercury stored in coal deposits displays a wide range of both mass dependent fractionation (MDF, delta202Hg) and mass independent fractionation (MIF, delta201Hg). delta202Hg varies in coals by 3 per thousand and delta201Hg varies by 0.9 per thousand. Combining these two Hg isotope signals results in what may be a unique isotopic "fingerprint" for many coal deposits. Mass independent fractionation of mercury has been demonstrated to occur during photochemical reactions of mercury. This suggests that Hg found in most coal deposits was subjected to photochemical reduction near the Earth's surface prior to deposition. The similarity in MDF and MIF of modern organic soils and coals from North America suggests that Hg deposition from coal may have imprinted an isotopic signature on soils. This research offers a new tool for characterizing mercury inputs from natural and anthropogenic sources to the atmosphere and provides new insights into the geochemistry of mercury in coal and soils.

Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments

Identification of sources of biologically accessible Hg is necessary to fully evaluate Hg exposure in aquatic ecosystems. This study assesses the relationship between Hg in forage fish and Hg in surface sediments throughout San Francisco Bay (SF Bay) and evaluates processes influencing the incorporation of Hg into the aquatic food web. We measured the Hg stable isotope compositions of two nearshore fish species and compared them with previously reported analyses of colocated intertidal surface sediments. Fish δ(202)Hg values (mass-dependent fractionation) demonstrated a distinct spatial gradient within SF Bay that ranged from 0.60‰ in the south to -0.25‰ in the north. Fish δ(202)Hg values were consistently higher than sediment δ(202)Hg values by 0.73‰ (±0.16‰, 1SD). Fish and sediment δ(202)Hg values in SF Bay proper were well correlated (r(2) = 0.83), suggesting that sediment is a primary source of Hg to the nearshore aquatic food web. Fish Δ(199)Hg values (mass-independent fractionation) ranged from 0.46‰ to 1.55‰, did not correlate with sediment values, and yielded a Δ(199)Hg/Δ(201)Hg ratio of 1.26 (±0.01, 1SD; r(2) = 0.99). This mass-independent fractionation is consistent with photodegradation of MeHg to varying degrees at each site prior to incorporation into the food web.

Sorption of mercuric ion by synthetic nanocrystalline mackinawite (FeS)

Iron sulfides are known to be efficient scavengers of heavy metals. In this study, Hg(II) sorption was investigated using synthetic nanocrystalline mackinawite (a disordered phase) as a function of initial Hg(II) concentration [Hg(II)]0, initial FeS concentration [FeS]0, total chloride concentration CIT, and pH. Hg(II) sorption mechanisms are dependent on relative concentrations of [Hg(II)]0 and [FeS]0 (the molar ratio of [Hg(II)0/[FeS]0). When the molar ratio of [Hg(II)]0/[FeS]o is as low as 0.05, adsorption is mainly responsible for Hg(II) removal, with its contribution to the overall sorption increasing at lower Cl(T). As the molar ratio increases, the adsorption capacity becomes saturated, resulting in precipitation of a sparingly soluble HgS(s). XRD analysis indicates formation of metacinnabar (beta-HgS). Concurrently with HgS(s) precipitation, the released Fe(II) from FeS(s) is resorbed by adsorption at acidic pH and either adsorption or precipitation as Fe (hydr)-oxides at neutral to basic pH. Subsequently, the Fe precipitate formed at neutral to basic pH serves as an adsorbent for Hg(II). Under the conditions where either adsorption or HgS(s) precipitation is dominant, more than 99% of [Hg(II)]0 is immobilized. When the molar ratio of [Hg(II)]0/[FeS]0 exceeds 1, the sulfide concentration is no longer sufficient for HgS(s) precipitation, and formation of chloride salts (Hg2Cl2 at acidic pH and HgCl2 x 3HgO at basic pH) occurs.