Methylmercury declines in a boreal peatland when experimental sulfate deposition decreases

Between 2001 and 2008 we experimentally manipulated atmospheric sulfate-loading to a small boreal peatland and monitored the resulting short and long-term changes in methylmercury (MeHg) production. MeHg concentrations and %MeHg (fraction of total-Hg (Hg(T)) present as MeHg) in the porewaters of the experimental treatment reached peak values within a week of sulfate addition and then declined as the added sulfate disappeared. MeHg increased cumulatively over time in the solid-phase peat, which acted as a sink for newly produced MeHg. In 2006 a "recovery" treatment was created by discontinuing sulfate addition to a portion of the experimentally treated section to assess how MeHg production might respond to decreased sulfate loads. Four years after sulfate additions ceased, MeHg concentrations and %MeHg had declined significantly from 2006 values in porewaters and peat, but remained elevated relative to control levels. Mosquito larvae collected from each treatment at the end of the experiment exhibited Hg(T) concentrations reflective of MeHg levels in the peat and porewaters where they were collected. The proportional responses of invertebrate Hg(T) to sulfate deposition rates demonstrate that further controls on sulfur emissions may represent an additional means of mitigating Hg contamination in fish and wildlife across low-sulfur landscapes.     

Biotransformation and accumulation of arsenic in soil amended with seaweed

For many coastal regions of the world, it has been common practice to apply seaweed to the land as a soil improver and fertilizer. Seaweed is rich in arsenosugars and has a tissue concentration of arsenic up to 100 micro/g g(-1). These arsenic species are relatively nontoxic to humans; however, in the environment they may accumulate in the soil and decompose to more toxic arsenic species. The aim of this study was to determine the fate and biotransformation of these arsenosugars in soil using HPLC-ICP-MS analysis. Data from coastal soils currently manured with seaweeds were used to investigate if arsenic was accumulating in these soils. Long-term application of seaweed increased arsenic concentrations in these soils up to 10-fold (0.35 mg of As kg(-1) for nonagronomic peat, 4.3 mg of As kg(-1) for seaweed-amended peat). The biotransformation of arsenic was studied in microcosm experiments in which a sandy (machair) soil, traditionally manured with seaweed, was amended with Laminaria digitata and Fucus vesiculosus. In both seaweed species, the arsenic occurs in the form of arsenosugars (85%). The application of 50 g of seaweed to 1 kg of soil leads to an increase of arsenic in the soils, and the dominating species found in the soil pore water were dimethylarsinic acid (DMA(V)) and the inorganic species arsenate (As(V)) and arsenite (As(III)) after the initial appearance of arsenosugars. A proposed decomposition pathway of arsenosugars is discussed in which the arsenosugars are transformed to DMA(V) and further to inorganic arsenic without appreciable amounts of methylarsonic acid (MA(V)). Commercially available seaweed-based fertilizers contain arsenic concentration between 10 and 50 mg kg(-1). The arsenic species in these fertilizers depends on the manufacturing procedure. Some contain mainly arsenosugars while others contain mainly DMA(V) and inorganic arsenic. With the application rates suggested by the manufacturers, the application of these fertilizers is 2 orders of magnitude lower than the maximum permissible sewage sludge load for arsenic (varies from 0.025 kg ha(-1) yr(-1) in Styria, Austria, to 0.7 kg ha(-1) yr(-1) in the U.K.), while a direct seaweed application would exceed the maximum arsenic load by at least a factor of 2.     

Investigating arsenic speciation and mobilization in sediments with DGT and DET: a mesocosm evaluation of oxic-anoxic transitions

Mobilization of arsenic from freshwater and estuarine sediments during the transition from oxic to anoxic conditions was investigated using recently developed diffusive sampling techniques. Arsenic speciation and Fe(II) concentrations were measured at high resolution (1-3 mm) with in situ diffusive gradients in thin films (DGT) and diffusive equilibration in thin films (DET) techniques. Water column anoxia induced Fe(II) and As(III) fluxes from the sediment. A correlation between water column Fe(II) and As(III) concentrations was observed in both freshwater (r(s) = 0.896, p < 0.001) and estuarine (r(s) = 0.557, p < 0.001) mesocosms. Porewater sampling by DGT and DET techniques confirmed that arsenic mobilization was associated with the reductive dissolution of Fe(III) (hydr)oxides in the suboxic zone of the sediment; a relationship that was visible because of the ability to measure the coincident profiles of these species using combined DGT and DET samplers. The selective measurement of As(III) and total inorganic arsenic by separate DGT samplers indicated that As(III) was the primary species mobilized from the solid phase to the porewater. This measurement approach effectively ruled out substantial As(V) mobilization from the freshwater and estuarine sediments in this experiment. This study demonstrates the capabilities of the DGT and DET techniques for investigating arsenic speciation and mobilization over a range of sediment conditions.     

气相色谱法测定肉制品中甲基汞

研究肉制品中甲基汞检测方法.利用盐酸超声浸提样品后,将样品提取液用氯化钠盐析-苯萃取的方法,提取出各类食品中的甲基汞,建立了气相色谱法(附电子捕获检测器)测定食品中甲基汞的方法.本方法相对标准偏差1.31％～3.99％,检出限为0.01 mg/kg,回收率在86.4％～98.9％之间,具有操作简便快速、灵敏度高等优点.     

Methylmercury Concentrations Found in Wild and Farm-raised Paddlefish

ABSTRACT: Paddlefish ( Polyodon spathula ) were collected from 4 sites in Kentucky: the Ohio River, Lake Cumberland, and 2 aquaculture sources (private reservoir and catfish ponds). They were tested for methylmer-cury concentrations in their flesh. Paddlefish from all sources had methylmercury levels below the 1 part per million Food and Drug Administration-mandated action limit for seafood. However, using the U.S. Environmental Protection Agency reference dose for methylmercury, only paddlefish from the Ohio River exceeded the reference dose for unrestricted consumption. Some Ohio River and Lake Cumberland paddlefish had higher-than-average methylmercury concentrations, whereas aquacultured paddlefish had low concentrations of methylm-ercury. There was a direct proportionality between fish age and methylmercury concentration; older paddlefish tended to have higher amounts of methylmercury in their meat.     

高效液相色谱-原子荧光法测定水产品中甲基汞含量

建立水产品中甲基汞含量的高效液相色谱-原子荧光测定方法。样品经硫脲加氯化钾、盐酸溶液提取,提取液过固相萃取小柱净化,用流动相定容,过0.45μm微孔滤膜,采用高效液相色谱-原子荧光法检测,外标法定量。结果表明,甲基汞在2～50μg/L质量浓度范围内,色谱峰面积与甲基汞质量浓度之间线性关系良好(相关系数为0.9995),以20、200、1000μg/kg 三个添加量在空白样品中添加甲基汞,样品平均回收率为80.2%～87.1%,相对标准偏差为3.4%～6.8%,方法的定量限为20μg/kg。该方法简便快速,基体干扰小,精密度、准确性均能满足水产品中甲基汞分析。     

Methylmercury levels in predatory fish species marketed in Canada

Mercury was detected in all analysed samples of swordfish, marlin, shark and tuna purchased from major supermarket outlets and fish retailers in three cities across Canada. Total mercury and methylmercury levels ranged up to 3845 and 2346 ng g^-1, respectively. Swordfish contained the highest levels, followed by shark, fresh/frozen tuna and marlin. Levels in canned tuna were considerably less than the other examined samples. Methylmercury was extracted with toluene from enzymatically hydrolysed samples after the addition of sulphuric acid and potassium bromide. An L-cysteine back-extraction was used to separate the methylmercury from most organic co-extractives. Analysis of methylmercury (as methylmercury bromide) was by gas chromatography with pulsed discharge detection.     

Remediation of methyl iodide in aqueous solution and soils amended with thiourea

Methyl iodide (MeI) is considered a very promising fumigant alternative to methyl bromide (MeBr) for controlling soil-borne pests. Because atmospheric emission of highly volatile fumigants contributes to air pollution, feasible strategies to reduce emissions are urgently needed. In this study, thiourea (a nitrification inhibitor) was shown to accelerate the degradation of MeI in soil and water. In aqueous solution, the reaction between MeI and thiourea was independent of pH, although the rate of MeI hydrolysis increased in alkaline solution. Substantial increases in the rate of MeI dissipation were observed in thiourea-amended soils. Transformation of MeI by thiourea in aqueous solution was by a single chemical reaction process, while MeI degradation in thiourea-amended soil apparently involved a catalytic mechanism. The electron delocalization between the thiourea molecule and the surfaces of soil particles is energetically favorable and would increase the nucleophilic reactivity of the thiono group toward MeI, resulting in an enhancement of the dissipation rate. The soil half-life for MeI was reduced from >300 h for unamended soils to only a few hours in soil or sand amended with thiourea at a 2:1 molar ratio (thiourea:MeI). The MeI transformation rate in thiourea-amended soil increased with increasing soil temperature and decreasing soil moisture. Therefore, spraying thiourea on the soil surface to form a "reactive surface barrier" may be an effective and innovative strategy for controlling fumigant emissions to the atmosphere and for improving environmental protection.     

Reducing 1,3-dichloropropene emissions from soil columns amended with thiourea

Soil fumigants are becoming an important source of volatile organic compounds (VOCs) in air, especially in some agricultural areas. In this study, we used thiourea to construct a reactive surface barrier (RSB) at the soil surface for reducing 1,3-dichloropropene (1,3-D) volatilization. The agrochemical thiourea could rapidly transform volatile 1,3-D to nonvolatile products via an SN2 nucleophilic substitution reaction. A catalytic mechanism in thiourea-amended soil facilitated the conversion process. A packed soil column system was employed to investigate the emissions and distribution of 1,3-D and optimize the original fumigant emission-reduction strategy. Volatilization of 1,3-D from the soil surface was significantly reduced in columns amended with a thiourea RSB compared with that of bare soil. Volatilization flux and cumulative emissions decreased with increasing thiourea application rate and increasing fumigation depth in packed soil columns. Surface amendment with the RSB did not affect the subsurface distribution of 1,3-D in the soil profile. Combined application of a thiourea RSB and plastic tarps had a synergetic effect in emission control and could eliminate the relatively high fumigant flux that occurs upon tarp disruption. Therefore, this reduced-risk practice was very effective in reducing atmospheric emissions of VOCs from soil treatment with halogenated fumigants.     

Methylmercury in freshwater fish linked to atmospheric mercury deposition

A connection between accumulation of methylmercury (MeHg) in wild fish populations and atmospheric mercury deposition has not been made. Large databases for both MeHg in fish and atmospheric mercury deposition have been assimilated from monitoring efforts spanning the contiguous United States. Here, we compare results of these data sets and show that state-wide average concentrations of MeHg in a cosmopolitan freshwater fish, the largemouth bass Micropterus salmoides, are related positively to wet atmospheric Hg fluxes among most of the 25 states that are analyzed, which span a 5-fold range in Hg deposition. Differences in largemouth bass MeHg concentrations among states are unrelated to average precipitation depth, wet atmospheric acid deposition, or interstate variations in the type of water body (river, lake, reservoir) from which the fish were sampled. There are modest correlations between MeHg in bass and surface water pH, temperature, and wet atmospheric deposition of sulfate. However, when fish and atmospheric mercury results are combined at the state level, wet atmospheric Hg deposition accounts for about two-thirds of the variation in bass MeHg among most states, and stepwise multiple regression analysis reveals thatthese variables do not improve the linear model significantly. This suggests the accumulation of MeHg in wild fish populations is linked to atmospheric Hg loadings, two-thirds of which are estimated to be from anthropogenic sources.     

Seasonal fluctuations in zinc speciation within a contaminated wetland

The cycling of common sorbents such as metal (hydr)- oxides, carbonates, and sulfides in redox-active environments influences the partitioning of associated trace elements such as zinc. Consequently, fluctuations in redox status may in part determine the availability and mobility of Zn and other trace elements. This research examines changes in Zn speciation in a contaminated wetland soil that undergoes seasonal flooding. X-ray absorption spectroscopy (XAS) was employed to identify and quantify Zn species from soil cores collected over a 1-year cycle as a function of water depth, location, and soil depth. Zinc associated with (hydr)oxide phases in dry, oxidized soils and with sulfides and carbonates in flooded systems. An increase in water level was accompanied by a reversible change in Zn fractionation toward ZnS and ZnC03. However, a small, recalcitrant fraction of Zn associated with (hydr)oxides remained even when the soils were exposed to highly reducing conditions. Water depth and redox potential were the most important factors in determining Zn speciation, although spatial variation was also important. These data indicate that zinc sorption is a dynamic process influenced by environmental changes.     

Methylmercury in mosquitoes related to atmospheric mercury deposition and contamination

A connection between loadings of inorganic Hg, especially from the atmosphere, and accumulation of methylmercury (MeHg) in aquatic biota has not been firmly established. Mosquitoes (Diptera: Culicidae) may be a useful indictor of Hg contamination or MeHg accumulation in aquatic ecosystems because they have aquatic life stages, and their ubiquitous distribution permits sampling across wide ranges of climate, biological productivity, and atmospheric Hg deposition. We examined MeHg in adult mosquitoes from subtropical (Florida), maritime (California), continental (Michigan), and arctic (Alaska) regions of North America that span a range in wet atmospheric Hg deposition (1.5-15 microg m(-2) y(-1)). More than 90% of the Hg in mosquitoes was MeHg, and concentrations varied among locations. Levels of MeHg differed among mosquito species at six sites in northwest Florida (Ochlerotatus atlanticus < Culex nigripalpus < Anopheles crucians); this may be related to differences in biogeochemical characteristics of the aquatic habitat that affect dietary accumulation of MeHg during the larval stage. Mosquito MeHg was related positively to wet atmospheric Hg deposition among locations where atmospheric deposition is the principal source of Hg, and it was greatly enhanced in Hg-polluted environs near the Sulphur Bank Mine in Lake County, California. These results suggest that MeHg in mosquitoes may be a useful and sensitive indicator of Hg loadings to aquatic systems, including that derived from atmospheric deposition.     

Impact of redox conditions on arsenic mobilization from tailings in a wetland with neutral drainage

More than 80 years of silver mining in the Cobalt area (Ontario, Canada) has led to widespread contamination of water with arsenic. The objective of this study was to determine the impact of changes in redox conditions on the stability of As in samples collected from a tailings wetland in the historic mining camp. Dissolved metal concentrations were monitored while tailings samples (approximately 1300 mg of As kg(-1), pH 7.4) were subjected to 30 days of reduction. Reoxidation of the samples was accomplished by air drying. The As oxidation states in the original, reduced, and reoxidized samples were determined using X-ray absorption spectroscopy (XAS). Arsenic speciation was affected by changes in redox conditions, resulting in rapid mobilization of As during reduction. Glucose input had a significant impact on the dissolution and speciation of As, suggesting that the As transformation was microbially mediated. When carbon was not limiting, the combination of reducing conditions and lower pH favored the formation of As(-I) species.     

Performance of a constructed wetland with a sulfur/limestone denitrification section for wastewater nitrogen removal

The effectiveness of a nonvegetated lab-scale subsurface flow constructed wetland for wastewater treatment had been evaluated with the feed ammonium concentration of approximately 20-40 mg of NH4(+)-N L(-1) and a hydraulic retention time of approximately 10 d. The present system had a nitrification zone plus a sulfur/limestone (S/L) autotrophic denitrification zone followed by an anaerobic polishing zone and was operated with and without aeration. The wetland had only 80% organics removal and no net nitrogen removal when there was no artificial aeration. However, almost 100% organics removal and approximately 81-90% total inorganic nitrogen (TIN = NH4(+)-N + NO2(-0-N + NO3(-)-N) removal were achieved when the oxic zone of the system was aerated with compressed air. S/L autotrophic denitrification contributed 21-49% of total NO3(-)-N removal across the whole wetland and 50-95% across the S/L column. TIN and NH4(+)-N in the effluent were always < 5.5 and < 0.7 mg L(-1), respectively, when the feed had NH4(+)-N < or = 35 mg L(-1). Sulfate removal of approximately 53-69% was achieved in the anaerobic polishing zone. The position of the S/L column was changed (1.78, 2.24, and 2.69 m from the inlet), and no remarkable difference in nitrogen removal was observed. However, without the S/L column, TIN removal decreased to approximately 74%, and the effluent NO3(-)-N increased about two times (9.13 mg of N L(-1)). The present study has demonstrated the possible use of S/L autotrophic denitrification for nitrate removal in a constructed wetland.     

Positive artifact sulfate formation from SO2 adsorption in the silica gel sampler used in NIOSH Method 7903

NIOSH Method 7903, which uses one section of glass fiber filter and two sections of silica gel, has been developed to determine the total concentrations of acid mists in workplace air, although certain gases are suspected to cause interference. In this study, experiments were performed to investigate the roles of sulfur(IV) oxidation and sulfur dioxide (SO2) adsorption in causing artifacts in sulfuric acid measurement. First, sulfur(IV) oxidation, under four combinations of water bath temperature and Na2CO3 solution concentration, was examined to investigate the effect of the extraction process of NIOSH Method 7903. It was shown that sulfur(IV) oxidation to form sulfate could reach 100% within just 2-3 min, following the extraction process of NIOSH Method 7903. The results demonstrate that, using the procedure, SO2 adsorbed by the silica gel and the glass fiber filter easily yields artifact sulfate. Sulfur dioxide adsorption under various flow rates, SO2 concentrations, and sampling times was also investigated. The experimental data were fitted to a deactivation model to determine the adsorption rate constant and the deactivation rate constant. The model can serve as a tool for estimating the artifact sulfate if the SO2 concentration is available.     

Influence of pH on the formation of sulfate and hydroxyl radicals in the UV/peroxymonosulfate system

The influence of pH on the degradation of refractory organics (benzoic acid, BA) in UV(254 nm)/Peroxymonosulfate (UV/PMS) system was investigated. The degradation of BA was significantly enhanced at the pH range of 8-11, which could not be explained only by the generally accepted theory that SO(4)(?-) was converted to HO(?) at higher pH. A hypothesis was proposed that the rate of PMS photolysis into HO(?) and SO(4)(?-) increased with pH. The hypothesis was evidenced by the measured increase of apparent-molar absorption coefficient of PMS (ε(PMS), 13.8-149.5 M(-1)·cm(-1)) and photolysis rate of PMS with pH, and further proved by the increased quasi-stationary concentrations of both HO(?) and SO(4)(?-) at the pH range of 8-10. The formation of HO(?) and SO(4)(?-) in the UV/PMS system was confirmed mainly from the cooperation of the photolysis of PMS, the decay of peroxomonosulfate radical (SO(5)(?-)) and the conversion of SO(4)(?-) to HO(?) by simulation and experimental results. Additionally, the apparent quantum yield for SO(4)(?-) in the UV/PMS system was calculated as 0.52 ± 0.01 at pH 7. The conclusions above as well as the general kinetic expressions given might provide some references for the UV/PMS applications.     

Anammox bacterial abundance, biodiversity and activity in a constructed wetland

An integrated approach to document high anammox activity and biodiversity in a constructed wetland (CW) was performed and showed that substantial anammox activity could mitigate undesirable N(2)O emission. The enhanced anammox bacterial abundance, biodiversity and activity were achieved by supplementing activated sludge to the CW. Up to 3.38 × 10(7) gene copies g(-1) dry soil of anammox bacteria were enriched in the CW. The activity measured by isotope pairing technique increased from 1.6 nmol N g(-1) sludge h(-1) in the original activated sludge to 18 nmol N g(-1) soil h(-1) in the CW, with the specific cellular activity increased from 5.1 to 12.8 fmol cell(-1) d(-1). Up to 33% of produced N(2) could be attributed to anammox process in the CW, with the remainder being due to denitrification. Phylogenetic analysis of anammox bacterial 16S rRNA genes indicated a shift of community from single Candidatus "Brocadia fulgida" in sludge to multiple "Jettenia", "Brocadia", and "Anammoxoglobus" species in the CW. With static chambers and control experiments, the CW with supplemented sludge had a 30% reduced N(2)O emission flux compared with the tests without adding biomass during an 8 month testing period.     

Arsenic speciation and volatilization from flooded paddy soils amended with different organic matters

Arsenic (As) methylation and volatilization in soil can be increased after organic matter (OM) amendment, though the factors influencing this are poorly understood. Herein we investigate how amended OM influences As speciation as well as how it alters microbial processes in soil and soil solution during As volatilization. Microcosm experiments were conducted on predried and fresh As contaminated paddy soils to investigate microbial mediated As speciation and volatilization under different OM amendment conditions. These experiments indicated that the microbes attached to OM did not significantly influence As volatilization. The arsine flux from the treatment amended with 10% clover (clover-amended treatment, CT) and dried distillers grain (DDG) (DDG-amended treatment, DT2) were significantly higher than the control. Trimethylarsine (TMAs) was the dominant species in arsine derived from CT, whereas the primary arsine species from DT2 was TMAs and arsine (AsH(3)), followed by monomethylarsine (MeAsH(2)). The predominant As species in the soil solutions of CT and DT2 were dimethylarsinic acid (DMAA) and As(V), respectively. OM addition increased the activities of arsenite-oxidizing bacteria (harboring aroA-like genes), though they did not increase or even decrease the abundance of arsenite oxidizers. In contrast, the abundance of arsenate reducers (carrying the arsC gene) was increased by OM amendment; however, significant enhancement of activity of arsenate reducers was observed only in CT. Our results demonstrate that OM addition significantly increased As methylation and volatilization from the investigated paddy soil. The physiologically active bacteria capable of oxidization, reduction, and methylation of As coexisted and mediated the As speciation in soil and soil solution.