Trace Metal Concentrations in Marsh Profiles Under the Influence of an Emerging Delta (Atchafalaya River and Wax Lake Delta) Overlying a Several Thousand Year Old (Former)Mississippi River Delta Lobe

There are concerns over the increasing concentrations of trace metals being found in the environment. Deltas are essentially integrators of watershed contamination as they are the repositories of sediment transported from and through the watershed. In order to assess changes in trace metal concentrations transported by the Mississippi River–Atchafalaya River systems, vibracores were collected from three coastal freshwater marsh sites under the influence of the Atchafalaya River and emerging Wax Lake Delta (WLD). The cores extended to a depth of 4 m which included deposits of an earlier Mississippi River Delta lobe. C-14 dating showed an age at the lower depth corresponding to approximately 3500 years ago. Vertical profile distribution of metals and metalloids were measured and comparisons between older deposits and concentrations in recent deposits were made. Concentrations of As, Cr, Cu, Ni, Zn, Mo, V, Co, and Hg metals were measured in the profiles along with Fe, Mn, and Al. There was no significant increase in heavy metals or metalloids in recent years as compared to more than 3000-year-old sediment associated with an earlier Mississippi River Delta lobe. Results show that sediment diversion through the Wax Lake Outlet did not increase concentrations of these metals in surface marsh soils. The metal concentrations in the marsh profile were compared to ERL (effects range low) and ERM (effects range medium) values to allow an ecotoxicological assessment. Arsenic was below the ERM values but was greater than the ERL which indicate a potential toxicity under certain conditions. All other metal/metalloids measured were below ERL limits. This study suggests that planned Mississippi River sediment diversions designed to slow the rate of coastal land loss are not likely to lead to trace metals contamination.     

Regional distribution characteristics and ecological risk assessment of heavy metal pollution of different land use in an antimony mining area – Xikuangshan,China

Abstract

Mining activities have introduced various heavy metals and metalloids to surrounding soil environments, causing adverse impacts to the ecological environment system. The extremely high concentration of various heavy metals and metalloids make the Xikuangshan (Hunan, China) an excellent model to assess their ecological risk. In this study, the soil samples from 26 locations of different land use methods in four areas (smelting area, road nearby ore, mining area, and ore tailing area) in Xikuangshan with different levels of various heavy metals and metalloids (Sb, As, Pb, and Cd) were analyzed; in addition, the index of geo-accumulation and the potential ecological risk index were used to evaluate ecological risk. The results showed that the average contents of Sb, As, Pb, and Cd in all soil samples were 4368.222?mg·kg^?1, 40.722?mg·kg^?1, 248.013?mg·kg^?1, and 40.941?mg·kg^?1, respectively, implying serious contamination of compound pollution of heavy metals in soil. The concentration of heavy metals in soil among smelting area, road nearby ore, mining area, and ore tailing area showed significant distribution characteristics of region because different mining activities such as smelting, mining, transportation, and stacking caused different pollution intensity. Moreover, the contents of Sb in soil samples decreased successively in residue field, wasteland, forestland, sediment, grassland, and vegetable field, and the contents of Sb in vegetable-field and ecological restoration grassland were relatively low, which indicate that the method of grassland ecological restoration is an effective method to control antimony pollution in soil. The results of ecological risk assessment showed that the antimony mining area was seriously polluted by Sb, As, Pb, and Cd, and had strong ecological risk, and Sb and Cd were the most important pollution factors, which indicated that the pollution of Sb and Cd should be a major concern of relevant departments of environment and health.     

Characterization of Chemical Contamination in Shallow-Water Estuarine Habitats of an Industrialized River. Part II. Metals

The lower six miles of the tidal portion of the Passaic River (Study Area) has long been heavily industrialized. The objectives of this study were to: quantify the present extent and magnitude of metals contamination in surface sediments in the Study Area, evaluate the contamination in the Study Area relative to a reference area and surrounding regional waterways, assess the potential for adverse effects to aquatic organisms, and identify spatial gradients in concentrations that may indicate potential point-sources of metals. We also examined the role of natural sediment characteristics in metals concentration variability. Study Area sediments were generally enriched in barium, cadmium, chromium, copper, lead, manganese, mercury, silver, selenium, and zinc relative to the reference area. Compared to available sediment quality benchmarks, the only metals in the Study Area presently at average concentrations sufficiently high to warrant concern about potential aquatic toxicity are lead, mercury, and zinc. Compared to the rest of the NY/NJ Harbor Estuary, the Study Area generally contains elevated levels of lead, manganese, silver, and zinc. Variability in metals concentrations can not be accounted for by TOC or percent fines. However, a substantial proportion of the spatial variability in a number of metals can be explained by normalization to either aluminum or iron.     

Uptake and transformation of metals and metalloids by microbial mats and their use in bioremediation

Summary Constructed microbial mats, used for studies on the removal and transformation of metals and metalloids, are made by combining cyanobacteria inoculum with a sediment inoculum from a metal-contaminated site. These mats are a heterotrophic and autotrophic community dominated by cyanobacteria and held together by slimy secretions produced by various microbial groups. When contaminated water containing high concentrations of metals is passed over microbial mats immobilized on glass wool, there is rapid removal of the metals from the water. The mats are tolerant of high concentrations of toxic metals and metalloids, such as cadmium, lead, chromium, selenium and arsenic (up to 350 mg L^–1). This tolerance may be due to a number of mechanisms at the molecular, cellular and community levels. Management of toxic metals by the mats is related to deposition of metal compounds outside the cell surfaces as well as chemical modification of the aqueous environment surrounding the mats. The location of metal deposition is determined by factors such as redox gradients, cell surface micro-environments and secretion of extra-cellular bioflocculents. Metal-binding flocculents (polyanionic polysaccharides) are produced in large quantities by the cyanobacterial component of the mat. Steep gradients of redox and oxygen exist from the surface through the laminated strata of microbes. These are produced by photosynthetic oxygen production at the surface and heterotrophic consumption in the deeper regions. Additionally, sulfur-reducing bacteria colonize the lower strata, removing and utilizing the reducing H₂S, rather than water, for photosynthesis. Thus, depending on the chemical character of the microzone of the mat, the sequestered metals or metalloids can be oxidized, reduced and precipitated as sulfides or oxides. For example precipitates of red amorphous elemental selenium were identified in mats exposed to selenate (Se-VI) and insoluble precipitates of manganese, chromium, cadmium, cobalt, and lead were found in mats exposed to soluble salts of these metals. Constructed microbial mats offer several advantages for use in the bioremediation of metal-contaminated sites. These include low cost, durability, ability to function in both fresh and salt water, tolerance to high concentrations of metals and metalloids and the unique capacity of mats to form associations with new microbial species. Thus one or several desired microbial species might be integrated into mats in order to design the community for specific bioremediation applications.     

Experimental Study of Mobility and Kinetic Characterization of Trace Elements in Contaminated Sediments from a River Basin in Northern Peru

In the Jequetepeque basin (Peru), gold extraction activity has been performed in the last decades, leading to a release of metals and metalloids into the environment. Sediment samples were taken in the vicinity of two mines and analyzed. Extraction of metals and metalloids from sediments was carried out using single extraction procedures, acidic (HNO₃), and complexation (EDTA) leaching, in order to determine the mobility of trace elements. Results indicated that acidic extraction at low pH values increased the leachability of trace elements. EDTA showed a higher bioavailability of metals in sediments than acidic extraction under similar pH conditions because of its greater leaching capacity. This is an important issue in view of risk assessment analysis. The highest extractability was observed for Cd in all sediments with up to 90% of extraction after 1 h. The mobility index analysis indicated that faster kinetic leachability of some trace elements leads to a higher mobility in sediments, especially those near the active gold extraction mine. The ecological risk assessment suggested that the four river sediments were at high and very high risk levels, indicating that sediment contamination is an issue of environmental concern in the Jequetepeque basin of northern Peru.     

Phytoremediation of toxic trace elements in soil and water

Toxic heavy metals and metalloids, such as cadmium, lead, mercury, arsenic, and selenium, are constantly released into the environment. There is an urgent need to develop low-cost, effective, and sustainable methods for their removal or detoxification. Plant-based approaches, such as phytoremediation, are relatively inexpensive since they are performed in situ and are solar-driven. In this review, we discuss specific advances in plant-based approaches for the remediation of contaminated water and soil. Dilute concentrations of trace element contaminants can be removed from large volumes of wastewater by constructed wetlands. We discuss the potential of constructed wetlands for use in remediating agricultural drainage water and industrial effluent, as well as concerns over their potential ecotoxicity. In upland ecosystems, plants may be used to accumulate metals/metalloids in their harvestable biomass (phytoextraction). Plants can also convert and release certain metals/metalloids in a volatile form (phytovolatilization). We discuss how genetic engineering has been used to develop plants with enhanced efficiencies for phytoextraction and phytovolatilization. For example, metal-hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate, and detoxify metals and metalloids represent an important reservoir of unique genes that could be transferred to fast-growing plant species for enhanced phytoremediation. There is also a need to develop new strategies to improve the acceptability of using genetically engineered plants for phytoremediation.     

Phytoremediation of toxic trace elements in soil and water

Toxic heavy metals and metalloids, such as cadmium, lead, mercury, arsenic, and selenium, are constantly released into the environment. There is an urgent need to develop low-cost, effective, and sustainable methods for their removal or detoxification. Plant-based approaches, such as phytoremediation, are relatively inexpensive since they are performed in situ and are solar-driven. In this review, we discuss specific advances in plant-based approaches for the remediation of contaminated water and soil. Dilute concentrations of trace element contaminants can be removed from large volumes of wastewater by constructed wetlands. We discuss the potential of constructed wetlands for use in remediating agricultural drainage water and industrial effluent, as well as concerns over their potential ecotoxicity. In upland ecosystems, plants may be used to accumulate metals/metalloids in their harvestable biomass (phytoextraction). Plants can also convert and release certain metals/metalloids in a volatile form (phytovolatilization). We discuss how genetic engineering has been used to develop plants with enhanced efficiencies for phytoextraction and phytovolatilization. For example, metal-hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate, and detoxify metals and metalloids represent an important reservoir of unique genes that could be transferred to fast-growing plant species for enhanced phytoremediation. There is also a need to develop new strategies to improve the acceptability of using genetically engineered plants for phytoremediation.

     

Metalloids in plants: A systematic discussion beyond description

Metalloids represent a wide range of elements with intermediate physiochemical properties between metals and non-metals. Many of the metalloids, like boron, selenium, and silicon are known to be essential or quasi-essential for plant growth. In contrast, metalloids viz. arsenic and germanium are toxic to plant growth. The toxicity of metalloids largely depends on their concentration within the living cells. Some elements, at low concentration, may be beneficial for plant growth and development; however, when present at high concentration, they often exert negative effects. In this regard, understanding the molecular mechanisms involved in the uptake of metalloids by roots, their subsequent transport to different tissues and inter/intra-cellular redistribution has great importance. The mechanisms of metalloids' uptake have been well studied in plants. Also, various transporters, as well as membrane channels involved in these processes, have been identified. In this review, we have discussed in detail the aspects concerning the positive/negative effects of different metalloids on plants. We have also provided a thorough account of the uptake, transport, and accumulation, along with the molecular mechanisms underlying the response of plants to these metalloids. Additionally, we have brought up the previous theories and debates about the role and effects of metalloids in plants with insightful discussions based on the current knowledge.     

The Sequential Application of Macroalgal Biosorbents for the Bioremediation of a Complex Industrial Effluent

Fe-treated biochar and raw biochar produced from macroalgae are effective biosorbents of metalloids and metals, respectively. However, the treatment of complex effluents that contain both metalloid and metal contaminants presents a challenging scenario. We test a multiple-biosorbent approach to bioremediation using Fe-biochar and biochar to remediate both metalloids and metals from the effluent from a coal-fired power station. First, a model was derived from published data for this effluent to predict the biosorption of 21 elements by Fe-biochar and biochar. The modelled outputs were then used to design biosorption experiments using Fe-biochar and biochar, both simultaneously and in sequence, to treat effluent containing multiple contaminants in excess of water quality criteria. The waste water was produced during ash disposal at an Australian coal-fired power station. The application of Fe-biochar and biochar, either simultaneously or sequentially, resulted in a more comprehensive remediation of metalloids and metals compared to either biosorbent used individually. The most effective treatment was the sequential use of Fe-biochar to remove metalloids from the waste water, followed by biochar to remove metals. Al, Cd, Cr, Cu, Mn, Ni, Pb, Zn were reduced to the lowest concentration following the sequential application of the two biosorbents, and their final concentrations were predicted by the model. Overall, 17 of the 21 elements measured were remediated to, or below, the concentrations that were predicted by the model. Both metalloids and metals can be remediated from complex effluent using biosorbents with different characteristics but derived from a single feedstock. Furthermore, the extent of remediation can be predicted for similar effluents using additive models.     

Pyridine-2,6-bis(thiocarboxylic acid) produced by Pseudomonas stutzeri KC reduces and precipitates selenium and tellurium oxyanions

The siderophore of Pseudomonas stutzeri KC, pyridine-2,6-bis(thiocarboxylic acid) (pdtc), is shown to detoxify selenium and tellurium oxyanions in bacterial cultures. A mechanism for pdtc's detoxification of tellurite and selenite is proposed. The mechanism is based upon determination using mass spectrometry and energy-dispersive X-ray spectrometry of the chemical structures of compounds formed during initial reactions of tellurite and selenite with pdtc. Selenite and tellurite are reduced by pdtc or its hydrolysis product H(2)S, forming zero-valent pdtc selenides and pdtc tellurides that precipitate from solution. These insoluble compounds then hydrolyze, releasing nanometer-sized particles of elemental selenium or tellurium. Electron microscopy studies showed both extracellular precipitation and internal deposition of these metalloids by bacterial cells. The precipitates formed with synthetic pdtc were similar to those formed in pdtc-producing cultures of P. stutzeri KC. Culture filtrates of P. stutzeri KC containing pdtc were also active in removing selenite and precipitating elemental selenium and tellurium. The pdtc-producing wild-type strain KC conferred higher tolerance against selenite and tellurite toxicity than a pdtc-negative mutant strain, CTN1. These observations support the hypothesis that pdtc not only functions as a siderophore but also is involved in an initial line of defense against toxicity from various metals and metalloids.     

The National Distribution Pattern and Factors Affecting Heavy Metals in Sediments of Water Systems in China

Heavy metal discharge has become one of the most serious environmental problems due to extensive industrialization. Sixty eight sediment samples from four wetlands were collected to analyze the regional factors affecting metal deposition. Meanwhile, a national sediment data collection based on relevant publications was developed covering the period from 2000 to 2016 to study the metal distribution in China. Principal metals assessed in this study are Cr, Cd, Cu, Pb, Zn, As, and Ni. At regional scale, the accumulation of Pb and Cd is significantly higher in surface than in subsurface sediments. At the national scale, heavy metals tend to increase with the increase in precipitation from 600 to 1500 mm. Further, metal deposition in the main river basins in China shows an increase trend from northern to southern China, and follows the order of: Pearl River > Yangste River > Yellow River > Hai River and Liao River. Cluster analyses show that these river basins contribute a large proportion of heavy metals to coastal metal deposition, which follows the order of: South Sea > East Sea > Bohai Sea > Yellow Sea. In general, metal deposition in sediments of water systems increases from northern to southern China irrespective of in-land area or coastal seas.     

Transport and distribution of trace elements and other selected inorganic constituents by suspended particulates in the Salton Sea Basin, California, 2001

In order to examine the transport of contaminants associated with river-derived suspended particles in the Salton Sea, California, large volume water samples were collected in transects established along the three major rivers emptying into the Salton Sea in fall 2001. Rivers in this area carry significant aqueous and particulate contaminant loads derived from irrigation water associated with the extensive agricultural activity, as well as wastewater from small and large municipalities. A variety of inorganic constituents, including trace metals, nutrients, and organic carbon were analyzed on suspended material isolated from water samples collected at upriver, near-shore, and off-shore sites established on the Alamo, New, and Whitewater rivers. Concentration patterns showed expected trends, with river-borne metals becoming diluted by organic-rich algal particles of lacustrine origin in off-shore stations. More soluble metals, such as cadmium, copper, and zinc showed a more even distribution between sites in the rivers and off-shore in the lake basin. General distributional trends of trace elements between particulate and aqueous forms were discerned by combining metal concentration data for particulates from this study with historical aqueous metals data. Highly insoluble trace metals, such as iron and aluminum, occurred almost entirely in the particulate phase, while major cations and approximately 95% of selenium were transported in the soluble phase. Evidence for greater reducing conditions in the New compared to the Alamo River was provided by the greater proportion of reduced (soluble) manganese in the New River. Evidence of bioconcentration of selenium and arsenic within the lake by algae was provided by calculating “enrichment” concentration ratios from metal concentrations on the algal-derived particulate samples and the off-shore sites. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005 Roy A. Schroeder—Retired.     

Organochlorine pesticides, polychlorinated biphenyls, metals, and trace elements in waterbird eggs, Salton Sea, California, 2004

The Salton Sea is a highly eutrophic, hypersaline terminal lake that receives inflows primarily from agricultural drainages in the Imperial and Coachella valleys. Impending reductions in water inflow at Salton Sea may concentrate existing contaminants which have been a concern for many years, and result in higher exposure to birds. Thus, waterbird eggs were collected and analyzed in 2004 and compared with residue concentrations from earlier years; these data provide a base for future comparisons. Eggs from four waterbird species (black-crowned night-heron [Nycticorax nycticorax], great egret [Ardea alba], black-necked stilt [Himantopus mexicanus], and American avocet [Recurvirostra Americana]) were collected. Eggs were analyzed for organochlorine pesticides, polychlorinated biphenyls (PCBs), metals, and trace elements, with current results compared to those reported for eggs collected from the same species and others during 1985–1993. The two contaminants of primary concern were p,p′-DDE (DDE) and selenium. DDE concentrations in night-heron and great egret eggs collected from the northwest corner of Salton Sea (Whitewater River delta) decreased 91 and 95%, respectively, by 2004, with a concomitant increase in eggshell thickness for both species. Decreases in bird egg DDE levels paralleled those in tissues of tilapia (Oreochromis mossambicus × O. urolepis), an important prey species for herons and egrets. Despite most nests of night-herons and great egrets failing in 2004 due to predation, predicted reproductive effects based on DDE concentrations in eggs were low or negligible for these species. The 2004 DDE findings were in dramatic contrast to those in the past decade, and included an 81% decrease in black-necked stilt eggs, although concentrations were lower historically than those reported in night-herons and egrets. Selenium concentrations in black-necked stilt eggs from the southeast corner of Salton Sea (Davis Road) were similar in 1993 and 2004, with 4.5–7.6% of the clutches estimated to be selenium impaired during both time periods. Because of present selenium concentrations and future reduced water inflow, the stilt population is of special concern. Between 1992 and 1993 and 2004 selenium in night-heron and great egret eggs from the Whitewater River delta at the north end of the Sea decreased by 81 and 55%, respectively. None of the night-heron or egret eggs collected in 2004 contained selenium concentrations above the lowest reported effect concentration (6.0 μg/g dw). Reasons for selenium decreases in night-heron and egret eggs are unknown. Other contaminants evaluated in 2004 were all below known effect concentrations. However, in spite of generally low contaminant levels in 2004, the nesting populations of night-herons and great egrets at Salton Sea were greatly reduced from earlier years and snowy egrets (Egretta thula) were not found nesting. Other factors that include predation, reduced water level, diminished roost and nest sites, increased salinity, eutrophication, and reduced fish populations can certainly influence avian populations. Future monitoring, to validate predicted responses by birds, other organisms, and contaminant loadings associated with reduced water inflows, together with adaptive management should be the operational framework at the Salton Sea. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Risk assessment of heavy metal toxicity through contaminated vegetable from sewage water: Implications for populace health

The present investigation was carried out to evaluate the levels of metals and metalloids in okra (Abelmoschus esculentus) irrigated with city wastewater. Soil and vegetable samples from two different sites irrigated with wastewater were wet-digested and analyzed. Arsenic (As) was found higher at both sites and Cr was many-fold lower at both sampling sites. Among all heavy metals, Mn and Zn were abundant. Highest value of coefficient factor was found for Cr and the lowest for Cd. The high transfer value was recorded for Cu at site-I and for Ni at site-II. Copper and Se showed negative and significant correlations between soil and vegetable, whereas Mn, Zn, As, Cd, Cr, and Ni showed positive but non-significant correlations. Pollution load index in this vegetable was found to be higher for Cd and lower for Cu. Health risk index at site-I was in the order of As > Mn > Mo > Pb > Cd > Ni > Zn > Se > Fe > Co > Cr > Cu, whereas the same order was observed at site-II of the sampling locations. Thus, the health risks of metals through ingestion of vegetables were of great concern in the study area.     

Risk assessment of heavy metal and metalloid toxicity through a contaminated vegetable (Cucurbita maxima) from wastewater irrigated area: A case study for a site-specific risk assessment in Jhang,Pakistan

The present research was conducted in district Jhang, Pakistan, to evaluate the concentration of metals/metalloids in soil and pumpkin (Cucurbita maxima) irrigated with domestic wastewater. Data revealed that the levels of metals and metalloids in soil samples from two different sites were below the safe limits except Cd, whereas, in the vegetable, the concentrations of As, Se, Ni, Mo, Pb, Mn, and Cu were above the safe limits. The levels of 12 metals and metalloids in the soil were ranged between 0.14 to 22.76 mg/kg at site-I and 0.16 to 22.13 mg/kg at site-II. The levels of these metals in the vegetable were found 0.35 to 61.13 mg/kg at site-I and 0.31 to 53.63 mg/kg at site-II. The transfer factor at both sites was highest for As and Co. The pollution load index recorded for Se, Cu, Cd, Mo, Pb, and Co was greater than 1. The daily intake of As, Mn, and Mo was above the oral reference dose, which reflects that the intake of pumpkin is not safe for the inhabitants of the selected sites. The control measures should be taken to phytoextract heavy metals and metalloids from polluted sites so as to reduce the health risks.     

Pyridine-2,6-Bis(Thiocarboxylic Acid) Produced by Pseudomonas stutzeri KC Reduces and Precipitates Selenium and Tellurium Oxyanions

The siderophore of Pseudomonas stutzeri KC, pyridine-2,6-bis(thiocarboxylic acid) (pdtc), is shown to detoxify selenium and tellurium oxyanions in bacterial cultures. A mechanism for pdtc's detoxification of tellurite and selenite is proposed. The mechanism is based upon determination using mass spectrometry and energy-dispersive X-ray spectrometry of the chemical structures of compounds formed during initial reactions of tellurite and selenite with pdtc. Selenite and tellurite are reduced by pdtc or its hydrolysis product H₂S, forming zero-valent pdtc selenides and pdtc tellurides that precipitate from solution. These insoluble compounds then hydrolyze, releasing nanometer-sized particles of elemental selenium or tellurium. Electron microscopy studies showed both extracellular precipitation and internal deposition of these metalloids by bacterial cells. The precipitates formed with synthetic pdtc were similar to those formed in pdtc-producing cultures of P. stutzeri KC. Culture filtrates of P. stutzeri KC containing pdtc were also active in removing selenite and precipitating elemental selenium and tellurium. The pdtc-producing wild-type strain KC conferred higher tolerance against selenite and tellurite toxicity than a pdtc-negative mutant strain, CTN1. These observations support the hypothesis that pdtc not only functions as a siderophore but also is involved in an initial line of defense against toxicity from various metals and metalloids.     

Volatilisation of metals and metalloids: An inherent feature of methanoarchaea?

As shown by recent studies, anaerobic members of Archaea and Bacteria are involved in processes that transform ionic species of metals and metalloids (arsenic, antimony, bismuth, selenium, tellurium and mercury) into volatile and mostly toxic derivatives (mainly methyl derivatives or hydrides). Since the fact that these transformations proceed in both environmental settings and in parts of the human body, we have to consider that these processes also interfere directly with human health. The diversity of the volatile derivatives produced and their emission rates were significantly higher in methanoarchaeal than in bacterial strains, which supports the pivotal role of methanoarchaea in transforming metals and metalloids (metal(loid)s) into their volatile derivatives. Compared with methanoarchaea, 14 anaerobic bacterial strains showed a significantly restricted spectrum of volatilised derivatives and mostly lower production rates of volatile bismuth and selenium derivatives. Since methanoarchaea isolated from the human gut (Methanosphaera stadtmanae, Methanobrevibacter smithii) showed a higher potential for metal(loid) derivatisation compared to bacterial gut isolates, we assume that methanoarchaea in the human gut are mainly responsible for the production of these volatile derivatives. The observation that trimethylbismuth ((CH(3))(3)Bi), the main volatile derivative of bismuth produced in human feces, inhibited growing cultures of Bacteroides thetaiotaomicron, a representative member of the human physiological gut flora, suggests that these volatiles exert their toxic effects on human health not only by direct interaction with host cells but also by disturbing the physiological gut microflora.     

Selenate reduction rates and kinetics across depth in littoral sediment of the Salton Sea,California

To predict selenium cycling in sediments, it is crucial to identify and quantify the processes leading to selenium sequestration in sediments. More specifically, it is essential to obtain environmentally-relevant kinetic parameters for selenium reduction and information on how they spatially vary in sediments. The Salton Sea (California, USA) is an ideal model system to examine selenium processes in sediments due to its semi-enclosed conditions and increasing selenium concentration over the last century. Selenium enters the Salton Sea mainly as selenate and might be sequestered in the sediment through microbial reduction. To determine the potential selenium sequestration of Salton Sea littoral sediments and which sediment properties are controlling selenate reduction kinetics, we determined the centimeter-scale vertical distribution of potential selenate reduction rates and apparent kinetic parameters (maximum selenate reduction rates, V_max, and selenate half-saturation concentration, K_m) using flow-through reactor (FTR) experiments. We compared sediments from two littoral sites (South and North) and four depth intervals (0–2, 2–4, 4–6 and 6–8 cm). Furthermore, we characterized the selenium fractions in the sediment recovered from the FTR experiments to identify the processes leading to the sequestration of selenium. Our results reveal higher potential for selenium reduction and sequestration in the topmost sediment (0–2 cm) suggesting that microorganisms inhabiting surface sediment are well adapted to reduce selenate entering the Salton Sea. As apparent K_m values (103–2144 µM) exceed the average selenium concentration in the overlying water (6–25 nM), in situ selenate reduction is limited by the low availability of selenate and the resident selenate-reducing microorganisms operate well below their V_max (11 and 43 nmol cm^?3 h^?1). Selenium speciation after FTR experiments confirms the primary sequestration of reduced biomass-associated and elemental selenium (68–99% of total selenium) in the sediment. Further, the absence of correlation between the tested sediment physical (porosity, bulk density, clay content), chemical (C_org, N_tot, total selenium content) and biological characteristics (abundance of culturable selenate-reducers) with the kinetic parameters of selenate reduction indicates that these sediment characteristics cannot be used as predictors of apparent V_max or K_m. Conclusively, microbial selenate reduction is an important, if not the primary process, leading to the sequestration of reduced selenium in the Salton Sea sediments and making the surficial Salton Sea sediments an important selenium sink.     

Metals and metalloids in a first order stream of the Atlantic rainforest: abiotic matrices,bioaccumulation in fishes and human health risk assessment

Background and aimMetals and metalloids have been found in several streams and rivers from the Atlantic Rainforest (ARF), one of the world´s leading biodiversity hotspot, which may represent a risk for environmental and human health. The aims of this study were: 1) to evaluate the accumulation and distribution of 24 trace elements in water, sediments and fish tissues (muscle and gills) of sixteen species from the Atlantic Rainforest, 2) to explore bioaccumulation patterns in fish tissues and abiotic matrices, and 3) to assess the impact of metal and metalloids on the human health from water and fish consumption.MethodsWater, sediments and fish samples were collected from Ramos Stream (Misiones Province, Argentina). The concentrations of Ag, Al, As, Ba, Be, Cd, Co, Cr, Cs, Cu, Fe, Ga, Hg, Li, Mg, Mn, Ni, Pb, Se, Sr, Ti, U, V and Zn were determined by Quadrupole Inductively Coupled Plasma Mass Spectrometry. Bioaccumulation factors (BAFs) were used to evaluate bioaccumulation of metals and metalloids in relation to water and sediment. The Hazard Quotient (HQ), Hazard Index (HI) and Target Hazard Quotient (THQ, general and fisherman populations) were calculated to assess the non-carcinogenic human health risk from water and fish consumption.ResultsThe concentrations of several elements in water and sediment were higher than the international guidelines for aquatic biota protection. Levels of As, Pb and Zn in muscle and gills were above national and international guidelines for human consumption. The bioaccumulation factors ranged from 749 to 13,029 being higher in gills than in muscle. The HQ and HI ranged from 0.001 to 0.015. The THQ for each element and total THQ values were lower than 0.1.ConclusionBioaccumulation factor suggests that several species have a moderate capacity to incorporate some metals and metalloids from the abiotic matrices. According to the HI and THQ values found, there is no risk to human health from consumption of water and fish.