Seawater

Analysis of molybdenum, tungsten, and vanadium in surface water of the Atlantic Ocean using solid phase extraction with 8-hydroxyquinoline and ICP MS determination

An analytical technique is proposed to determine ultratrace concentrations of Mo, V, and W found in seawater using mass spectrometry with inductively coupled plasma (ICP MS) after preliminary concentration by solid-phase extraction of metal complexes with 8-hydroxyquinoline (8-HQ) on C18 octadecyl silica. The technique utilizes 150 mL of a water sample. A preconcentration factor 50 is obtained. The detection limits are 0.25 nmol/kg, 0.041 nmol/kg, and 5 pmol/kg for Mo, V, and W, respectively. Dissolved Mo, V, and W concentrations in surface seawater from Atlantic Ocean transect were determined. The concentrations ranges along the transect were: 91-108 nmol/kg for Mo, 28-35 nmol/kg for V, and 55-75 pmol/kg for W. The Mo/W ratio varied from 1300 to 1800.

Rimskaya-Korsakova, M. N., Berezhnaya, E. D., and Dubinin, A. V.,Analysis of molybdenum, tungsten, and vanadium in surface water of the Atlantic Ocean using solid phase extraction with 8-hydroxyquinoline and ICP MS determination, Oceanology, 2017, 57, 530-538.

Tungsten-molybdenum fractionation in estuarine environments

Dissolved tungsten (W) and molybdenum (Mo) concentrations were measured in surface waters and sediment pore waters of Terrebonne Bay, a shallow estuary in the Mississippi River delta, to investigate the biogeochemical processes that fractionate these Group 6 elements relative to one another during transit from weathering to sedimentary environments.

Although many of the chemical properties of W and Mo are similar, the two elements behave autonomously, and the fractionation mechanisms are only partly understood.

In sulfidic pore waters, dissolved Mo is depleted relative to river water-seawater mixtures, whereas dissolved W is >10-fold enriched. Reductive dissolution of poorly crystalline phases like ferrihydrite, which is a preferential host of W relative to Mo in grain coatings on river-borne particles, can explain the dissolved W enrichment. Dissolved W becomes increasingly enriched as H₂S(aq) rises above about 60 mu M due to transformation of WO₄^2-to thio-tungstates as well as to additional reductive dissolution of phases that host W.

In contrast, as rising sulfide transforms MoO₄^2-to thiomolybdates in pore waters, dissolved Mo is suppressed, probably owing to equilibration with an Fe-Mo-S phase. This putative phase appears to control the aqueous ion product, Q = [Fe²⁺][MoS₄^2-](0.6)[H₂S₀](0.4)/[H+](0.8), at a value of 10(-7.78).

Concentrations of dissolved W and Mo in pore waters bear no relation to concentrations in surface waters of the same salinity.

In surface waters, dissolved Mo is nearly conserved in the estuarine mixing zone.

Dissolved W appears also to be conserved except for several cases where W may have been enhanced by exchange with underlying, W-rich pore waters.

With increasing salinity, the molar Mo/W ratio rises from about 10 to about 1000 in surface waters whereas it is mostly

Differences in two chemical properties may account for this fractionation of Mo with respect to W; Mo VI is more susceptible to reduction than W VI, but the latter is more prone to adopting octahedral coordination. We propose that the first difference facilitates Mo but not W precipitation in sulfidic sediments, whereas the second explains tungsten's proportionately greater sequestration on river-borne particles and its subsequent release to sulfidic pore waters after the particles are deposited in the delta and become subject to reductive dissolution during diagenesis. (C) 2016 Elsevier Ltd. All rights reserved.

Mohajerin, T. J_., Helz, G. R_., and Johannesson, K. H_.,Tungsten-molybdenum fractionation in estuarine environments, Geochimica Et Cosmochimica Acta, 2016, 177, 105-119.

Metals in SURFACE WATER of Ukraine: the migration forms, features of distribution between the abiotic components of aquatic ecosystems, and potential bioavailability

We have generalized the results of long-term studies of coexisting forms of a series of metals (Al, Fe, Mn, Zn, Cu, Cr, Pb, Mo, Cd, and V) in surface water bodies of Ukraine, differing in the hydrological regime and the water chemical composition (rivers, reservoirs, lakes, and ponds). The studied metals content has ranged widely, the concentrations of aluminum, iron, and manganese being typically the highest, and the concentration of molybdenum, vanadium, and cadmium being typically the lowest.

The ratio between the suspended and the dissolved forms of the metals has been established.

Iron and aluminum migrate mostly as part of the suspended matter, whereas the other metals mainly migrate in the dissolved state.

The dissolved manganese form predominates in the water bodies under anaerobic conditions.

Copper and molybdenum are present almost always in the dissolved state, regardless of the water body type.

The data on the relative content of the labile metal fraction (potentially toxic to aquatic organisms) are reported. The relatively low content of this fraction has been found to be majorly owing to the metal ions complexing with natural organic ligands. The humic compounds, the most widespread group of natural organic compounds, play the primary role in the complexation. Even metals with variable oxidation state (Cr, Mo, and V) are found mainly in the form of anionic complexes with the humic substances. Carbohydrates are also involved in the metals binding in the highly bioproductive water bodies, thus increasing the mass fraction of the neutral complexes during the summer and autumn periods.

The molecular weight distribution of anionic metal complexes has been discussed; the substantial part of the metals constitutes the compounds with the molecular weight of below 5.0 kDa.

Linnik, P. N., Zhezherya, V. A., Linnik, R. P., Ignatenko, II, and Zubenko, I. B.,Metals in surface water of Ukraine: the migration forms, features of distribution between the abiotic components of aquatic ecosystems, and potential bioavailability, Russian Journal of General Chemistry, 2015, 85, 2965-2984.

Molybdenum and zinc stable isotope variation in MINING WASTE rock drainage and waste rock at the Antamina mine, Peru

The stable isotope composition of molybdenum (Mo) and zinc (Zn) in mine wastes at the Antamina Copper-Zn-Mo mine, Peru, was characterized to investigate whether isotopic variation of these elements indicated metal attenuation processes in mine drainage.

Waste rock and ore minerals were analyzed to identify the isotopic composition of Mo and Zn sources, namely molybdenites (MoS₂) and sphalerites (ZnS). Molybdenum and Zn stable isotope ratios are reported relative to the NIST-SRM-3134 and PCIGR-1 Zn standards, respectively.

Delta⁹⁸Mo among molybdenites ranged from -0.6 to +0.6 per thousand (n=9) while sphalerites showed no delta⁶⁶Zn variations (0.11+/-0.01 per thousand, 2 SD, n=5).

Mine drainage samples from field waste rock weathering experiments were also analyzed to examine the extent of isotopic variability in the dissolved phase. Variations spanned 2.2 per thousand in delta⁹⁸Mo (-0.1 to +2.1 per thousand) and 0.7 per thousand in delta⁶⁶Zn (-0.4 to +0.3 per thousand) in mine drainage over a wide pH range (pH2.2-8.6).

Lighter delta⁶⁶Zn signatures were observed in alkaline pH conditions, which was consistent with Zn adsorption and/or hydrozincite (Zn₅(OH)₆(CO₃)₂) formation. However, in acidic mine drainage Zn isotopic compositions reflected the value of sphalerites.

In addition, molybdenum isotope compositions in mine drainage were shifted towards heavier values (0.89+/-1.25 per thousand, 2 SD, n=16), with some overlap, in comparison to molybdenites and waste rock (0.13+/-0.82 per thousand, 2 SD, n=9).

The cause of heavy Mo isotopic signatures in mine drainage was more difficult to resolve due to isotopic heterogeneity among ore minerals and a variety of possible overlapping processes including dissolution, adsorption and secondary mineral precipitation.

This study shows that variation in metal isotope ratios are promising indicators of metal attenuation. Future characterization of isotopic fractionation associated to key environmental reactions will improve the power of Mo and Zn isotope ratios to track the fate of these elements in mine drainage.

Skierszkan, E. K., Mayer, K. U., Weis, D., and Beckie, R. D.,Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine, Peru, The Science of the total environment, 2016, 550, 103-113.

GROUNDWATER Molybdenum from Emerging Industries in Taiwan

This study determined the influence of emerging industries development on molybdenum (Mo) groundwater contamination.

A total of 537 groundwater samples were collected for Mo determination, including 295 samples from potentially contaminated areas of 3 industrial parks in Taiwan and 242 samples from non-potentially contaminated areas during 2008-2014.

Most of the high Mo samples are located downstream from a thin film transistor-liquid crystal display (TFT-LCD) panel factory.

Mean groundwater Mo concentrations from potentially contaminated areas (0.0058 mg/L) were significantly higher (p < 0.05) than those from non-potentially contaminated areas (0.0022 mg/L). The highest Mo wastewater concentrations in the effluent from the opto-electronics industry and following wastewater batch treatment were 0.788 and 0.0326 mg/L, respectively. This indicates that wastewater containing Mo is a possible source of both groundwater and surface water contamination. Nine samples of groundwater exceed the World Health Organization's suggested drinking water guideline of 0.07 mg/L. A non-carcinogenic risk assessment for Mo in adults and children using the Mo concentration of 0.07 mg/L yielded risks of 0.546 and 0.215, respectively.

These results indicate the importance of the development of a national drinking water quality standard for Mo in Taiwan to ensure safe groundwater for use.

According to the human health risk calculation, the groundwater Mo standard is suggested as 0.07 mg/L. Reduction the discharge of Mo-contaminated wastewater from factories in the industrial parks is also the important task in the future.

Tsai, K. S., Chang, Y. M., Kao, J. C. M., and Lin, K. L.,Groundwater Molybdenum from Emerging Industries in Taiwan, Bulletin of Environmental Contamination and Toxicology, 2016, 96, 102-106.

Acid extraction of molybdenum, nickel and cobalt from MINERAL SLUDGE generated by rainfall water at a metal recycling plant

This study investigated the leaching yields of Mo, Ni and Co from a mineral sludge of a metal recycling plant generated by rainfalls.

The investigated mineral sludge had a complex heterogeneous composition, consisting of particles of settled soil combined with metal-bearing particles (produced by catalysts, metallic oxides and battery recycling).

The leaching potential of different leaching reagents (stand-alone strong acids (HNO₃ (68%), H₂SO₄ (98%) and HCl (36%)) and acid mixtures (aqua regia (nitric + hydrochloric (1:3)), nitric + sulphuric (1:1) and nitric + sulphuric + hydrochloric (2:1:1)) was investigated at changing operational parameters (solid-liquid (S/L) ratio, leaching time and temperature), in order to select the leaching reagent which achieves the highest metal leaching yields. Sulphuric acid (98% H₂SO₄) was found to be the leachant with the highest metal leaching potential.

The optimal leaching conditions were a three-stage successive leaching at 80 degrees C with a leaching time of 2 h and S/L ratio of 0.25 g L^-1. Under these conditions, the achieved mineral sludge sample leaching yields were 85.5%, 40.5% and 93.8% for Mo, Ni and Co, respectively.

The higher metal leaching potential of H₂SO₄ in comparison with the other strong acids/acid mixtures is attributed to the fact that H₂SO₄ is a diacidic compound, thus it has more H(+) ions, resulting in its stronger oxidizing power and corrosiveness.

Vemic, M., Bordas, F., Guibaud, G., Comte, S., Joussein, E., Lens, P. N., and Hullebusch, E. D.,Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant, Environmental technology, 2016, 37, 630-9.

Cement

Binding and leaching of trace elements in PORTLAND CEMENT pastes

Portland cement contains trace elements originating from the raw materials and the fuels used for cement production. The trace elements are bound to some extent during cement hydration. A small fraction remains dissolved in the pore solution. The dissolved fractions of antimony, barium, chromium, lead, molybdenum and vanadium were quantified in the course of hydration of four different Portland cements. The development of heavy metal concentrations signifies the relevant hydration products for the binding of heavy metals. For chromate and molybdate a substitution for sulfate in ettringite was found. Vanadium and antimony are most likely not bound in ettringite. Barium precipitates as barium sulfate. For lead no clear trends could be observed. Leaching experiments were carried out and the concentrations of the leachates were compared to pore solution concentrations to check if the solubility of the heavy metals is relevant or if the leaching process is controlled by diffusion. (C) 2015 Elsevier Ltd. All rights reserved.

Vollpracht, A., and Brameshuber, W.,Binding and leaching of trace elements in Portland cement pastes, Cement and Concrete Research, 2016, 79, 76-92.

The REACH [Registration, Evaluation, Authorisation & restriction of Chemicals] Molybdenum Consortium initiated an extensive research program in order to generate robust PNECs [Predicted No-Effect Concentrations], based on the SSD [Species-Sensitivity Distribution] approach, for both the freshwater and marine environments. This activity was part of the REACH dossier preparation and to form the basis for scientific dialogues with other national and international regulatory authorities.

Chronic ecotoxicity data sets for the freshwater and marine environments served as starting point for the derivation of PNECs for both compartments, in accordance with the recommended derivation procedures established by the European Chemicals Agency (ECHA).

The HC(5,50%)s [the concentrations hazardous to 5% of the species with 50% confidence limits] that were derived from the generated Species Sensitivity Distributions were 38.2 mg Mo/L and 5.75 mg Mo/L for the freshwater and marine water compartment, respectively.

Uncertainty analysis on both data sets and available data on bio-accumulation at high exposure levels justified an assessment factor of 3 on both HC(5.50%) leading to a PNEC(freshwater) of 12.7 mg Mo/L and a PNEC(marine) of 1.92 mg Mo/L.

As there are currently insufficient ecotoxicological data available for the derivation of PNECs in the sediment compartment, the equilibrium partitioning method was applied; typical R-D-values for both the freshwater and marine compartments were identified and combined with the respective PNEC, leading to a PNEC(sediment) of 22,600 mg/kg dry weight and 1980 mg/kg dry weight for freshwater and marine sediments, respectively.

The chronic data sets were also used for the derivation of FCVs [final chronic values] using the procedures that are outlined by the US Environmental Protection Agency for deriving such water benchmarks. Comparing PNECs with FCVs showed that both methodologies result in comparable protective concentration levels for molybdenum in the environment. (c) 2012 Elsevier B.V. All rights reserved. 23.

Heijerick, D. G.Regoli, L. Carey, S. The toxicity of molybdate to freshwater and marine organisms. II.Effects assessment of molybdate in the aquatic environment under REACH Science Of The Total Environment, 2012, 435, 179-187.

In a regulatory context, bioaccumulation or bioconcentration factors are used for considering secondary poisoning potential and assessing risks to human health via the food chain. In this paper, literature data on the bioaccumulation of molybdenum in the aquatic organisms are reviewed and assessed for relevance and reliability. The data available in the literature were generated at exposure concentrations below those recommended in the REACH registration dossiers for molybdenum compounds i.e. PNEC(freshwater) 12.7 mg Mo/L.

To address possible environmental concerns at regulatory-relevant molybdenum concentrations, both a field study and a laboratory study were conducted.

In the field study, whole body and organ-specific molybdenum levels were evaluated in fish (eel, stickleback, perch, carp bream, roach) held in the discharge water collector tanks of a molybdenum processing plant, containing a mean measured molybdenum level of 1.03 mg Mo/L.

In the laboratory study, rainbow trout were exposed to two different nominal molybdenum levels (1.0 and 12.7 mg Mo/L), for 60 days followed by a 60-day depuration period.

Whole body concentrations in rainbow trout during the exposure period were between <0.20 and 0.53 mg Mo/L.

Muscle tissue molybdenum concentrations in fish taken from both experiments remained below 0.2 mg/kg dry wt.

These studies show an inverse relationship between exposure concentration and bioconcentration or bioaccumulation factor for molybdenum. In aquatic organisms, and in fish in particular, internal molybdenum concentrations are maintained in the presence of variation in external molybdenum concentrations. These observations must be considered when evaluating potential risks associated with the bioconcentration and/or bioaccumulation of molybdenum in the aquatic environment. (c) 2012 Published by Elsevier B.V

Regoli, Lidia, Van Tilborg, Wim, Heijerick, Dagobert, Stubblefield, William, and Carey, Sandra, The bioconcentration and bioaccumulation factors for molybdenum in the aquatic environment from natural environmental concentrations up to the toxicity boundary, Science of the Total Environment, 2012, 435, 96-106.

[PNEC: Predicted No-Effect Concentration]

 One of the important methods of transport of molybdenum from the area of release is by water. Because of the effect of molybdenum on livestock the U.S. Committee on Water Quality Criteria has recommended a limit of 5 ug Mo/l in irrigation water for continuous use on all soils and 50 ug Mo/l for short term use on fine-textured soils., [U.S. Department of the Interior, 1968]. Other sources include the waste water from industrial processes, the transportation of ores and the distribution of sewage all of which can result in widespread addition of molybdenum in the environment.

U.S. Department of the Interior, 1968

Molybdate transport in groundwater is retarded by sorption, depending on the pH and the levels of phosphate and sulfate in the water.

Davis, J. A., Field Experiments. Proceedings Metal Speciation and Transport in Groundwaters, Jekyll Island, Georgia., 1989, Lewis Publ., Chelsea, Michigan.

Analysis

Trace amounts of molybdenum(VI) have been determined spectrophotometrically using 5,7-dibromo-8- hydroxyquinoline in alloys, steels, and environmental waters (inland and surface), biological samples (human blood and urine), and soil samples. The method has high precision and accuracy (S = +/- 0.01 for 0.5 mug mL(-1))

Ahmed, M.J. and Haque, M. E., A rapid spectrophotometric method for the determination of molybdenum in industrial, environmental, biological and soil samples using 5,7-dibromo-8-hydroxyquinoline, Analytical Sciences, 2002, 18, 433-439.

A chitosan resin functionalized with 3-nitro-4-amino benzoic acid moiety (CCTS-NABA resin) adsorbed metal ions vanadium, gallium, arsenic, selenium, silver, bismuth, thorium, tungsten, tin, tellurium, copper, and molybdenum. The resin was selective toward molybdenum at pH 3-4. The resin was used for the adsorption/collection of molybdenum in river water and seawater samples. Concentrations in river water samples were 0.84 and 0.95 ppb Mo (ng g^-1) and in seawater about 9 ppb

Sabarudin, A., Oshima, M., Noguchi, O., and Motomizu, S., Functionalization of chitosan with 3-nitro-4-amino benzoic acid moiety and its application to the collection/concentration of molybdenum in environmental water samples, Talanta, 2007, 73, 831-837.

Natural variations in the isotopic composition of molybdenum (Mo) are showing increasing potential as a tool in geochemistry. Although the ocean is an important reservoir of Mo, data on the isotopic composition of Mo in seawater are scarce. We have recently developed a new method for the precise determination of Mo isotope ratios on the basis of preconcentration using a chelating resin and measurement by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), which allows its to measure every stable Mo isotope (Nakagawa et al., 2008). In this study, 172 seawater samples obtained from 9 stations in the Pacific, Atlantic, and Southern Oceans were analyzed, giving global coverage and the first full depth-profiles. The average isotope composition in delta Mo-A/95 (relative to a Johnson Matthey Mo standard solution) was as follows: delta Mo-92/95 =3D -2.54 += /- 0.16 parts per thousand (2SD), delta Mo-94/95 =3D -0.73 +/- 0.19 parts p= er thousand, delta Mo-96/95 =3D 0.85 +/- 0.07 parts per thousand, delta Mo-97/95 =3D 1.68 +/- 0.08 parts per thousand, delta Mo-98/95 =3D 2.48 += /- 0.10 parts per thousand, and delta Mo-100/95 =3D 4.07 +/- 0.18 parts per thousand. The delta values showed an excellent linear correlation with atomic mass of Mo-A (R-2 =3D 0.999). Three-isotope plots for the Mo isotopes were fitted with straight lines whose slopes agreed with theoretical values for mass-dependent isotope fractionation. These results demonstrate that Mo isotopes are both uniformly distributed and follow a mass-dependent fractionation law in the modern oxic ocean. In addition, Mo isotopic analysis revealed that delta Mo-98/95 of the standard used in this study was 0.117 +/- 0.009 parts per thousand lighter than the Mo standard that was used by Archer and Vance (2008). A common Mo standard is urgently required for the precise comparison of Mo isotopic compositions measured in different laboratories. On the other hand, our results strongly support the possibility of seawater as an international reference material for Mo isotopic composition

Nakagawa, Yusuke, Takano, Shotaro, Firdaus, M. Lutfi, Norisuye, Kazuhiro, Hirata, Takafumi, Vance, Derek, and Sohrin, Yoshiki, The molybdenum isotopic composition of the modern ocean, Geochemical Journal, 2012, 46, 131-141.

Distribution of heavy metals in the coastal area of Abu Dhabi in the United Arab Emirates

Fifty-seven sediment samples were collected from Abu Dhabi coastal area, United Arab Emirates (UAE). The concentrations of heavy metals including antimony, arsenic, barium, cadmium, cobalt, copper, mercury, lead, molybdenum, nickel and zinc were obtained using Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) and X-ray fluorescence. Heavy metal contaminations in Abu Dhabi had increased since 2004. Nevertheless, the enrichment factors, geoaccumulation indices and the pollution load index of 0.3 showed no pollution with any of the measured metals except arsenic. (C) 2015 Elsevier Ltd. All rights reserved.

Al Rashdi, S., Arabi, A. A., Howari, F. M., and Siad, A.,Distribution of heavy metals in the coastal area of Abu Dhabi in the United Arab Emirates, Marine Pollution Bulletin, 2015, 97, 494-498.

A minicolumn was filled with ethyl vinyl acetate turnings as the adsorbent. Molybdenum was retained on the minicolumn without further complexation; sample throughput was 12 samples per hour; precision for six replicate measurements of a solution containing 20 mu g L-1 Mo was 3.5% relative standard deviation; limit of detection was 0.04 mu g L-1.

Escudero, L., Gil, R. A., Gasquez, J. A., Olsina, R. A., and Martinez, L. D., Trace molybdenum determination in drinking waters by USN-ICP-OES after solid phase extraction on ethyl vinyl acetate turnings-packed minicolumn, Atomic Spectroscopy, 2008, 29, 21-26.

Elevated pH increases solubility and leachability of Mo in water.
Acidic conditions decrease the transfer of Mo from soil to water. Acidic groundwater in contact with soil containing 800 mg Mo/kg has < 0.2 mg Mo/l.

Runnells, D.D., Kaback, D.S., and Thurman, E.M., Geochemistry and sampling of molybdenum in sediments, soils and plants in Colorado in Chappell, W.B., Peterson, K.K., eds. , Molybdenum in the Environment Vol. 2, New York, Elsevier, 1977.

Mo(VI) in environmental samples; e.g., soil, natural water and indoor airborne particulate has been determined by cathodic linear sweep stripping voltammetry. Molybdenum species are concentrated on the hanging mercury drop electrode (HMDE) using mixtures of nitrate and phosphate as supporting electrolytes. The detection limit found was 1 x 10^-8 M using 120 s as accumulation time. The precision ( relative standard deviation) was 1.4% with five replicates at 1 x 10^-6 M Mo(VI).The data refer to Mo concentrations in potable water in Egypt:
range of values from different souces 0.48 - 9.58 microg l^-1
tap water (Nile) 3.93
tap water (well) 5.76
natural water (Nile) after filtration 8.15

Ali, A.M.M., Ghandour, M. A., El Shatoury, S. A., and Ahmed, S. M., Adsorptive cathodic stripping voltammetric determination of molybdenum in synthetic solutions and environmental samples, Electroanalysis, 2000, 12, 155-158.
Mo in natural water Malinovsky, D., Hammarlund, D., Ilyashuk, B., Martinsson, O., and Gelting, J., Variations in the isotopic composition of molybdenum in freshwater lake systems, Chemical Geology, 2007, 236, 181-198.

A liquid core waveguide has been used to extend the sensitivity of conventional absorbance spectroscopy for chromium(VI) and molybdenum(VI). Analysis of Cr(VI) and Mo(VI) concentrations in water samples with a 5.0 m pathlength liquid core waveguide made of Teflon AF-2400 provided a detection limit for Cr 0.2 and for Mo 0.6 nM. No preconcentration is required in this analysis.

Concentrations of Mo(VI)/nM:

Surface seawater (Gulf of Mexico), 98
Rain water, <0.5
Spring waters (bottled)
Brand # 1,40.0, 39.2
# 2, 41.4, 43.5
# 3, 5,2, 6.8
# 4, 6.0, 5.7
# 5, 260 , 273

Yao, W.S., Byrne, R.H., Determination of trace chromium(VI) and molybdenum(VI) innatural and bottled mineral waters using long pathlengthabsorbance spectroscopy,Talanta, 1999,48,2,277-282.

The detection limit of molybdate in natural waters by coprecipitation and neutron activation analysis was about 1 ng L^-1.

Sun, Y.C., Yang, J.Y., Tzeng, S.R., Rapid determination of molybdate in natural waters by coprecipitation and neutron activation analysis, Analyst, 1999, 124, 3, 421-424.

Eastern Sierra Nevada rivers

Concentration ranges were:
boron 2 mu mol/kg in the upper reaches of the Truckee River to 1,200 mu mol/kg in Pyramid Lake
molybdenum 12 nmol/kg to 3,200 nmol/kg (Walker Lake)
vanadium 9 nmol/kg to 470 nmol/kg
W 0.8 nmol/kg to 1,030 nmol/kg.

The ‘high concentrations’ of these oxyanion-forming trace elements in the rivers reflects the relative stability of the oxyanions in the alkaline, well oxygenated river and lake waters.

Johannesson,K.H., Lyons, B., Graham, E.Y., Welch, K.A., Oxyanion concentrations in eastern Sierra Nevada rivers - 3. Boron, molybdenum, vanadium, and tungsten Aquatic Geochemistry, 2000,6,19-46.

Houston Ship Channel

The molybdenum concentration in the surface water of the Houston ShipChannel determined using inductively coupled plasma/massspectrometry was mu g/L 6.66.

Saleh, M.A., Wilson, B.L., Analysis of metal pollutants in the Houston Ship Channel byinductively coupled plasma/mass spectrometry, Ecotoxicology And Environmental Safety, 1999,44,1,113-117.

Eastern Sierra Nevada rivers

Mo varied from a low of about 12 nmol/kg to a high of 3,200 nmol/kg (Walker Lake).The high concentrations of these oxyanion-forming trace elements in the rivers reflects the relative stability of these oxyanions (e.g., MoO42-, HVO42-, WO42-, B(OH)(3), and/or B(OH)(4)(-)) in the alkaline, well oxygenated river and lake waters, weathering of rocks/regolith with high concentrations of these elements. In the case of Mo, V, and W, each exhibited relatively conservative behaviour in the upper, oxygenated reaches of all three rivers. Reductive processes occurring in the low flow to stagnant reaches of each river (due to a prolonged drought) could have led to removal of Mo, V, and W from solution as coprecipitates with Fe monosulfides, or via sorption to Fe oxides/oxyhydroxides and/or organic matter.

Johannesson, K.H., Lyons, W. B., Graham, E. Y., and Welch, K. A., Oxyanion concentrations in eastern Sierra Nevada rivers - 3. Boron, molybdenum, vanadium, and tungsten, Aquatic Geochemistry, 2000, 6, 19-46.

UK rivers

A series of papers published in Science of the Total Environment, 2000, 251 report data on the water quality of rivers draining into the North Sea from the eastern UK using core information collected within the Land-Ocean Interaction Study (LOIS) and a companion study by the Institute of Hydrology. The analysis is based on weekly monitoring for periods from 1993 to 1999.

Neal, C. and Robson, A. J., A summary of river water quality data collected within the Land-Ocean Interaction Study: core data for eastern UK rivers draining to the North Sea, , 585-665.

In the River Trent acid available Mo in particulates in microg/l was: non tidal, 0.05; freshwater tidal, 0.06 to 0.02 at different locations. Dissolved Mo was 6.51 - 9.28.

Jarvie, H.P., Neal, C., Burton, J. D., and Tappin, A. D., Patterns in trace element chemistry in the freshwater tidal reaches of the River Trent, Science of the Total Environment, 2000, 251, 317-333.

In the River Thames 34 km downstream of Oxford average dissolved Mo was 35.1 microg/l with a maximum of 1588 microg/l (due probably to point source pollutant inputs from light industry).

Neal, C., Williams, R. J., Neal, M., Bhardwaj, L. C., Wickham, H., Harrow, M., and Hill, L. K., The water quality of the River Thames at a rural site downstream of Oxford, Science of the Total Environment, 2000, 251, 441-457.

Trace metal pollution of Tsurumi River, Yokohama, Japan

the trace metal pollution of water and sediments downstream of Tsurumi River, Yokohama, Japan was studied. Twenty samples of water and sediments were collected from the river starting from Tokyo bay side up to the junction point of the Yagami River. The mean concentrations of chromium, cupper and nickel in water greatly exceeded (>100 times) the surface water standard. The concentration of molybdenum and lead was also higher than standard values; iron and manganese were lower than that of surface water standard. The mean concentration of zinc, cupper, cadmium, lead, chromium, vanadium, bromine and iodine was 381.1, 133.0, 1.0, 40.8, 102.9, 162.0, 71.5 and 10.6 microg/g sediments greatly exceeded the average worldwide shale concentrations and average Japanese river sediment values. Mean concentrations of arsenic, nickel and strontium were 11.0, 36.6 and 164.6 microg/g sediments, lower than the average shale value. Other analyzed trace metals, including barium, zirconium, rubidium, yttrium, tin, antimony, cesium, lanthanum, cerium, praseodymium and neodymium were detected in river sediments; their concentration was close to the Japan's river sediment average values. Pollution load index (PLI) values of the sites were from 1.24 to 7.65 showing that the river sediments are polluted. The PLI value of the area was high (6.53) as the concentration of trace metals like zinc, cupper, cadmium, lead and chromium were very high and were the major pollutants

Mohiuddin, K. M., Zakir, H. M., Otomo, K., Sharmin, S., and Shikazono, N., Geochemical distribution of trace metal pollutants in water and sediments of downstream of an urban river, International Journal of Environmental Science and Technology, 2010, 7, 17-28.

Water Sediment-Water Interface

Laguna Caren is a small shallow freshwater system located 20 km from downtown Santiago, Chile. Diffusive fluxes through the sediment-water interface were measured by diffusive dialysis. Dissolved Fe and Mn showed decreasing concentrations from -6.0 cm to 0.0 cm, while concentrations of Mo and Sb increased at this depth. Soluble species of Fe(II) and Mn are available by diffusive transport to the overlying waters, whereas Mo and Sb species are not available in this zone. The fluxes were (in pmol cm^-2 s^-1): Fe(II): 0.05; Mn: 0.28; Mo: -1.2 x 10^-4; Sb: -3.9 x 10^-4

Pizarro, J., Rubio, M. A., and Matta, A., Difussion of Fe, Mn, Mo and Sb in the Sediment-Water Interface of A Shallow Lake, Laguna Caren, Santiago (Chile), Fresenius Environmental Bulletin, 2009, 18, 2336-2344.

A novel combination of magnetic adsorptive and coagulative strategy which was applied to remove molybdenum (Mo) ions from surface water was investigated in this study. The ferromagnetic nanoclusters and ferromagnetic nanoclusters-ferric flocs composite coagulant were characterized in terms of typical properties, structure and morphological analysis (TEM, XRD, M-H hysteresis curves, particle size distribution). Different removal agents of Mo was investigated that the removal rate of Mo was ferromagnetic nanoclusters-FeCl₃ > FeCl₃ >AlCl₃ >TiCl₄. Jar tests were employed to evaluate the removal performances. The coagulation performances of ferromagnetic nanoclusters-ferric flocs were compared under different pH conditions and dosages. Various factors influencing the removal of Mo(VI), e.g. pH, the dose of ferromagnetic nanoparticle, FeCl₃, were conducted using a 3(3) full factorial design approach. The results show that the newly addition of ferromagnetic nanoparticles obviously had a trend to form cluster, especially magnetic force acted as a key role that may promote the formation of ferromagnetic nanoclusters. The better removal performance of Mo could be attributed to the co-effect of ferromagnetic nanoclusters and ferric flocs. Meanwhile, in order to satisfy the national drinking water criterion, the reinforce effect of ferromagnetic nanoclusters on reducing the concentration of ferric (Fe) ions in effluent makes sure that the content of ferric ions under 0.3 mg/L. The experimental results indicated that mechanism of the molybdate removal was a physical surface adsorption which might combine with chemical action. (C) 2015 Elsevier B.V. All rights reserved.

Ma, W., Sha, X. L., Gao, L. L., Cheng, Z. H., Meng, F. Q., Cai, J., Tan, D. Z., and Wang, R.,Effect of iron oxide nanocluster on enhanced removal of molybdate from surface water and pilot scale test, Colloids and Surfaces a-Physicochemical and Engineering Aspects, 2015, 478, 45.

Molybdenum (Mo) content was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to evaluate suitability for land application under state regulatory policies that limit Mo to 18 mg kg(-1). Samples of of water treatment residuals were collected from 32 Pennsylvania facilities that employ aluminium salts, ferric chloride, and/or polymers for coagulation. Mean Mo content of all samples was 3.1 mg kg-1.
The water treatment residuals from plants using ferric chloride as a coagulant averaged 5.6 mg Mo kg-1
1.6 mg Mo kg-1 for utilities using alum.
Differences were related to coagulant purity: Mo content in liquid ferric chloride nas 10.0 mg L^-1 but below detection by ICP-AES for alum.
The mean Cu to Mo ratio in these water treatment residuals was >100, well above the minimum dietary ratio (2:1) considered protective of grazing animals

Elliott, H.A. and Taylor, M., Molybdenum content of water treatment residuals, Journal of Environmental Quality, 2000, 29, 1835-1839.

Metal contamination of freshwater ecosystems is increasingly prevalent due to anthropogenic activities such as metal smelting and fossil fuel combustion. Cladoceran diapausing eggs (ephippia), which are abundant in nature and accumulate maternally derived metals, can be used to measure historical variations in biologically relevant metals that derive from the water column ( water, diet). Metals were incorporated into ephippia with little contamination from the sediment matrix. Some metals associated with urban sources (Cd, Cr, Mo) were preferentially concentrated in ephippia, whereas concentrations of other metals indicating landscape erosion (Al, Ca, Fe, Mn) exhibited greater concentrations in bulk sediments than in diapausing eggs. Past variation in the metal content of ephippia provided a unique history of food web exposure to metals in the water column

Wyn, B., Sweetman, J. N., Leavitt, P. R., and Donald, D. B., Historical metal concentrations in lacustrine food webs revealed using fossil ephippia from Daphnia, Ecological Applications, 2007, 17, 754-764.

We measured potential rates of bacterial dissimilatory reduction of ⁷⁵SeO₄²⁻ to ⁷⁵Se⁰ in a diversity of sediment types, with salinities ranging from freshwater (salinity = 1 g/liter) to hypersaline (salinity = 320 g/liter and with pH values ranging from 7.1 to 9.8. Significant biological selenate reduction occurred in all samples with salinities from 1 to 250 g/liter but not in samples with a salinity of 320 g/liter. Potential selenate reduction rates (25 nmol of SeO₄²⁻ per ml of sediment added with isotope) ranged from 0.07 to 22 μmol of SeO₄²⁻ reduced liter⁻¹ h⁻¹. Activity followed Michaelis-Menten kinetics in relation to SeO₄²⁻ concentration (K_m of selenate = 7.9 to 720 μM). There was no linear correlation between potential rates of SeO₄²⁻ reduction and salinity, pH, concentrations of total Se, porosity, or organic carbon in the sediments. However, potential selenate reduction was correlated with apparent K_m for selenate and with potential rates of denitrification (r = 0.92 and 0.81, respectively). NO₃⁻, NO₂⁻, MoO₄²⁻, and WO₄²⁻ inhibited selenate reduction activity to different extents in sediments from both Hunter Drain and Massie Slough, Nev. Sulfate partially inhibited activity in sediment from freshwater (salinity = 1 g/liter) Massie Slough samples but not from the saline (salinity = 60 g/liter) Hunter Drain samples. We conclude that dissimilatory selenate reduction in sediments is widespread in nature. In addition, in situ selenate reduction is a first-order reaction, because the ambient concentrations of selenium oxyanions in the sediments were orders of magnitude less than their K_ms.

Dissimilatory Selenate Reduction Potentials in a Diversity of Sediment Types Nisan A. Steinberg and Ronald S. Oremland, Appl Environ Microbiol. 1990, 56,3550-7.

Mo in seawater collected from Salvador City, Bahia, Brazil. was determined by using atomic emission spectrometry with inductively coupled plasma (ICP-AES).after preconcentration (100) of Mo on activated carbon. Mo concentrations in seawater from 4 locations were: 7.9 +/- 0.9, 8.5 +/- 0.5, 8.0 +/- 0.7, 8.4 +/- 0.1 microg l^-1.

dos Santos, H.C., Korn, M. G. A., and Ferreira, S. L. C., Enrichment and determination of molybdenum in geological samples and seawater by ICP-AES using calmagite and activated carbon, Analytica Chimica Acta, 2001, 426, 79-84.
Firdaus, M. L., Norisuye, K., Nakagawa, Y., Nakatsuka, S., and Sohrin, Y., Dissolved and labile particulate Zr, Hf, Nb, Ta, Mo and W in the western North Pacific Ocean, Journal of Oceanography, 2008, 64, 247-257.

Isotopic Analysis of molybdenum in seawater

The ocean is a reservoir of molybdenum. The natural isotopic variation of molybdenum tells us about the geochemical circulation of molybdenum. A preconcentration technique using 8-hydroxyquinoline bonded covalently to a vinyl polymer resin (TSK-8HQ) was developed and enabled molybdenum in seawater to be separated from matrix elements, alkali, alkaline earth, and transition metals. An accurate ratio for every pair of stable molybdenum isotopes was then determined using multiple collector-inductively coupled plasma mass spectrometiy (MC-ICPMS),.

Four kinds of seawater samples were analysed. The molybdenum compositions were constant among them, with average delta(98)/molybdenum-95 and delta(92)/molybdenum-98 values of 2.45 ± 0.11 and -4.94 ± 0.09 parts per thousand (± 2 SD). Seawater is more enriched in heavy molybdenum isotopes than previously reported.

Nakagawa, Y., Firdaus, M. L., Norisuye, K., Sohrin, Y., Irisawa, K., and Hirata, T., Precise Isotopic Analysis of Mo in Seawater Using Multiple Collector-Inductively Coupled Mass Spectrometry Coupled with a Chelating Resin Column Preconcentration Method, Analytical Chemistry, 2008, 80, 9213-9219.

Water sea Mo isotopic composition in sedimentsChesapeake Bay

Manganese oxyhydroxides (MnO_x) are a major sink for molybdate in oxygenated seawater. Molybdate adsorbed onto MnO_x is isotopically light relative to dissolved MoO₄²⁻ in the source solution

Fractionation of molybdenum isotopes during adsorption to MnO_x is primarily responsible for the heavy isotopic composition of seawater Dissolved molybdenum in seawater present almost entirely as MoO₄²⁻ has an isotopic composition (δ⁹⁸Mo) as much as two parts per thousand (2‰) heavier than molybdenum delivered from continental sources, such as clastic sediments and igneous rocks.

However, authigenic molybdenum deposited in suboxic environments is also 1 to 2‰ lighter than seawater. Since MnO_x is not deposited under suboxic conditions, at least one additional process for selectively removing light molybdenum isotopes from seawater must exist. A second process that might influence δ⁹⁸Mo values in sediments from suboxic zones is fractionation during thiomolybdate formation.

This process probably contributes to the modern, heavy δ⁹⁸Mo value of seawater, and will have contributed to past seawater δ⁹⁸Mo values.

Molybdenum isotope data for sediments and waters of the seasonally anoxic Chesapeake Bay, and its primary tributary, the Susquehanna River were measured.

Scheiderich, K., Helz, G. R., and Walker, R. J., Century-long record of Mo isotopic composition in sediments of a seasonally anoxic estuary (Chesapeake Bay), Earth and Planetary Science Letters, 2010, 289, 189-197.

[Background: Authigenic : descriptive of rock constituents and minerals which are formed or generated in the location where they are found;materials usually are formed subsequent to deposition, but might be formed at the time of deposition.

Quantum mechanical calculation of the binding differences of different molybdenum isotopes.

Isotopic fractionation equilibrium constants for exchange of light and heavy molybdenum isotopes between the molybdate species dominant in seawater and a range of oxidic and sulfidic molybdenum species were calculated from the difference in the vibrational, rotational and translational contributions to the free energy in the gas phase for the gas-phase reaction involving different isotopomers with different molybdenum isotopes. This requires calculationofthe equilibrium geometries and vibrational freqencies for all the species involved. The different isotopomers of these species will have the same force constants within the standard Born-Oppenheimer approximation, but their vibrational frequencies will be different for those vibrations involving molybdenum motion since such vibrational normal modes will have different reduced masses.

J. A. Tossell, Geochimica et Cosmochimica Acta, 69, 2981–2993, 2005: Calculating the partitioning of the isotopes of Mo between oxidic and sulfidic species in aqueous solution].

Sediments metal distribution Gulf of Finland

This study is the first of its kind, as a systematic mapping of the whole coastal area of the Finnish part of the Gulf of Finland. This area was sampled with a relatively even spacing and the distributions of heavy metals and arsenic in the modem soft surface sediments are presented as circular symbol maps. Data on cobalt and molybdenum are reported for the first time from a total digestion from samples from this area. The sediments are strongly enriched by some of the studied elements due to the anthropogenic load, while others are only moderately present. High or relatively high levels of cadmium, copper, mercury, molybdenum, and zinc were found in the easternmost part of the study area

Vallius, H., Heavy metal distribution in the modern soft surface sediments off the Finnish coast of the Gulf of Finland, Baltica, 2009, 22, 65-76.

Water sea molybdenum enrichment in scallop shells in temperate coastal environments

Skeletal molybdenum/calcium ([Mo]/[Ca])(shell) ratios were examined in shells of the Great Scallop Pecten maximus collected in temperate coastal environments of Western Europe (42 to 49 degrees N). Variations of ([Mo]/[Ca])(shell) ratios were significant and reproducible for scallops from the same population, from different years (1998-2004) and temperate coastal locations (NW France). Both the intense monitoring survey in 2000 and over the 7-year period indicates that the ([Mo]/[Ca])(shell) maximum is directly influenced by spring changes of environmental conditions at the sediment water interface, occurring subsequent to the intense and periodic spring bloom. Spring maxima of ([Mo]/[Ca])(shell) ratios are closely correlated to the extent of silicic acid and nitrate depletion in seawater between winter and late spring that reflects diatom uptake and productivity in the Bay of Brest. The [Mo]/[Ca])(shell) records thus reveal unexpected biogeochemical cycles of Mo influenced by coastal spring productivity, faithfully recorded in scallop shells

Barats, A., Amouroux, D., Pecheyran, C., Chauvaud, L., Thebault, J., and Donard, O. F. X., Spring molybdenum enrichment in scallop shells: a potential tracer of diatom productivity in temperate coastal environments (Brittany, NW France), Biogeosciences, 2010, 7, 233-245.

Co, Cr, Mo, and Sb have been measured by DF-ICP-MS-MCN (double focusing inductively coupled plasma mass spectrometry with microconcentric nebulizer) in various sections of a 140 m snow/ice core drilled at a high altitude location near the summit of Mont Blanc in the French-Italian Alps. The bottom of the core is older than 200 years. Concentrations in recent snow are higher than concentrations in ice dated from before the middle of the 19^th century Mo shows the greatest increase (x16), followed by Sb (x5), and Co and Cr (x2-3) For recent snow, contribution from oil and coal combustion is the dominating source for Co, Mo,and Sb. For Cr, on the other hand, the most important contribution is from iron, steel, and ferroalloy industries.

Mo 0.2 - 50 pg/g
Co 26 - 433 pg/g
Cr 8 - 469pg/g
Sb 0.2 - 109 pg/g

VandeVelde, K., Ferrari, C., Barbante, C., Moret, I., Bellomi, T., Hong, S.M., Boutron, C., A 200 year record of atmospheric cobalt, chromium, molybdenum,and antimony in high altitude alpine firn and ice, Environmental Science & Technology, 1999,33,3495-3501

Application of Groundwater Thresholds for Trace Elements on Percolation Water: A Case Study on Percolation Water from Northern German Lowlands

The German insignificance thresholds (GFS) for groundwater, derived with an added risk approach, will soon be adopted as trigger values for percolation water entering groundwater. The physicochemical properties of the vadose zone differ considerably from those of groundwater, which may lead to difficulties in the applicability of groundwater-derived GFS to percolation water. To test the applicability of the GFS to percolation water regarding the concentration level and the field-scale variability, 46 sites in Northern Germany were sampled, including arable land, grassland, and forest, situated on three spatially dominant parent materials: sand, glacial loam, and loess. Concentrations of As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Sn, V, Zn, and F were analyzed in percolation water from the transition between the unsaturated to the saturated zone. We compared median and 90th percentile values of the background concentrations with the GFS. In more than 10% of all samples, background concentrations of Cd, Co, Ni, V, or Zn exceeded the GFS. We evaluated the applicability of the GFS on field-scale medians of background concentrations taking field-scale interquartile distance and the bootstrap percentile confidence interval of the field scale median of trace element background concentrations into consideration. Statements about exceedance or nonexceedance of GFS values could only be made with acceptable statistical uncertainty (alpha <= 0.1) when operational median concentrations were about one third higher or lower than the corresponding GFS

Godbersen, L., Duijnisveld, W. H. M., Utermann, J., Gaebler, H. E., Kuhnt, G., and Boettcher, J., Application of Groundwater Thresholds for Trace Elements on Percolation Water: A Case Study on Percolation Water from Northern German Lowlands, Journal of Environmental Quality, 2012, 41, 1253-1262.

Submarine groundwater discharge (SGD) is an important component of chemical fluxes in the coastal ocean. The composition of SGD is influenced by biogeochemical reactions that take place within the subterranean estuary (STE), the subsurface mixing zone of fresh and saline groundwaters. The STE is characterized by redox gradients that affect the speciation and mobility of redox-sensitive elements (RSEs). We examined the distributions and behavior of the RSEs Mo, U, V, and Cr within the larger redox framework of a shallow STE and evaluated the source-sink function of the STE for these elements. We found that the advection of water through the STE and the apparent respiration of organic matter drives the formation of a "classic" redox sequence typically observed in diffusion-dominated fine-grained sediments. High concentrations of dissolved organic matter (up to 2.9 mM) lead to extensive sulfide production (up to 1.8 mM) within 3 m of the surface. Both Mo and U are quantitatively removed as oxic surface waters mix into ferruginous and sulfidic zones. Molybdenum removal appears to occur where sulfide concentrations exceed similar to 11 mu M, a previously reported threshold for quantitative formation of highly particle-reactive thiomolybdate species. Uranium removal apparently occurs via reduction and formation of insoluble phases or sorption to sediments. It is not clear how readily sequestered metals may be returned to solution, but SGD may be an important sink in the marine budget for both Mo and U. In contrast, both V and Cr show non-conservative addition across the salinity mixing gradient. Increases in pH appear to promote dissolution of V from minerals within the shallow aquifer, and mobilization may also be associated with dissolved organic matter. Chromium enrichment is associated with higher dissolved organic matter and is likely due to the formation of soluble Cr-organic complexes. Fluxes of these elements were constrained using SGD volume fluxes, determined using radium isotopes as well as direct discharge measurements by Lee-type seepage meters, and concentrations in directly-sampled seepage (Mo: -0.21 to -7.7 mu mol m(-2) day(-1); U: -0.02 to -0.6 mu mol m(-2) day(-1); V: 0.05 to 2.0 mu mol m(-2) day(-1); Cr: 0.12 to 4.4 mu mol m(-2) day(-1)). (C) 2015 Elsevier B.V. All rights reserved.

O'Connor, A. E., Luek, J. L., McIntosh, H., and Beck, A. J.,Geochemistry of redox-sensitive trace elements in a shallow subterranean estuary, Marine Chemistry, 2015, 172, 70.

Two hundred and three groundwater samples were collected during March 2011 to June 2012 from the B2/A7 aquifer water supply wells of northern part of Jordan. The physicochemical properties were analyzed in situ for the major cations, anions, while certain heavy metals were analyzed in the laboratory. Some oilshale rock samples were geochemically analyzed. The Upper Cretaceous aquifer (B2/A7) is used as water supply for most of the communities in the study area. It consists of limestone, marly limestone, bedded chert, and minor phosphorite. Hydrochemical results from the B2/A7 aquifer indicate two main water types: alkaline-earth water (CaHCO₃) and alkaline-earth water with high alkaline component (NaHCO₃ , Na₂SO₄). Standard column leaching experiments on oilshale rock samples and the R-mode factor analysis suggest that the sources for elevated Mo concentrations in the groundwater of certain parts of northern Jordan are attributed to water-oilshale interaction, mobility of Mo down to the groundwater and the extensive use of fertilizers within these areas. Molybdenum (Mo) concentrations in the groundwater water range from 0.07 to 1.44 mg/L with an average value of 98 ?g/L. They are found to exceed the JISM and WHO guidelines in two areas in northern part of Jordan. Spatial distribution of Mo, using ordinary kriging techniques and the resulting map, shows high Mo concentration in the northwestern part near Wadi Al Arab area reaching concentrations of 650 ?g/L and in the southeastern corner of the investigated area, south of Al Ukaydir village, with an average concentration of 468 ?g/L. Both areas are characterized by extensive oilshale exposures with average concentration of 11.7 mg/kg Mo and intensive agricultural activities. These two areas represent approximately 33 % of the groundwater in the northern part of Jordan. Mobility of Mo to the groundwater in northern part of Jordan is attributed to two mechanisms. First, there is reductive dissolution of Fe-oxide, which releases substantial adsorbed Mo concentrations. Secondly, there is oxidation of Mo into dissolved forms in sulfide organic-rich system.

Al Kuisi M, Al-Hwaiti M, Mashal K, Abed AM. Spatial distribution patterns of molybdenum (Mo) concentrations in potable groundwater in Northern Jordan. . Environ Monit Assess. 2015 Mar;187(3):4264. doi: 10.1007/s10661-015-4264-5. Epub 2015 Feb 27.

The role of wetlands in the retention or release of trace elements to streams was investigated. Temporal and spatial patterns of concentrations of trace elements were determined by ICP-MS and geochemical drivers in five streams and wetland rivulets draining natural wetlands in a northern Wisconsin watershed and in their groundwater sources (terrestrial recharge, lake recharge, and older lake recharge). The low levels Cu and Mo in the rivulets were attributed to redox cycling and precipitation and dissolution reactions involving Fe and Mn.Variance in Fe, Mn and the metal oxy-anions was associated with redox cycling and adsorption reactions in the wetland sediments

A wetland is an area of land consisting of soil that is saturated with moisture, such as a swamp, marsh, or bog. Some of the time water saturates the soil; the result is a hydric soil, one characterized by an absence of free oxygen some or all of the time, and therefore called a "reducing environment. (Wikipedia).

Kerr, S. C., Shafer, M. M., Overdier, J., and Armstrong, D. E., Hydrologic and biogeochemical controls on trace element export from northern Wisconsin wetlands, Biogeochemistry, 2008, 89, 273-294.

Considering the increasing pace of global land use change and the importance of groundwater quality to humans and aquatic ecosystems, studies are needed that relate land use types to patterns of groundwater chemical composition. Piezometer grids were installed in a remnant bottomland hardwood forest (BHF) and a historic agricultural field (Ag) to compare groundwater chemical composition between sites with contrasting land use histories. Groundwater was sampled monthly from June 2011 to June 2013, and analyzed for 50 physiochemical metrics. Statistical tests indicated significant differences (p<0.05) between the study sites for 32 out of 50 parameters. Compared to the Ag site, BHF groundwater was characterized by significantly (p<0.05) lower pH, higher electrical conductivity, and higher concentrations of total dissolved solids and inorganic carbon. BHF groundwater contained significantly (p<0.05) higher concentrations of all nitrogen species except nitrate, which was higher in Ag groundwater. BHF groundwater contained significantly (p<0.05) higher concentrations of nutrients such as sulfur, potassium, magnesium, calcium, and sodium, relative to the Ag site. Ag groundwater was characterized by significantly (p<0.05) higher concentrations of trace elements such as arsenic, cadmium, cobalt, copper, molybdenum, nickel, and titanium. Comparison of shallow groundwater chemical composition with that of nearby receiving water suggests that subsurface concentration patterns are the result of contrasting site hydrology and vegetation. Results detail impacts of surface vegetation alteration on subsurface chemistry and groundwater quality, thereby illustrating land use impacts on the lithosphere and hydrosphere. This study is among the first to comprehensively characterize and compare shallow groundwater chemical composition at sites with contrasting land use histories.

Kellner, E., Hubbart, J. A., and Ikem, A.,A comparison of forest and agricultural shallow groundwater chemical status a century after land use change, Sci Total Environ, 2015, 529, 82.

Biomass of Phragmites australis growing in four constructed wetlands with horizontal subsurface flow (HF CWs) designed for treatment of municipal sewage in the Czech Republic have been analyzed for 19 trace elements. The biomass was harvested during the peak standing crop in early September and divided into stems, leaves, flowers, roots and rhizomes. Concentrations of elements in both aboveground and belowground plant tissues were similar to those found in plants growing in natural stands. The highest concentrations were Al, Fe, Mn, Ba and Zn and the lowest concentrations were Hg, U and Cd. Concentrations decreased roots > rhizomes > leaves > stems. The root/leaf ratio averaged 70 and varied between 1.4 for molybdenum and 392 for cobalt. The belowground/aboveground concentration ratio ranged between 0.9 and 69.5 with an average value of 19. Due to average aboveground/belowground biomass ratio > 1, the belowground/aboveground standing stock ratios were lower with six elements (Ba, Zn, Se, Hg, Mo, and Mn) having this ratio < 1.

Vymazal, J., Kropfelova, L., Svehla, J., Chrastny, V., and Stichova, J., Trace elements in Phragmites australis growing in constructed wetlands for treatment of municipal wastewater, Ecological Engineering, 2009, 35, 303-309.

Molybdenum (Mo) is an essential micronutrient for biological assimilation of nitrogen gas and nitrate because it is present in the cofactors of nitrogenase and nitrate reductase enzymes. Although Mo is the most abundant transition metal in seawater (107 nM), it is present in low concentrations in most freshwaters, typically . In 1960, it was discovered that primary productivity was limited by Mo scarcity (2-4 nM) in Castle Lake, a small, meso-oligotrophic lake in northern California. Follow up studies demonstrated that Mo also limited primary productivity in lakes in New Zealand, Alaska, and the Sierra Nevada. Research in the 1970s and 1980s showed that Mo limited primary productivity and nitrate uptake in Castle Lake only during periods of the growing season when nitrate concentrations were relatively high because ammonium assimilation does not require Mo. In the years since, research has shifted to investigate whether Mo limitation also occurs in marine and soil environments. Here we review studies of Mo limitation of nitrogen assimilation in natural microbial communities and pure cultures. We also summarize new data showing that the simultaneous addition of Mo and nitrate causes increased activity of proteins involved in nitrogen assimilation in the hypolimnion of Castle Lake when ammonium is scarce. Furthermore, we suggest that meter-scale Mo and oxygen depth profiles from Castle Lake are consistent with the hypothesis that nitrogen-fixing cyanobacteria in freshwater periphyton communities have higher Mo requirements than other microbial communities. Finally, we present topics for future research related to Mo bioavailability through time and with changing oxidation state

Glass, Jennifer B., Axler, Richard P., Chandra, Sudeep, and Goldman, Charles R., Molybdenum limitation of microbial nitrogen assimilation in aquatic ecosystems and pure cultures, Frontiers in microbiology, 2012, 3, 331.

In a regulatory context, bioaccumulation or bioconcentration factors are used for considering secondary poisoning potential and assessing risks to human health via the food chain. In this paper, literature data on the bioaccumulation of molybdenum in the aquatic organisms are reviewed and assessed for relevance and reliability. The data available in the literature were generated at exposure concentrations below those recommended in the REACH registration dossiers for molybdenum compounds i.e. PNEC(freshwater) 12.7mg Mo/L. To address possible environmental concerns at regulatorily-relevant molybdenum concentrations, both a field study and a laboratory study were conducted. In the field study, whole body and organ-specific molybdenum levels were evaluated in fish (eel, stickleback, perch, carp bream, roach) held in the discharge water collector tanks of a molybdenum processing plant, containing a mean measured molybdenum level of 1.03mg Mo/L. In the laboratory study, rainbow trout were exposed to two different nominal molybdenum levels (1.0 and 12.7mg Mo/L), for 60days followed by a 60-day depuration period. Whole body concentrations in rainbow trout during the exposure period were between <0.20 and 0.53mg Mo/L. Muscle tissue molybdenum concentrations in fish taken from both experiments remained below 0.2mg/kg dry wt. These studies show an inverse relationship between exposure concentration and bioconcentration or bioaccumulation factor for molybdenum. In aquatic organisms, and in fish in particular, internal molybdenum concentrations are maintained in the presence of variation in external molybdenum concentrations. These observations must be considered when evaluating potential risks associated with the bioconcentration and/or bioaccumulation of molybdenum in the aquatic environment

Regoli, Lidia, Van Tilborg, Wim, Heijerick, Dagobert, Stubblefield, William, and Carey, Sandra, The bioconcentration and bioaccumulation factors for molybdenum in the aquatic environment from natural environmental concentrations up to the toxicity boundary, The Science of the total environment, 2012, 435-436, 96-106.

The chronic toxicity of molybdate to marine organisms. I. Generating reliable effects data

A scientific research program was initiated by the International Molybdenum Association (IMOA) which addressed identified gaps in the environmental toxicity data for the molybdate ion (MoO₄^2-). These gaps were previously identified during the preparation of EU-REACH-dossiers for different molybdenum compounds (European Union regulation on Registration, Evaluation, Authorization and Restriction of Chemical substances; EC, 2006). Evaluation of the open literature identified few reliable marine ecotoxicological data that could be used for deriving a Predicted No-Effect Concentration (PNEC) for the marine environment. Rather than calculating a PNEC(marine) using the assessment factor methodology on a combined freshwater/marine dataset, IMOA decided to generate sufficient reliable marine chronic data to permit derivation of a PNEC by means of the more scientifically robust species sensitivity distribution (SSD) approach (also called the statistical extrapolation approach). Nine test species were chronically exposed to molybdate (added as sodium molybdate dihydrate, Na₂MoO₄.2H₂O) according to published standard testing guidelines that are acceptable for a broad range of regulatory purposes. The selected test organisms were representative for typical marine trophic levels: micro-algae/diatom (Phaeodactylum tricornutum, Dunaliella tertiolecta), macro-alga (Ceramium tenuicorne), mysids (Americamysis bahia), copepod (Acartia tonsa), fish (Cyprinodon variegatus), echinoderms (Dendraster exentricus, Strongylocentrotus purpuratus) and molluscs (Mytilus edulis, Crassostrea gigas). Available NOEC/EC(10) levels ranged between 4.4mgMo/L (blue mussel M. edulis) and 1174mgMo/L (oyster C. gigas). Using all available reliable marine chronic effects data that are currently available, a HC(5,50%) (median hazardous concentration affecting 5% of the species) of 5.74(mgMo)/L was derived with the statistical extrapolation approach, a value that can be used for national and international regulatory purposes.

Heijerick, D. G., Regoli, L., and Stubblefield, W., The chronic toxicity of molybdate to marine organisms. I. Generating reliable effects data, The Science of the total environment, 2012, 430, 260-269.