AQUATIC

Interactions of monolayer molybdenum disulfide sheets with metalloid antimony in aquatic environment: Adsorption, transformation, and joint toxicity

The tremendous application potentiality of transitional metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) nanosheets, will unavoidably lead to increasing release into the environment, which could influence the fate and toxicity of co-existed contaminants. The present study discovered that 59.8 % of trivalent antimony [Sb(III)] was transformed by to pentavalent Sb [Sb(V)] in aqueous solutions under light illumination, which was due to hole oxidation on the nanosheet surfaces. A synergistic toxicity between MoS2 and Sb(III, V) to algae (Chlorella vulgaris) was observed, as demonstrated by the lower median-effect concentrations of MoS2+ Sb(III)/Sb(V) (13.1 and 20.9 mg/L, respectively) than Sb(III)/Sb(V) (38.8 and 92.5 mg/L, respectively) alone. Particularly, MoS2 at noncytotoxic doses notably increased the bioaccumulation of Sb(III, V) in algae, causing aggravated oxidative damage, photosynthetic inhibition, and structural alterations. Metabolomics indicated that oxidative stress and membrane permeabilization were primarily associated with down-regulated amino acids involved in glutathione biosynthesis and unsaturated fatty acids. MoS2 co-exposure remarkably decreased the levels of thiol antidotes (glutathione and phytochelatins) and aggravated the inhibition on energy metabolism and ATP synthesis, compromising the Sb(III, V) detoxification and efflux. Additionally, extracellular P was captured by the nanosheets, also contributing to the uptake of Sb(V). Our findings emphasized the nonignorability of TMDs even at environmental levels in affecting the ecological hazard of metalloids, providing insight into comprehensive safety assessment of TMDs.

Zou, Y. Zhang, X. Zhang, G. Zhang, X. Li, C. Jin, and Z. Cao,Interactions of monolayer molybdenum disulfide sheets with metalloid antimony in aquatic environment: Adsorption, transformation, and joint toxicity, Sci Total Environ, 2024, 926, 171937.

ENVIRONMENT

AQUATIC

Interactions of monolayer molybdenum disulfide sheets with metalloid antimony in aquatic environment: Adsorption, transformation, and joint toxicity

The tremendous application potentiality of transitional metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS₂) nanosheets, will unavoidably lead to increasing release into the environment, which could influence the fate and toxicity of co-existed contaminants. The present study discovered that 59.8 % of trivalent antimony [Sb(III)] was transformed by to pentavalent Sb [Sb(V)] in aqueous solutions under light illumination, which was due to hole oxidation on the nanosheet surfaces. A synergistic toxicity between MoS₂ and Sb(III, V) to algae (Chlorella vulgaris) was observed, as demonstrated by the lower median-effect concentrations of MoS₂+ Sb(III)/Sb(V) (13.1 and 20.9 mg/L, respectively) than Sb(III)/Sb(V) (38.8 and 92.5 mg/L, respectively) alone. Particularly, MoS₂ at noncytotoxic doses notably increased the bioaccumulation of Sb(III, V) in algae, causing aggravated oxidative damage, photosynthetic inhibition, and structural alterations. Metabolomics indicated that oxidative stress and membrane permeabilization were primarily associated with down-regulated amino acids involved in glutathione biosynthesis and unsaturated fatty acids. MoS₂ co-exposure remarkably decreased the levels of thiol antidotes (glutathione and phytochelatins) and aggravated the inhibition on energy metabolism and ATP synthesis, compromising the Sb(III, V) detoxification and efflux. Additionally, extracellular P was captured by the nanosheets, also contributing to the uptake of Sb(V). Our findings emphasized the nonignorability of TMDs even at environmental levels in affecting the ecological hazard of metalloids, providing insight into comprehensive safety assessment of TMDs.

Zou, Y. Zhang, X. Zhang, G. Zhang, X. Li, C. Jin, and Z. Cao,Interactions of monolayer molybdenum disulfide sheets with metalloid antimony in aquatic environment: Adsorption, transformation, and joint toxicity, Sci Total Environ, 2024, 926, 171937.

BIOACCUMULATION

Bioaccumulation of molybdate ions by alkanotrophic Rhodococcus leads to significant alterations in cellular ultrastructure and physiology

Alkanotrophic Rhodococcus strains from the Regional Specialised Collection of Alkanotrophic Microorganisms (acronym IEGM, www.iegmcol.ru) were screened for accumulation and sorption of MoO₄^2- ions. Morphological and ultrastructural changes observed in bacterial cells during their cultivation in the molybdenum-containing medium are described. The species peculiarities, growth substrate preferences, and other physiological features allowing for the efficient removal of molybdate ions from the culture medium are discussed. Bioinformatics analysis of genes and proteins responsible for resistance to and accumulation of molybdenum was carried out using the sequenced R. ruber IEGM 231 and other published Rhodococcus genomes. n-Hexadecane growing strains with high (up to 85 %) accumulative activity and resistance to elevated (up to 20.0 mM) molybdenum concentrations were selected, which can be used for bioremediation of environments co-contaminated with heavy metals and hydrocarbons. Transmission electron microscopy and energy dispersive X-ray spectroscopy (TEM-EDX) revealed the ability of Rhodococcus not only to accumulate, but also to chemically convert soluble toxic molybdenum into insoluble compounds detected in the form of electron-dense nanoparticles.

1. B. Ivshina, M. S. Kuyukina, L. V. Litvinenko, A. A. Golysheva, N. A. Kostrikina, V. V. Sorokin, and A. L. Mulyukin,Bioaccumulation of molybdate ions by alkanotrophic Rhodococcus leads to significant alterations in cellular ultrastructure and physiology, Ecotoxicol Environ Saf, 2024, 274, 116190.

SOIL

Deriving ecological risk thresholds for soil molybdenum in China based on interspecies correlation estimation and quantitative ion character-activity relationship models

Soil molybdenum (Mo) levels can reach ecologically hazardous levels. China has not yet established the relevant thresholds, posing challenges for environmental management. Therefore, we present our data relevant to Mo toxicity for several important species. By normalizing soil properties, we obtained a correlation model of Mo toxicity to Hordeum vulgare, as well as 31 models for the toxicity of other elements including Cu and Ni to invertebrates and microbial processes. Using interspecies correlation estimation (ICE) extrapolation, the sensitivity coefficient (0.12-0.71) for five plants were found. For invertebrates and microbial processes lacking Mo data, we used regression analysis to establish Mo toxicity models based on the soil quantitative ion character-activity relationships (s-QICAR; R(2) =0.70-0.95) and known toxicities of other metal elements to invertebrate and microbial processes. Furthermore, combining species sensitivity distribution calculations, the HC(5) values for protecting 95% of soil species from Mo in three typical soil scenarios in China were calculated. After correction, the predicted no-effect concentrations were 6.8, 4.8, and 3.4 mg/kg, respectively. This study innovatively combined ICE and s - QICAR to derive soil Mo thresholds. Our results can provide a basis for decision-making in the assessment and management of soil Mo pollution.

Shi, X. Wang, T. Xia, X. Pu, and J. Bian,Deriving ecological risk thresholds for soil molybdenum in China based on interspecies correlation estimation and quantitative ion character-activity relationship models, J Hazard Mater, 2024, 472, 134483.

Molybdenum-mediated nitrogen accumulation and assimilation in legumes stepwise boosted by the coexistence of arbuscular mycorrhizal fungi and earthworms

Molybdenum (Mo) is a critical micronutrient for nitrogen (N) metabolism in legumes, yet the impact of Mo on legume N metabolism in the context of natural coexistence with soil microorganisms remains poorly understood. This study investigated the dose-dependent effect of Mo on soil N biogeochemical cycling, N accumulation, and assimilation in alfalfa under conditions simulating the coexistence of arbuscular mycorrhizal fungi (AMF) and earthworms. The findings indicated that Mo exerted a hormetic effect on alfalfa N accumulation, facilitating it at low concentrations (below 29.98 mg/kg) and inhibiting it at higher levels. This inhibition was attributed to Mo-induced constraints on C supply for nitrogen fixation. Concurrently, AMF colonization enhanced C assimilation in Mo-treated alfalfas by promoting nutrients uptake, particularly Mg, which is crucial for chlorophyll synthesis. This effect was further amplified by earthworms, which improved AMF colonization (p < 0.05). In the soil N cycle, these organisms exerted opposing effects: AMF enhanced soil nitrification and earthworms reduced soil nitrate (NO3- (-N) reduction to jointly increase soil phyto-available N content (p < 0.05). Their combined action improved alfalfa N assimilation by restoring the protein synthesis pathway that is compromised by high Mo concentrations, specifically the activity of glutamine synthetase. These findings underscored the potential for soil microorganisms to mitigate N metabolic stress in legumes exposed to elevated Mo levels.

1. Yang, and L. Wang,Molybdenum-mediated nitrogen accumulation and assimilation in legumes stepwise boosted by the coexistence of arbuscular mycorrhizal fungi and earthworms, Sci Total Environ, 2024, 927, 171840.

Evaluation of Heavy Metals in Soil Wastewater Stream

Environmental pollution is one of the main factors that significantly affect biological systems and human health. Soil pollution with heavy metals is an increasingly pressing problem worldwide. In general, heavy metals are stable and do not decompose, unlike other organic pollutants. The quantity of them is natural components of soil crust, the remaining come from human activities, which may result from the extensive use of sewage. In the present study, a methodology aimed at simultaneous quantification of 16 heavy elements in soil of 3 different regions was developed. The concentration of 16 soil heavy metals (Se, Cd, V, Be, As, Mn, Co, Zn, Fe, Cr, Pb, Ni, Cu, Mo, Hg, and Ti) was measured in 11 sampling along Riyadh, Qassim, and Medina, Kingdom of Saudi Arabia from 3 sites soil treated with sewage water. These chemical minerals were identified in the samples using an ICPE-9000 spectrometer. The assessment of heavy metal contamination was derived using enrichment factors (EF), the pollution load index (PLI), and geoaccumulation index (I-geo). This study revealed that the soil is predominantly polluted by Cd, As, and Mo of Riyadh and Medina and As, Mo, and Cd of Qassim region at site B and site C, respectively. As recorded, the highest concentration value of 5000 mg/kg for Fe at site (B) followed by Cu. The I-geo value of Cd is 1.1520 in Medina region. The I-geo value of Se is 3.2395 in Medina region, while its cumulative geographical index decreased in the regions of Riyadh and Qassim, which amounted to 2.6114 and 2.1699, respectively. The I-geo values of the rest of the minerals in the three regions studied indicated that the soil is unpolluted, while it was slightly to moderately polluted for both Mo and Hg in most regions studied. The minerals in the soil at all sites studied were less than the general average concentration. With the exception of mercury, molybdenum, arsenic, cadmium, and selenium, whose concentration exceeded the permissible and recommended limits. The increasing order of concentration of minerals was Be < V < Cd < Hg < Mo < Co < Zn < Pb < Cr < Se < As < Ni < Ti < Mn < Cu < Fe at all sites, respectively.

A. Alnuwaiser,Evaluation of Heavy Metals in Soil Wastewater Stream, International Journal of Analytical Chemistry, 2022, 2022.

Naturally occurring metals in unregulated domestic wells in Nevada, USA

The dominant source of drinking water in rural Nevada, United States, is privately-owned domestic wells. Because the water from these wells is unregulated with respect to government guidelines, it is the owner's responsibility to test their groundwater for heavy metals and other contaminants. Arsenic, lead, cadmium, and uranium have been previously measured at concentrations above Environmental Protection Agency (EPA) guidelines in Nevada groundwater. This is a public health concern because elevated levels of these metals are known to have negative health effects. We recruited individuals through a population health study, the Healthy Nevada Project, to submit drinking water samples from domestic wells for testing. Water samples were returned from 174 households with private wells. We found 22 % had arsenic concentrations exceeding the EPA maximum contaminant level (MCL) of 10 μg/L. Additionally, federal, state, or health-based guidelines were exceeded for 8 % of the households for uranium and iron, 6 % for lithium and manganese, 4 % for molybdenum, and 1 % for lead. The maximum observed concentrations of arsenic, uranium, and lead were ∼80, ∼5, and ∼1.5 times the EPA guideline values, respectively. 41 % of households had a treatment system and submitted both pre- and post-treatment water samples from their well. The household treatments were shown to reduce metal concentrations, but concentrations above guideline values were still observed. Many treatment systems cannot reduce the concentration below guideline values because of water chemistry, treatment failure, or improper treatment techniques. These results show the pressing need for continued education and outreach on regular testing of domestic well waters, proper treatment types, and health effects of metal contamination. These findings are potentially applicable to other arid areas where groundwater contamination of naturally occurring heavy metals occurs.

M. Arienzo, D. Saftner, S. N. Bacon, E. Robtoy, I. Neveux, K. Schlauch, M. Carbone, and J. Grzymski,Naturally occurring metals in unregulated domestic wells in Nevada, USA, Sci Total Environ, 2022, 851, 158277.

A review of research on the molybdenum requirements of New Zealand pastures

The requirement for molybdenum (Mo) for legume and pasture growth on New Zealand soils was first identified in the 1950s and most of the research was carried out up to the 1980s. This resulted in a recommendation to apply 56-70 g/ha of sodium molybdate every 4-5 years that was later modified to 50 g/ha every five years. On most soils, the availability of Mo increased with soil pH but the rates of lime required were uneconomic on hill country pastures so Mo was applied as the most cost-effective option. Measuring available soil Mo was a poor predictor of pasture yield responses to Mo compared with the Mo content of clover. More recent research showed that the Mo content of clover had to be less than 0.1 ppm and nitrogen (N) content less than about 4.5% for a definite response in yield to applied Mo to occur. High natural levels of soil Mo elevating pasture Mo content above 0.5-1 ppm or overuse of fertiliser Mo where pasture copper (Cu) is low (<5 ppm for sheep, <10 ppm for cattle and deer) can cause less Cu to be adsorbed from the rumen and reduce animal growth.

D. Morton,A review of research on the molybdenum requirements of New Zealand pastures, New Zealand Journal of Agricultural Research.

ENVIRONMENTAL

MOLYBDATE− Molybdenum accumulation in sediments: a quantitative indicator of hypoxic water conditions in Narragansett Bay, RI

Authigenic molybdenum Mo  accumulation in marine sediments has often been used as a qualitative indicator of hypoxic bottom water. To investigate its use as a quantitative indicator of hypoxic exposure, sediment cores were collected from water quality monitoring sites in Narragansett Bay RI, USA  that experience varying periods of hypoxia. Total Mo concentrations in surficial 0-1 cm  sediments were determined by total digestion and ICP-MS analysis. Lithogenic contributions to total Mo concentrations were estimated by multiplying measured concentrations of aluminum Al  by the mean crustal Mo:Al ratio and subtracting them from the total concentrations to yield the authigenic fraction. 210 Pb dating was used to determine sediment accumulation rates at each site. Mean annual periods of hypoxia in bottom waters were determined from continuous monitoring data for the years coinciding with the top 1 cm of sediment. Results indicated a linear relationship between authigenic Mo concentrations and frequency of hypoxia, although the relationships differed between different sampling periods. These results demonstrate the potential of sedimentary Mo as a tool for assessing the spatial and temporal extent of hypoxia in coastal waters.

W. S. Boothman, L. Coiro, and S. B. Moran,Molybdenum accumulation in sediments: a quantitative indicator of hypoxic water conditions in Narragansett Bay, RI, Estuar Coast Shelf Sci, 2022, 267, 1-10.

MOLYBDATE− Improving monitoring of fish health in the oil sands region using regularization techniques and water quality variables

Trout-perch are sampled from the Athabasca River in Alberta, Canada, as a sentinel species for environmental health. The performance of trout-perch populations is known to be influenced by the quality of the water in which they reside. Using climate, environmental, and water quality variables measured in the Athabasca River near trout-perch sampling locations is found to improve model fitting and the predictability of models for the adjusted body weight, adjusted gonad weight, and adjusted liver weight of trout-perch. Given a large number of covariables, three variable selection techniques: stepwise regression, the lasso, and the elastic net EN  are considered for selecting a subset of relevant variables. The models selected by the lasso and EN are found to outperform the models selected by stepwise regression in general, and little difference is observed between the models selected by the lasso and EN. Uranium, tungsten, tellurium, pH, molybdenum, and antimony are selected for at least one fish response.

P. G. McMillan, Z. Z. Feng, L. E. Deeth, and T. J. Arciszewski,Improving monitoring of fish health in the oil sands region using regularization techniques and water quality variables, Sci Total Environ, 2022, 811, 152301.

MOLYBDATE− Ecotoxicological risk ranking of 19 metals in the lower Yangtze River of China based on their threats to aquatic wildlife

With thousands of chemicals discharged into the aquatic environment, it is necessary to identify those that are likely to be having the greatest impact on wildlife to better protect the ecosystem. A risk ranking approach was developed to compare the ecotoxicological risk of chemicals on aquatic wildlife with a wide range of environmental measurement data and ecotoxicity data. Nineteen metals including some rarely monitored ones including antimony Sb , molybdenum Mo , cobalt Co , vanadium V , titanium Ti  and thallium Tl  in the lower Yangtze River were risk ranked as a case study. The risk ranking approach was conducted in three tiers: general risk ranking, lethal effects vs. non-lethal effects risk ranking, and species group-specific risk ranking. Iron, copper and titanium were identified as being of greatest concern. The contamination of iron, zinc, copper and nickel was widespread and may have already harmed wildlife according to the overlap between ecotoxicity and monitored levels. Based on this analysis, the risk from copper and some rarely monitored metals titanium and boron  may have been underestimated. Greater efforts to reduce copper, iron and titanium contamination could make an important difference to the health of Chinese freshwater organisms in the Yangtze River.

Y. Zhang, M. Zhang, W. Yu, J. Li, and D. Kong,Ecotoxicological risk ranking of 19 metals in the lower Yangtze River of China based on their threats to aquatic wildlife, Sci Total Environ, 2022, 812, 152370.

MoS₂⁻ Environmental implications of MoS₂ nanosheets on rice and associated soil microbial communities

Molybdenum disulfide MoS₂  is a transition metal dichalcogenides TMDCs  material that is seeing rapidly increasing use. The wide range of applications will result in significant environmental release. Here, the impact of MoS₂ nanosheets on rice and associated soil microbial communities was evaluated. Rice plants were grown for 4 weeks in a natural paddy soil amended with either 1T or 2H phase MoS₂ nanosheets at 10 and 100 mg kg^-1 . The 1T MoS₂ nanosheets have a significantly greater dissolution rate 58.9%  compared to 2H MoS₂ 4.4% , indicating the instability of 1T MoS₂ in environment. High dissolution rate resulted in a high Mo bioaccumulation in rice leaves 272 and 189 mg kg^-1  under 1T and 2H exposure at 100 mg kg^-1  . However, this did not induce overt phytotoxicity, as indicated by a range of phenotypic or biochemical based determine endpoints, e.g_., biomass, photosynthetic pigments, and malondialdehyde MDA  content. Additionally, rice P uptake was significantly increased upon exposure to 1T and 2H MoS₂ 10 mg kg^-1  . Gas chromatography-mass spectrometry GC-MS  reveals that both phases of MoS₂ in soil systematically enhanced the carbon and nitrogen related metabolic pathways in exposed plants. Soil 16S rRNA gene sequencing data show that soil microbial community structure was unchanged upon MoS₂ exposure. However, both phases of MoS₂ remarkably increased the relative abundance of N₂-fixation cyanobacteria, and 2H MoS₂ exposure increased a plant growth-promoting rhizobacteria-Bacillus. Overall, our results suggest that MoS₂ nanosheets at tested doses did not exert negative impacts on rice plant and the associated soil microbial community.

L. Zhao, S. Chen, X. Tan, X. Yan, W. Zhang, Y. Huang, R. Ji, and J. C. White,Environmental implications of MoS₂ nanosheets on rice and associated soil microbial communities, Chemosphere, 2022, 291, 133004.

ENVIRONMENT

06 Evaluation of Heavy Metals in Soil Wastewater Stream

Environmental pollution is one of the main factors that significantly affect biological systems and human health. Soil pollution with heavy metals is an increasingly pressing problem worldwide. In general, heavy metals are stable and do not decompose, unlike other organic pollutants. The quantity of them is natural components of soil crust, the remaining come from human activities, which may result from the extensive use of sewage. In the present study, a methodology aimed at simultaneous quantification of 16 heavy elements in soil of 3 different regions was developed. The concentration of 16 soil heavy metals (Se, Cd, V, Be, As, Mn, Co, Zn, Fe, Cr, Pb, Ni, Cu, Mo, Hg, and Ti) was measured in 11 sampling along Riyadh, Qassim, and Medina, Kingdom of Saudi Arabia from 3 sites soil treated with sewage water. These chemical minerals were identified in the samples using an ICPE-9000 spectrometer. The assessment of heavy metal contamination was derived using enrichment factors (EF), the pollution load index (PLI), and geoaccumulation index (I-geo). This study revealed that the soil is predominantly polluted by Cd, As, and Mo of Riyadh and Medina and As, Mo, and Cd of Qassim region at site B and site C, respectively. As recorded, the highest concentration value of 5000 mg/kg for Fe at site (B) followed by Cu. The I-geo value of Cd is 1.1520 in Medina region. The I-geo value of Se is 3.2395 in Medina region, while its cumulative geographical index decreased in the regions of Riyadh and Qassim, which amounted to 2.6114 and 2.1699, respectively. The I-geo values of the rest of the minerals in the three regions studied indicated that the soil is unpolluted, while it was slightly to moderately polluted for both Mo and Hg in most regions studied. The minerals in the soil at all sites studied were less than the general average concentration. With the exception of mercury, molybdenum, arsenic, cadmium, and selenium, whose concentration exceeded the permissible and recommended limits. The increasing order of concentration of minerals was Be < V < Cd < Hg < Mo < Co < Zn < Pb < Cr < Se < As < Ni < Ti < Mn < Cu < Fe at all sites, respectively.

1. A. Alnuwaiser,Evaluation of Heavy Metals in Soil Wastewater Stream, International Journal of Analytical Chemistry, 2022, 2022.

06 Naturally occurring metals in unregulated domestic wells in Nevada, USA

The dominant source of drinking water in rural Nevada, United States, is privately-owned domestic wells. Because the water from these wells is unregulated with respect to government guidelines, it is the owner's responsibility to test their groundwater for heavy metals and other contaminants. Arsenic, lead, cadmium, and uranium have been previously measured at concentrations above Environmental Protection Agency (EPA) guidelines in Nevada groundwater. This is a public health concern because elevated levels of these metals are known to have negative health effects. We recruited individuals through a population health study, the Healthy Nevada Project, to submit drinking water samples from domestic wells for testing. Water samples were returned from 174 households with private wells. We found 22 % had arsenic concentrations exceeding the EPA maximum contaminant level (MCL) of 10 μg/L. Additionally, federal, state, or health-based guidelines were exceeded for 8 % of the households for uranium and iron, 6 % for lithium and manganese, 4 % for molybdenum, and 1 % for lead. The maximum observed concentrations of arsenic, uranium, and lead were ∼80, ∼5, and ∼1.5 times the EPA guideline values, respectively. 41 % of households had a treatment system and submitted both pre- and post-treatment water samples from their well. The household treatments were shown to reduce metal concentrations, but concentrations above guideline values were still observed. Many treatment systems cannot reduce the concentration below guideline values because of water chemistry, treatment failure, or improper treatment techniques. These results show the pressing need for continued education and outreach on regular testing of domestic well waters, proper treatment types, and health effects of metal contamination. These findings are potentially applicable to other arid areas where groundwater contamination of naturally occurring heavy metals occurs.

1. M. Arienzo, D. Saftner, S. N. Bacon, E. Robtoy, I. Neveux, K. Schlauch, M. Carbone, and J. Grzymski,Naturally occurring metals in unregulated domestic wells in Nevada, USA, Sci Total Environ, 2022, 851, 158277.

06 A review of research on the molybdenum requirements of New Zealand pastures

The requirement for molybdenum (Mo) for legume and pasture growth on New Zealand soils was first identified in the 1950s and most of the research was carried out up to the 1980s. This resulted in a recommendation to apply 56-70 g/ha of sodium molybdate every 4-5 years that was later modified to 50 g/ha every five years. On most soils, the availability of Mo increased with soil pH but the rates of lime required were uneconomic on hill country pastures so Mo was applied as the most cost-effective option. Measuring available soil Mo was a poor predictor of pasture yield responses to Mo compared with the Mo content of clover. More recent research showed that the Mo content of clover had to be less than 0.1 ppm and nitrogen (N) content less than about 4.5% for a definite response in yield to applied Mo to occur. High natural levels of soil Mo elevating pasture Mo content above 0.5-1 ppm or overuse of fertiliser Mo where pasture copper (Cu) is low (<5 ppm for sheep, <10 ppm for cattle and deer) can cause less Cu to be adsorbed from the rumen and reduce animal growth.

1. D. Morton,A review of research on the molybdenum requirements of New Zealand pastures, New Zealand Journal of Agricultural Research.

ENVIRONMENTAL

06 Combining metal and sulfate isotopes measurements to identify different anthropogenic impacts on dissolved heavy metals levels in river water

Dissolved heavy metals (DHMs) contamination has raised global concern for ecological and human health development. Weathering of sulfide-bearing ore metals can produce acidic, sulfate-rich solutions in the presence of water and oxygen (O(2)), and DHMs are released to deprave the river water quality. Sulfur and oxygen isotope signatures (δ(34)S(SO4) and δ(18)O(SO4)) could identify this pyrite-derived sulfate; however, it is yet not well known whether the δ(34)S(SO4) and δ(18)O(SO4) values could limit the DHMs sources and illustrate anthropogenic impacts on DHMs along the river corridor. We tried to solve this problem through field works in the Luohe River and Yihe River, two tributaries of the Yellow River, China, where metal sulfide mine activities mostly occurred upstream, but agricultural and domestic behaviors concentrated in the lower plain reaches. In the Luohe River upper areas, δ(34)S(SO4) values had negative correlations with concentrations of cadmium (Cd) (p < 0.01), nickel (Ni) (p < 0.05), molybdenum (Mo) (p < 0.01), uranium (U) (p < 0.01), and SO(4)(2-) (p < 0.01). However, as the δ(34)S(SO4) values increased downstream in the Luohe River, concentrations of copper (Cu) (p < 0.05), mercury (Hg) (p < 0.05), Ni (p < 0.05), and SO(4)(2-) (p < 0.01) simultaneously elevated. The Bayesian Isotope Mixing Model (BIMM) results via δ(34)S(SO4) values demonstrated 64.3%-65.3% of SO(4)(2-) from acid mine drainage (AMD) in the Luohe River's upper reaches and 63.5%-67.7% in the Yihe River's upper reaches, and about 33% from sewage and industrial effluents in the Luohe River's lower reaches and 27% in Yihe River's lower reaches. Our results confirmed the different anthropogenic impacts on the DHMs concentrations in Luohe River and Yihe River and provided a robust method for DHMs sources appointment and pollution management in river systems.

1. Zhang, D. Zhang, H. Z. Duan, Z. Q. Zhao, J. W. Zhang, X. Y. Huang, B. J. Ma, and D. S. Zheng,Combining metal and sulfate isotopes measurements to identify different anthropogenic impacts on dissolved heavy metals levels in river water, Chemosphere, 2023, 310, 136747.

06 Liming alkaline clay soils: effects on soil structure, nutrients, barley growth and yield

Liming before cultivation of sugar beets is favourable even on alkaline soils but knowledge of response in other crops is lacking. Therefore, effects of ground limestone (GL) and structure lime (SL1 slaked lime or SL2 mix of ground limestone and slaked lime) were evaluated in southern Sweden on soil structure, growth and nutrient concentration in barley under four fertilisation strategies 1.5-2 years after application. All lime products increased aggregate stability, but with variations between locations. A lower proportion of large aggregates was found in both limed treatments, and a higher proportion of small aggregates in SL. In barley, grain yield was unaffected while shoot numbers and biomass in first node stage increased for GL and biomass increased further for SL. Structure lime increased potassium concentration in plants in first node stage, due to more potassium in the product. Both lime types increased molybdenum concentration. Ground limestone reduced zinc concentration compared with no liming. Finer seedbed tilth and increased aggregate stability may explain increased biomass for GL. Higher potassium content in SL might be a further explanation. No interactions between liming and fertilisation were found. In conclusion, on the soil types studied, no change of fertilisation strategy is needed due to liming.

1. Gunnarsson, J. Blomquist, L. Persson, A. Olsson, K. Hamner, and K. Berglund,Liming alkaline clay soils: effects on soil structure, nutrients, barley growth and yield, Acta Agriculturae Scandinavica Section B-Soil and Plant Science, 2022, 72, 803-817.

06 Naturally occurring metals in unregulated domestic wells in Nevada, USA

The dominant source of drinking water in rural Nevada, United States, is privately-owned domestic wells. Because the water from these wells is unregulated with respect to government guidelines, it is the owner's responsibility to test their groundwater for heavy metals and other contaminants. Arsenic, lead, cadmium, and uranium have been previously measured at concentrations above Environmental Protection Agency (EPA) guidelines in Nevada groundwater. This is a public health concern because elevated levels of these metals are known to have negative health effects. We recruited individuals through a population health study, the Healthy Nevada Project, to submit drinking water samples from domestic wells for testing. Water samples were returned from 174 households with private wells. We found 22 % had arsenic concentrations exceeding the EPA maximum contaminant level (MCL) of 10 mu g/L. Addition-ally, federal, state, or health-based guidelines were exceeded for 8 % of the households for uranium and iron, 6 % for lithium and manganese, 4 % for molybdenum, and 1 % for lead. The maximum observed concentrations of arsenic, uranium, and lead were-80,-5, and-1.5 times the EPA guideline values, respectively. 41 % of households had a treatment system and submitted both pre-and post-treatment water samples from their well. The household treat-ments were shown to reduce metal concentrations, but concentrations above guideline values were still observed. Many treatment systems cannot reduce the concentration below guideline values because of water chemistry, treatment failure, or improper treatment techniques. These results show the pressing need for continued education and outreach on regular testing of domestic well waters, proper treatment types, and health effects of metal contam-ination. These findings are potentially applicable to other arid areas where groundwater contamination of naturally occurring heavy metals occurs.

1. M. Arienzo, D. Saftner, S. N. Bacon, E. Robtoy, I. Neveux, K. Schlauch, M. Carbone, and J. Grzymski,Naturally occurring metals in unregulated domestic wells in Nevada, USA, Science of the Total Environment, 2022, 851.

06 Trace metals distribution between the surface waters of the Gulf of Cadiz and the Alboran Sea

This study was conducted to address the changes in the surface distribution of trace metals (cobalt, copper, iron, cadmium, nickel, zinc, lead and molybdenum) as they are advected from the Gulf of Cadiz to the Alboran Sea, through the Strait of Gibraltar (south Iberian Peninsula), regions of great ecosystemic importance. Trace metals concentrations were measured in samples collected during two oceanographic cruises, together with the main factors affecting their spatial distribution and temporal variability (i.e., wind and surface currents). Several rivers, the main source of trace metals in this region, flow into the Gulf of Cadiz which is connected with the Alboran Sea through the Strait of Gibraltar by the general circulation pattern. The surface circulation pattern leads to an offshore-eastward gradient that is highly influenced by wind variability. An increase in vertical turbulence induced by the winds or the tidal cycle causes the dilution of trace metals' concentration by mixing rich-metal superficial waters with poor-metal subsurface waters. Additionally, along the eastward displacement of surface waters, several water retention zones have been described (Trafalgar, Camarinal, the Coastal Cyclonic Gyre) that imply an increase in trace metals concentration close to the coast. In addition, our results suggest that the coastal edges of the Strait of Gibraltar also act as a source of certain metals to the Alboran Sea, probably due to the industries in the proximity areas.

1. A. Orihuela-García, M. Bolado-Penagos, I. Sala, A. Tovar-Sánchez, C. M. García, M. Bruno, F. Echevarría, and I. Laiz,Trace metals distribution between the surface waters of the Gulf of Cadiz and the Alboran Sea, Sci Total Environ, 2023, 858, 159662.

06 Two dimensional (2D) materials and biomaterials for water desalination; structure, properties, and recent advances

BACKGROUND: An efficient solution to the global freshwater dilemma is desalination. MXene, Molybdenum Disulfide (MoS₂), Graphene Oxide, Hexagonal Boron Nitride, and Phosphorene are just a few examples of two-dimensional (2D) materials that have shown considerable promise in the development of 2D materials for water desalination. However, other promising materials for desalinating water are biomaterials. The benefits of bio-materials are their wide distribution, lack of toxicity, and superior capacity for water desalination. METHODS: For the rational use of water and the advancement of sustainable development, it is of the utmost importance to research 2D-dimensional materials and biomaterials that are effective for water desalination. The scientific community has concentrated on wastewater remediation using bio-derived materials, such as nanocellulose, chitosan, bio-char, bark, and activated charcoal generated from plant sources, among the various endeavors to enhance access to clean water. Moreover, the 2D-materials and biomaterials may have ushered in a new age in the production of desalination materials and created a promising future. RESULTS: and conclusions The present review article focuses on and reviews the progress of 2D materials and biomaterials for water desalination. Their properties, surface, and structure, combined with water desalination applications, are highlighted. Further, the practicability and potential future directions of 2D materials and biomaterials are proposed. Thus, the current work provides information and discernments for developing novel 2D materials and biomaterials for wastewater desalination. Moreover, it aims to promote the contribution and advancement of materials for water desalination, fabrication, and industrial production.

1. Raza, E. Ghasali, Y. Orooji, H. Lin, C. Karaman, E. N. Dragoi, and N. Erk,Two dimensional (2D) materials and biomaterials for water desalination; structure, properties, and recent advances, Environ Res, 2022, 114998.

06 Water and sediment geochemistry of an urban lake: Implications to weathering and anthropogenic activity

Lakes are sensitive ecosystems and respond quickly to any natural or anthropogenic contamination, particularly in urban areas due to poor planning and mismanagement in urban settlement, encroachment, and anthropogenic pollution. In the current study, water and sediment geochemistry are used along with available time series of geospatial data sets to assess: a) provenance and sources of pollution in the lake sediment and water, b) health risk using various sediment and water quality indices, and c) the key drivers of lake shrinkage. Chemical index of alteration (CIA) of lake sediment is higher (>85) with an atypical cluster of samples (CIA 50-75) towards the south and west of the lake. Further, samples in this cluster show granodioritic provenance which is contrary to the overall mafic provenance of lake sediment. The unusual decrease in CIA in the southern and western side of the lake is attributed to anthropogenically induced fresh sediment in the lake. The results indicate that the sediment is highly polluted by cadmium (Cd) and moderately polluted by copper (Cu), molybdenum (Mo), lead (Pb), and boron (B). Higher Metal Index (MI) values for most of the water samples (>70%) and Hazard Index (HI) for chromium (Cr), nickel (Ni), and cadmium (Cd) towards west and south of the lake reflect the deterioration of water quality in the lake. Moreover, land use change detection attained from available time series of geospatial data sets indicate a drastic transformation of the open water area into other land use classes particularly human settlement, shrinking the lake open water area by 13 km(2) since 1859. The current study will help policy makers and managers to restore and conserve the lake. (C) 2022 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research. Published by Elsevier B.V. All rights reserved.

1. Saleem, G. Jeelani, I. A. Pall, J. Ganai, and S. Kumar,Water and sediment geochemistry of an urban lake: Implications to weathering and anthropogenic activity, International Journal of Sediment Research, 2022, 37, 809-822.

06MoS₂ The role of transformation in the risks of chemically exfoliated molybdenum disulfide nanosheets to the aquatic environment

While the effects of environmental factors (e.g., coexisting organic macromolecules and solar irradiation) on the phase transformation and oxidative dissolution of chemically exfoliated molybdenum nanosheets (ceMoS₂) have been recognized, the effects of environmental processes on the subsequent biological impacts of ceMoS₂ are still poorly understood. In this study, the bioavailability and transitions in chemical speciation occurring during the aging process are demonstrated to be key factors causing ceMoS₂ to affect aquatic organisms. The lower survival rate of embryonic zebrafish with aged (i.e., sunlight-irradiated and dark-ambient-aged) ceMoS₂, compared to that with freshly prepared ceMoS₂, was due to the release of ionic aging products (mainly acidic Mo species) throughout the oxidative dissolution of ceMoS₂. The released soluble molybdenum interacted with natural organic matter (NOM) depending on their functionality, and this attenuated the toxicity caused by ceMoS₂ to different degrees. Toxicity triggered by aged ceMoS₂ under both dark and irradiated conditions was significantly reduced by Suwannee River NOM due to the formation of complexes with ionic Mo species, which was estab-lished by Mo K-edge X-ray absorption spectroscopy. The findings provide useful insights for comprehending the impacts of ceMoS₂ on aquatic organisms and guidance for the prevention measures necessary in the applications of MoS₂ nanosheets.

1. W. Lee, Y. H. Lai, J. L. Chen, and C. Y. Chen,The role of transformation in the risks of chemically exfoliated molybdenum disulfide nanosheets to the aquatic environment, Journal of Environmental Management, 2022, 324.

ENVIRONMENTAL

MOLYBDATE− Molybdenum accumulation in sediments: a quantitative indicator of hypoxic water conditions in Narragansett Bay, RI

Authigenic molybdenum Mo  accumulation in marine sediments has often been used as a qualitative indicator of hypoxic bottom water. To investigate its use as a quantitative indicator of hypoxic exposure, sediment cores were collected from water quality monitoring sites in Narragansett Bay RI, USA  that experience varying periods of hypoxia. Total Mo concentrations in surficial 0-1 cm  sediments were determined by total digestion and ICP-MS analysis. Lithogenic contributions to total Mo concentrations were estimated by multiplying measured concentrations of aluminum Al  by the mean crustal Mo:Al ratio and subtracting them from the total concentrations to yield the authigenic fraction. 210 Pb dating was used to determine sediment accumulation rates at each site. Mean annual periods of hypoxia in bottom waters were determined from continuous monitoring data for the years coinciding with the top 1 cm of sediment. Results indicated a linear relationship between authigenic Mo concentrations and frequency of hypoxia, although the relationships differed between different sampling periods. These results demonstrate the potential of sedimentary Mo as a tool for assessing the spatial and temporal extent of hypoxia in coastal waters.

W. S. Boothman, L. Coiro, and S. B. Moran,Molybdenum accumulation in sediments: a quantitative indicator of hypoxic water conditions in Narragansett Bay, RI, Estuar Coast Shelf Sci, 2022, 267, 1-10.

MOLYBDATE− Improving monitoring of fish health in the oil sands region using regularization techniques and water quality variables

Trout-perch are sampled from the Athabasca River in Alberta, Canada, as a sentinel species for environmental health. The performance of trout-perch populations is known to be influenced by the quality of the water in which they reside. Using climate, environmental, and water quality variables measured in the Athabasca River near trout-perch sampling locations is found to improve model fitting and the predictability of models for the adjusted body weight, adjusted gonad weight, and adjusted liver weight of trout-perch. Given a large number of covariables, three variable selection techniques: stepwise regression, the lasso, and the elastic net EN  are considered for selecting a subset of relevant variables. The models selected by the lasso and EN are found to outperform the models selected by stepwise regression in general, and little difference is observed between the models selected by the lasso and EN. Uranium, tungsten, tellurium, pH, molybdenum, and antimony are selected for at least one fish response.

P. G. McMillan, Z. Z. Feng, L. E. Deeth, and T. J. Arciszewski,Improving monitoring of fish health in the oil sands region using regularization techniques and water quality variables, Sci Total Environ, 2022, 811, 152301.

MOLYBDATE− Ecotoxicological risk ranking of 19 metals in the lower Yangtze River of China based on their threats to aquatic wildlife

With thousands of chemicals discharged into the aquatic environment, it is necessary to identify those that are likely to be having the greatest impact on wildlife to better protect the ecosystem. A risk ranking approach was developed to compare the ecotoxicological risk of chemicals on aquatic wildlife with a wide range of environmental measurement data and ecotoxicity data. Nineteen metals including some rarely monitored ones including antimony Sb , molybdenum Mo , cobalt Co , vanadium V , titanium Ti  and thallium Tl  in the lower Yangtze River were risk ranked as a case study. The risk ranking approach was conducted in three tiers: general risk ranking, lethal effects vs. non-lethal effects risk ranking, and species group-specific risk ranking. Iron, copper and titanium were identified as being of greatest concern. The contamination of iron, zinc, copper and nickel was widespread and may have already harmed wildlife according to the overlap between ecotoxicity and monitored levels. Based on this analysis, the risk from copper and some rarely monitored metals titanium and boron  may have been underestimated. Greater efforts to reduce copper, iron and titanium contamination could make an important difference to the health of Chinese freshwater organisms in the Yangtze River.

Y. Zhang, M. Zhang, W. Yu, J. Li, and D. Kong,Ecotoxicological risk ranking of 19 metals in the lower Yangtze River of China based on their threats to aquatic wildlife, Sci Total Environ, 2022, 812, 152370.

MoS₂⁻ Environmental implications of MoS₂ nanosheets on rice and associated soil microbial communities

Molybdenum disulfide MoS₂  is a transition metal dichalcogenides TMDCs  material that is seeing rapidly increasing use. The wide range of applications will result in significant environmental release. Here, the impact of MoS₂ nanosheets on rice and associated soil microbial communities was evaluated. Rice plants were grown for 4 weeks in a natural paddy soil amended with either 1T or 2H phase MoS₂ nanosheets at 10 and 100 mg kg^-1 . The 1T MoS₂ nanosheets have a significantly greater dissolution rate 58.9%  compared to 2H MoS₂ 4.4% , indicating the instability of 1T MoS₂ in environment. High dissolution rate resulted in a high Mo bioaccumulation in rice leaves 272 and 189 mg kg^-1  under 1T and 2H exposure at 100 mg kg^-1  . However, this did not induce overt phytotoxicity, as indicated by a range of phenotypic or biochemical based determine endpoints, e.g_., biomass, photosynthetic pigments, and malondialdehyde MDA  content. Additionally, rice P uptake was significantly increased upon exposure to 1T and 2H MoS₂ 10 mg kg^-1  . Gas chromatography-mass spectrometry GC-MS  reveals that both phases of MoS₂ in soil systematically enhanced the carbon and nitrogen related metabolic pathways in exposed plants. Soil 16S rRNA gene sequencing data show that soil microbial community structure was unchanged upon MoS₂ exposure. However, both phases of MoS₂ remarkably increased the relative abundance of N₂-fixation cyanobacteria, and 2H MoS₂ exposure increased a plant growth-promoting rhizobacteria-Bacillus. Overall, our results suggest that MoS₂ nanosheets at tested doses did not exert negative impacts on rice plant and the associated soil microbial community.

L. Zhao, S. Chen, X. Tan, X. Yan, W. Zhang, Y. Huang, R. Ji, and J. C. White,Environmental implications of MoS₂ nanosheets on rice and associated soil microbial communities, Chemosphere, 2022, 291, 133004.

ENVIRONMENT UPTAKE SLUDGE MINING

Evaluating the uptake of ten heavy metals by kidney bean (phaseolus vulgaris l.) grown in a soil-sludge mixture using a regression model

Severe human health risks can be caused by consuming vegetables contaminated by heavy metals (HMs); thus, assessing the HM uptake by these plants is important The current work was performed to construct a regression model for predicting the concentration of ten HMs in four tissues of Phaseolus vulgaris (mots, stems, leaves and pods) based on their concentration in a soil-sludge mixture, soil organic matter (OM) and soil pH. For pods, the regression equation with the highest coefficient of determination (R-2 = 0.99) and model efficiency (ME = 1.00) but the lowest mean normalized bias (MNB = 0.01) was that of cobalt. For leaves, the equation with the highest R-2 (0.90) and ME (0.92) but the lowest MNB (0.001) was that of molybdenum. Comparable findings were obtained for molybdenum in the stems and manganese in the roots. All t values that assessed the difference between the actual and predicted values of the ten HMs in the four tissues were nonsignificant. Thus, these models could be used as a risk assessment tool for P. vulgaris cultivated in soil-sludge combinations.

E. M. Eid, K. H. Shaltout, S. A. M. Alamri, N. A. Sewelam, and T. M. Galal,EVALUATING THE UPTAKE OF TEN HEAVY METALS BY KIDNEY BEAN (PHASEOLUS VULGARIS L.) GROWN IN A SOIL-SLUDGE MIXTURE USING A REGRESSION MODEL, Applied Ecology and Environmental Research, 2020, 18, 7021-7039.

Effects of a century of mining and industrial production on metal contamination of a model saline ecosystem, Great Salt Lake, Utah

Effects of mining and metals production have been reported in freshwater lake sediments from around the world but are rarely quantified in saline lake sediments, despite the importance of these lake ecosystems. Here we used dated sediment cores from Great Salt Lake, Utah, USA, a large saline lake adjacent to one of the world's largest copper mines, to measure historical changes in the deposition of 22 metals. Metal concentrations were low prior to the onset of mining in the catchment in 1860 CE. Concentrations of copper, lead, zinc, cadmium, mercury, and other metals began increasing in the late 1800s, with peaks in the 1950s, concomitant with enhanced mining and smelting activities. Sedimentary metal concentrations in the 1950s were 20-40-fold above background levels for copper, lead, silver, and molybdenum. Concentrations of most metals in surficial sediments have decreased 2-5-fold, reflecting: 1) storage and mineralization of sedimenting materials in a deep brine layer, thereby reducing metal transport to the sediments; 2) improved pollution control technologies, and; 3) reduction in mining activity beginning in the 1970s and 1980s. Despite reductions, concentrations of many metals in surficial sediments remain above acceptable contamination thresholds for aquatic ecosystems with migratory birds, and consumption advisories for mercury have been placed on three waterfowl species. The research also highlights that metal deposition in saline lakes is complicated by effects of hypersaline brines and deep-water anoxia in regulating sediment redox and release of metals to surface waters. Given the importance of saline lakes to migratory birds, metals contamination from mining and metals production should be a focus of saline lake remediation. (C) 2020 Elsevier Ltd. All rights reserved.

W. A. Wurtsbaugh, P. R. Leavitt, and K. A. Moser,Effects of a century of mining and industrial production on metal contamination of a model saline ecosystem, Great Salt Lake, Utah, Environmental Pollution, 2020, 266, 115072.

Molybdenum in the Atmosphere

Release of molybdenum into the environment can occur through weathering, agricultural uses of molybdenum compounds, and industrial processes. Molybdenum in air has a range of values. Molybdenum concentrations in air are higher in urban areas than in rural areas. The combustion of fossil fuels is a constant source of molybdenum [Parker, 1986]. Relatively high concentrations are present in air-borne ash expelled usually during the combustion of fossil fuels.

[US DHEW, 1966; Adler, 1957; Adkins and Losee, 1970; Allaway et al., 1968; Anderson, 1966; Anderson and Grensfelt, 1973.]
Parker, G. A., Molybdenum in: Hutzinger, O. (ed.), Handbook of Environmental Chemistry , 1986, 3D, 217. Springer-Verlag, Berlin.
US DHEW, Air Quality Data, National Air Sampling Network, 1966, Public Health Service.
Adler, P., Odont. Révy Suppl., 1957, 48.
Adkins, B. L. and Losee, F. L., N.Y. State dent. J., 1970, 36, 618.
Allaway, W. H., Kubota, J., Losee, F. L. and Roth, M., Arch. Environ. Health, 1968, 16, 342.
Anderson, R. J., Brit. dent. J., 1966, 120, 271.
Anderson, G. and Grensfelt, P., IVL, Gothenburg B, 1973, 138.

ATMOSPHERE

Particulate matter in lung fluid

Workplace exposure to particulate matter, bio-accessible, and non-soluble metal compounds during hot work processes

While exposure to air contaminants from metal arc welding at workplaces has been intensively investigated over the last five decades, other hot work processes, such as flame and plasma cutting, air carbon arc gouging, and surface grinding have not received as much attention. Exposures to particulate matter (PM) during selected hot work processes, such as metal active gas (MAG) and manual metal arc (MMA) welding, flame and plasma cutting, air carbon arc gouging, and surface grinding were measured. Respirable, inhalable, and "total" fractions of the PM were collected with different air samplers in the workers' breathing zone. Concentrations of PM, chromium (Cr), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), and lead (Pb) were determined in the samples by using gravimetric analysis and plasma-based analytical atomic spectrometry techniques. Bio-accessibility of the elements was investigated by using a synthetic lung lining fluid (Hatch s solution) for the leaching of soluble metal compounds in the collected samples. Short term (15-75 min) workplace air concentrations of PM, Cr, Fe, Mn, Ni and Cu in the workers breathing zone during hot work processes were found to be high compared to the current 8-hr time-weighted average (TWA) exposure limit values (ELVs) in use in many countries. The short-term median concentrations of PM during the different hot work processes varied between 6.0 and 88.7 mg m(-3) and between 15.1 and 193 mg m(-3) in the respirable and inhalable fractions, respectively. The highest median concentration of Fe (107 mg m(-3)) and Mn (28.7 mg m(-3)) was found in the inhalable fraction during plasma cutting and air carbon arc gouging, respectively. More than 40% of the inhalable PM generated during flame and plasma cutting, air carbon arc gouging and surface grinding was present in the respirable fraction. There was large variation in the bio-accessibility of the elements in PM collected during the different hot work processes.

B. Berlinger, U. Skogen, C. Meijer, and Y. Thomassen,Workplace exposure to particulate matter, bio-accessible, and non-soluble metal compounds during hot work processes, Journal Of Occupational And Environmental Hygiene 2019, 16, 378–386.

See also B. Berlinger et al., A study of the bio-accessibility of welding fumes, J. Environ. Monit., 2008, 10, 1448–1453.

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[3] Anderson, G., Grensfelt, P., IVL, Gothenburg B, 1973, 138.
(Quoted in J. Lener and B. Bibr, J. Hygiene, Epidemiology, Microbiol. and Immunol., 1984, 28, 405).
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Mo in ambient air urban areas 0.01 – 0.03 microg Mo/m3
Rural areas 0.001 – 0.0032

Schroeder, H.A., A sensible look at air pollution by metals, Arch. Environ. Health, 1970, 21, 798 – 806.

Concentrations of molybdenum and other metals were determined in ambient air as part of an ongoing air-quality monitoring programme.the mass concentrations and metals speciation of ambient aerosols collected in Oxford, OH were compared with those collected in three urban centers (Cincinnati, Middletown, and Hamilton) in the Greater Cincinnati region. PM2.5 particles (< 2.5 microm) typically originates from the combustion of fossil fuels for power and transportation and from manufacturing processes. The mean PM2.5, PM10 and TSP mass concentrations (microg m^-3) of the samples collected in 2005 in Oxfordwere: PM2.5, 15.6±8.1, PM10, 16.2±7.3; TSP, 37.0±7.8. The PM2.5 contributed 95% to PM10 and 60% to TSP (total suspended solids). Arsenic, antimony, cobalt, and lead were predominantly contained in PM2.5; cadmium, chromium, iron, nickel, molybdenum, silicon, vanadium, and zinc in PM10.. Since these metals are typically associated with anthropogenic metals emissions (traffic, combustion of fossil fuels, industry) and it was expected that these metals would be present in the smaller particle size ranges.

Wojas, B. and Almquist, C., Mass concentrations and metals speciation of PM2.5, PM10, and total suspended solids in Oxford, Ohio and comparison with those from metropolitan sites in the Greater Cincinnati region, Atmospheric Environment, 2007, 41, 9064-9078.