Adsorption kinetic characteristics of molybdenum in yellow-brown soil in response to pH and phosphate
Molybdenum (Mo) adsorption by acidic yellow-brown soil was investigated as a function of a pH (1-13) and the equilibrium of phosphate solution (0, 3.1, and 31 mg L-1) concentration. Mo adsorption by acidic yellow-brown soil increased within the pH range from 1 to 4. Above pH 4, Mo adsorption decreases with an increase in pH. The maximum adsorption was found between pH 2 and 4. Competitive adsorption experiments showed that the equilibrium sorption data fitted into Langmuir and Freundlich isotherms. The sorption data of Mo on the acidic yellow-brown soil fitted well with the Langmuir isotherm model due to the higher R2 value. A reduction in Mo adsorption by the acidic yellow-brown soil was noticed at higher addition levels of phosphate (3.1 and 31 mg L-1). Therefore, phosphate increasing the bioavailability of Mo and enhancing Mo uptake by plants might be related to the inhibition of Mo absorption by the acidic yellow-brown soil.
Z. J. Nie, J. F. Li, H. Y. Liu, S. L. Liu, D. C. Wang, P. Zhao, and H. G. Liu,Adsorption kinetic characteristics of molybdenum in yellow-brown soil in response to pH and phosphate, Open Chemistry, 2020, 18, 663-668.
Kinetic modeling of molybdenum sorption and transport in soils
In this investigation, batch and column experiments were conducted to investigate the molybdenum (Mo) sorption and transport processes on a neutral-pH soil (Webster loam) and an acidic soil (Mahan sand) in Ca2+ and K+ background solutions. Batch results showed that the adsorption of Mo was strongly non-linear in both soils and amount of Mo sorbed in the acidic soil was larger than the neutral soil. The Freundlich distribution coefficients (K(f)) and Langmuir sorption maxima (S(max)) in Ca2+ background solution are larger than that in K+ solution, indicating greater Mo sorption in Ca2+ than in K+. Experimental breakthrough curves (BTCs) demonstrated that mobility of Mo was higher at neutral condition than that at acidic condition. A multi-reaction transport model (MRTM) formulation with two kinetic retention reactions (reversible and irreversible) well described Mo transport for Webster soil. However, MRTM model which accounts for equilibrium and kinetic sites is recommended for Mo transport in Mahan soil, reflecting different soil properties. Based on inverse modeling, the sorption forward rate coefficients (k(1)) obtained from Ca2+ in both soils are larger than that from K+, which consistent with batch experiment. Overall, MRTM model was capable of describing the Mo transport behavior under different geochemical conditions.
W. Sun, and H. M. Selim,Kinetic modeling of molybdenum sorption and transport in soils, Environmental science and pollution research international, 2020, 27, 20227-20234.
What constitutes plant-available molybdenum in sandy acidic soils?
Molybdenum (Mo) is critical for the function of enzymes related to nitrogen cycling. Concentrations of Mo are very low in sandy, acidic soils, and biologically available Mo is only a small fraction of the total pool. While several methods have been proposed to measure plant-available Mo, there has not been a recent comprehensive analytical study that compares soil extraction methods as predictors of plant Mo uptake. A suite of five assays [total acid microwave digestion, ethylenediamenetetraaacetic acid (EDTA) extraction, Environmental Protection Agency (EPA) protocol 3050B, ammonium oxalate extraction, and pressurized hot water] was employed, followed by the determination of soil Mo concentrations via inductively coupled mass spectroscopy. The concentrations of soil Mo determined from these assays and their relationships as predictors of plant Mo concentration were compared. The assays yielded different concentrations of Mo: total digest > EPA > ammonium oxalate ≥ EDTA > pressurized hot water. Legume foliar Mo concentrations were most strongly correlated with ammonium oxalate–extractable Mo from soils, but an oak species showed no relationship with any soil Mo fraction and foliar Mo. Bulk fine roots in the 10- to 30-cm soil horizon were significantly correlated with the ammonium oxalate Mo fraction. There were significant correlations between ammonium oxalate Mo and the oxides of iron (Fe), manganese (Mn), and aluminum (Al). Results suggest that the ammonium oxalate extraction for soil Mo is the best predictor of plant-available Mo for species with high Mo requirements such as legumes and that plant-available Mo tracks strongly with other metal oxides in sandy, acidic soils.
B. D. Duval, S. M. Natali, and B. A. Hungate, What constitutes plant-available molybdenum in sandy acidic soils?, Communications in Soil Science and Plant Analysis, 2015, 46, 318-326
Uptake Prediction of Ten Heavy Metals by Eruca sativa Mill. Cultivated in Soils Amended with Sewage Sludge
This study was carried out to develop mathematical regression equations for predicting the uptake of ten heavy metals (HMs) (cadmium, Cd; cobalt, Co; chromium, Cr; copper, Cu; iron, Fe; manganese, Mn; molybdenum, Mo; nickel, Ni; lead, Pb; zinc, Zn) by a vegetable species (Eruca sativa Mill.) in the Abha region (Saudi Arabia) based on the concentration of these HMs in soils amended with sewage sludge, organic matter (OM) content and soil pH. The resultant regression equations indicated that the three soil factors were significant predictors for the uptake of the ten HMs in the plant tissues. By applying a t test, we found that there are no significant differences between the actual and predicted values of the ten HMs in the E. sativa roots and leaves (P > 0.05), which reflects the goodness of fit of these equations for predicting the uptake of these HMs. Such types of equations may be helpful for evaluating the risk of cultivation of E. sativa plants in soils amended with sewage sludge.
E. M. Eid, K. H. Shaltout, S. M. Abdallah, T. M. Galal, A. F. El-Bebany, and N. A. Sewelam,Uptake Prediction of Ten Heavy Metals by Eruca sativa Mill. Cultivated in Soils Amended with Sewage Sludge, Bulletin of environmental contamination and toxicology, 2019. https://doi.org/10.1007/s00128-019-02746-3.
Molybdenum in the Geosphere
Soil metal/metalloid concentrations in the Clyde Basin, Scotland, UK: implications for land quality
An assessment of topsoil (5-20cm) metal/metalloid (hereafter referred to as metal) concentrations across Glasgow and the Clyde Basin reveals that copper, molybdenum , nickel, lead, antimony and zinc show the greatest 142 Pollution Assessment of Heavy Metals in Soils and Plants around a molybdenum Mine in Central China
Although environmental problems caused by metal mining have become increasingly prominent, the pollution by associated heavy metals is easily neglected. In general, molybdenum mines are low-grade and hence the high level of associated heavy metals easily causes pollution in the surrounding areas. Here we investigated the total concentrations and forms of Mo and associated Cu, Cd, Pb, and Zn in soils under different land-use types (barren, wheat, rape, and apple-seedling fields) and different plants (cultivated crops and wild wormwood) around an abandoned molybdenum tailings site. The results showed that the average total concentrations of Cu and Zn in farmland bulk soils around the site exceeded the level II standard of the National Environmental Quality Standard for Soils in China, the average Cd and Pb concentrations exceeded the level III standard, and the average Mo concentration exceeds the soil background value in Shaanxi Province. The percentages of available heavy metals in wormwood and seedling rhizosphere soils were significantly higher than those in crop rhizosphere soils. Heavy metals mainly accumulated in the roots of plants tested in this study. The Cu, Cd, and Pb concentrations in wormwood exceeded the limits of these metals in general plants. The Cd and Pb pollution indices of corn at the side of the barren land were 3.12 and 2.48, respectively, and the Pb pollution index of rape was 3.42, according to the standard limit of pollutants in food for China. On the basis of the level III standard, the pollution assessment of soils revealed serious pollution of the barren land and wheat fields, and moderate pollution of the rape and seedling fields. This study indicates that the heavy metals associated with the molybdenum mine have polluted the surrounding soils and plants, of which pollution of the barren land is the most serious.
Z. X. Han, D. J. Wan, H. X. Tian, W. X. He, Z. Q. Wang, and Q. Liu,Pollution Assessment of Heavy Metals in Soils and Plants around a molybdenum Mine in Central China, Polish Journal of Environmental Studies, 2019, 28, 123-133.
enrichment in urban versus rural topsoil (elevated 1.7-2.1 times; based on median values). This is a typical indicator suite of urban pollution also found in other cities. Similarly, arsenic, cadmium and lead are elevated 3.2-4.3 times the rural background concentrations in topsoil from the former Leadhills mining area. Moorlands show typical organic-soil geochemical signatures, with significantly lower (P<0.05) concentrations of geogenic elements such as chromium, copper, nickel, molybdenum and zinc, but higher levels of cadmium, lead and selenium than most other land uses due to atmospheric deposition/trapping of these substances in peat. In farmland, 14% of nickel and 7% of zinc in topsoil samples exceed agricultural maximum admissible concentrations, and may be sensitive to sewage-sludge application. Conversely, 5% of copper, 17% of selenium and 96% of pH in farmland topsoil samples are below recommended agricultural production thresholds. Significant proportions of topsoil samples exceed the most precautionary (residential/allotment) human-exposure soil guidelines for chromium (18% urban; 10% rural), lead (76% urban; 45% rural) and vanadium (87% urban; 56% rural). For chromium, this reflects volcanic bedrock and the history of chromite ore processing in the region. However, very few soil types are likely to exceed new chromiumVI-based guidelines. The number of topsoil samples exceeding the guidelines for lead and vanadium highlight the need for further investigations and evidence to improve human soil-exposure risk assessments to better inform land contamination policy and regeneration.
F. M. Fordyce, P. A. Everett, J. M. Bearcock, and T. R. Lister,Soil metal/metalloid concentrations in the Clyde Basin, Scotland, UK: implications for land quality, Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 2019, 108, 191-216.
Impacts of molybdenum-, nickel-, and lithium- oxide nanomaterials on soil activity and microbial community structure
The nano forms of the metals molybdenum oxide (MoO3), nickel oxide (NiO) and lithium oxide (Li2O) are finding wide application in advanced technologies including batteries and fuel cells. We evaluated soil responses to nanoMoO3, nanoNiO, and nanoLi2O as some environmental release of the materials, either directly or following the land application of biosolids, is expected. Using Drummer soil (Fine-silty, mixed, superactive, mesic Typic Endoaquolls), we evaluated the impacts of the three nanometals on soil gas (N2O, CH4, and CO2) emissions, enzyme activities (beta-glucosidase and urease), and microbial community structure (bacterial, archaeal, and eukaryal) in a 60day microcosms incubation. Soil treated with nanoLi2O at 474mugLi/g soil, released 3.45 times more CO2 with respect to the control. Additionally, beta-glucosidase activity was decreased while urease activity increased following nanoLi2O treatment. While no clear patterns were observed for gas emissions in soils exposed to nanoMoO3 and nanoNiO, we observed a temporary suppression of beta-glucosidase activity in soil treated with either metal. All three domains of microbial community were affected by increasing metal concentrations. This is the first evaluation of soil responses to nanoMoO3, nanoNiO, or nanoLi2O.
H. Avila-Arias, L. F. Nies, M. B. Gray, and R. F. Turco,Impacts of molybdenum-, nickel-, and lithium- oxide nanomaterials on soil activity and microbial community structure, The Science of the total environment, 2019, 652, 202-211.
Characterization of vegetable nitrogen uptake and soil nitrogen transformation in response to continuous molybdenum application
Molybdenum (Mo), a plant micronutrient, is involved in nitrogen (N) cycling of global ecosystem, but little is known about its effect on soil N transformation especially the key processes nitrification and denitrification. A long-term field experiment was carried out to investigate the effects of continuous sufficient soil available Mo on vegetable N uptake and soil N transformation. The experiment consisted of three treatments: control (CK), Mo deficiency (NPK), and Mo application (NPK+Mo). The results show that (1) after a 7-year-experiment, continuous Mo application significantly increased soil available Mo content. (2) Compared to the NPK treatment, NPK+Mo treatment showed an increase of 11, 18, and 8% in the cumulative crop yield, plant N uptake, and N fertilizer use efficiency. (3) With continuous Mo application, the soil NO3--N, NH4+-N, microbial biomass N, and total N contents were reduced by 14, 29, 40, and 12%, the soil nitrate reductase (NR) and nitrite reductase (NiR) activities were reduced by 14 and 8%, as well as the potential denitrification activity (PDA) and gross nitrification rate (GNR) were decreased by 64 and 80%, respectively. Additionally, continuous Mo application decreased the abundance of ammonia-oxidizing archaea (AOA) and increased the abundance of narG-containing denitrifiers (narG) and nirK-type nitrite reducers (nirK) significantly. The data suggest that a deficiency in soil available Mo may induce the risk of soil N accumulation and environmental N emission in vegetable soil, whereas continuous Mo application could mitigate this risk by increasing crop yield and N uptake and, by decreasing soil N residues, soil nitrification and denitrification.
X. Wen, C. X. Hu, X. C. Sun, X. H. Zhao, Q. L. Tan, P. J. Liu, J. Xin, S. Y. Qin, and P. C. Wang, Characterization of vegetable nitrogen uptake and soil nitrogen transformation in response to continuous molybdenum application, Journal of Plant Nutrition and Soil Science, 2018, 181, 516-527
Distribution and chemical speciation of molybdenum in river and pond sediments affected by mining activity in Erdenet City, Mongolia
Rivers and ponds near the Erdenet mine, one of the world's largest copper-molybdenum mines, exhibit high concentrations of molybdenum (Mo). This study evaluates the distribution and chemical speciation of Mo in surface sediments from ponds and rivers in Erdenet city to elucidate the mobility and solubility of Mo in the surface aquatic environments in the area. The waters and sediments were collected in two shallow ponds connected to the tailing pond and from three rivers flowing through Erdenet city. The distribution and chemical speciation of Mo in the sediments were examined using five-step sequential extraction and X-ray absorption fine structure (XAFS) analyses. The XAFS spectra of the sediments showed that large amounts of Mo in the sediments are molybdate or polymeric molybdate, weakly adsorbed onto ferrihydrite. Sequential extraction consistently showed a large amount of Mo distributed in the labile fractions. Results suggest that the surface sediments from ponds and rivers play a role as secondary contamination sources of Mo rather than as sinks of Mo in the area.
T. Solongo, K. Fukushi, O. Altansukh, Y. Takahashi, A. Akehi, G. Baasansuren, Y. Ariuntungalag, O. Enkhjin, B. Davaajargal, D. Davaadorj, and N. Hasebe, Distribution and chemical speciation of molybdenum in river and pond sediments affected by mining activity in erdenet city, mongolia, Minerals, 2018, 8.
Spatial distribution and sources of heavy metals in natural pasture soil around copper-molybdenum mine in Northeast China
The characterization of the content and source of heavy metals are essential to assess the potential threat of metals to human health. The present study collected 140 topsoil samples around a Cu-Mo mine (Wunugetushan, China) and investigated the concentrations and spatial distribution pattern of Cr, Ni, Zn, Cu, Mo and Cd in soil using multivariate and geostatistical analytical methods. Results indicated that the average concentrations of six heavy metals, especially Cu and Mo, were obviously higher than the local background values. Correlation analysis and principal component analysis divided these metals into three groups, including Cr and Ni, Cu and Mo, Zn and Cd. Meanwhile, the spatial distribution maps of heavy metals indicated that Cr and Ni in soil were no notable anthropogenic inputs and mainly controlled by natural factors because their spatial maps exhibited non-point source contamination. The concentrations of Cu and Mo gradually decreased with distance away from the mine area, suggesting that human mining activities may be crucial in the spreading of contaminants. Soil contamination of Zn were associated with livestock manure produced from grazing. In addition, the environmental risk of heavy metal pollution was assessed by geo-accumulation index. All the results revealed that the spatial distribution of heavy metals in soil were in agreement with the local human activities. Investigating and identifying the origin of heavy metals in pasture soil will lay the foundation for taking effective measures to preserve soil from the long-term accumulation of heavy metals.
Z. Wang, C. Hong, Y. Xing, K. Wang, Y. Li, L. Feng, and S. Ma,Spatial distribution and sources of heavy metals in natural pasture soil around copper-molybdenum mine in Northeast China, Ecotoxicol Environ Saf, 2018, 154, 329-336.
Selenium Distribution for Soils Derived from Mancos Shale in Gunnison and Uncompahgre River Basins, West-Central Colorado
Selenium (Se) is an essential micronutrient for humans and animals and can be toxic when present in high concentrations in soil and water. Many soils in Gunnison and Uncompahgre River Basins in West-Central Colorado are formed from deposits derived mainly from weathered Mancos shale that have high concentration of Se and salts. Elevated concentrations of Se and salts were detected in streams and rivers in this area. The objectives were to determine the amount and distribution of different forms of Se and relationships with physical and chemical properties for soils derived from Se-rich Mancos shale. The information may help to improve land management practices and minimize the environmental impact on natural water resources. A total of 48 topsoil samples and soils from horizons in 9 pedons were investigated. The total and water-soluble Se and other elements as well as physical and chemical properties were determined in soils. The total Se ranged from 330 to 5,673 mu g/kg with a mean of 2,224 mu g/kg. The water-soluble Se ranged from a minimum of 4.95 mu g/kg to a maximum of 2,415 mu g/kg and a mean of 338 mu g/kg. A highly significant correlation was detected between the total and water-soluble Se in soils. Both the total organic carbon (TOC) and CaCO3% had significant positive correlations with the total Se. A highly significant correlation was also found between the water-soluble Se and electric conductivity (EC), as well as with the water-soluble chloride, sulfate, nitrate, molybdenum, and sodium in soils. For the pedons tested, in general, both the total and water-soluble Se increased with depth. However, the water-soluble Se concentrations were greater in shallow than deep pedons where most Se was removed from soils with drainage water. It could be concluded that Se leaching from topsoils and that dissolving from Se-rich parent materials would be a major source of elevated Se concentrations in streams/rivers for the West-Central Colorado area. To minimize the impact on water quality, an appropriate land/water management practices should be followed to minimize Se leaching from soils derived from Mancos shale.
M. A. Elrashidi,Selenium Distribution for Soils Derived from Mancos Shale in Gunnison and Uncompahgre River Basins, West-Central Colorado, Communications in Soil Science and Plant Analysis, 2018, 49, 1083-1091.
Kinetics of Molybdenum Adsorption and Desorption in Soils
Much uncertainty exists in mechanisms and kinetics controlling the adsorption and desorption of molybdenum(Mo) in the soil environment. To investigate the characteristics of Mo adsorption and desorption and predict Mo behavior in the vadose zone, kinetic batch experiments were performed using three soils: Webster loam, Windsor sand and Mahan sand. Adsorption isotherms for Mo were strongly nonlinear for all three soils. Strong kinetic adsorption of Mo by all soils was also observed, where the rate of retention was rapid initially and was followed by slow retention behavior with time. The time-dependent Mo sorption rate was not influenced when constant pH was maintained. Desorption or release results indicated that there were significant fractions of Mo that appeared to be irreversible or slowly reversibly sorbed by Windsor and Mahan. X-ray absorption near edge structure (XANES) analysis for Windsor and Mahan soils indicated that most of Mo had been bound to kaolinite, whereas Webster had similar XANES features to those of Mo sorbed to montmorillonite. A sequential extraction procedure provided evidence that a significant amount of Mo was irreversibly sorbed. A multireaction model (MRM) with nonlinear equilibrium and kinetic sorption parameters was used to describe the adsorption-desorption kinetics of Mo on soils. Our results demonstrated that a formulation of MRM with two sorption sites (equilibrium and reversible) successfully described Mo adsorption-desorption data for Webster loam, and an additional irreversible reaction phase was recommended to describe Mo desorption or release with time for Windsor and Mahan soils.
W. Sun, and H. M. Selim,Kinetics of Molybdenum Adsorption and Desorption in Soils, Journal of environmental quality, 2018, 47, 504-512
[“The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin for "shallow").
“The phreatic zone, or zone of saturation, is the area in an aquifer, below the water table, in which relatively all pores and fractures are saturated with water. The phreatic zone defines the lower edge of the vadosezone.” Wikipedia]
Plant growth in amended molybdenum mine waste rock
This greenhouse study examined the use of organic and inorganic soil amendments in waste rock material from the former Questa Molybdenum Mine in northern New Mexico to promote beneficial soil properties. Waste rock material was amended with 11 soil amendment treatments that included municipal composted biosolids, BiosolA (R), inorganic fertilizer, and two controls (pure waste rock and sand). Elymus trachycaulus and Robinia neomexicana growth performance and plant chemistry were assessed across all treatments over a period of 99 and 141 days, respectively. Even though waste rock material had more than 200 times the molybdenum concentration of native soils, adverse effects were not observed for either species. The two main limiting factors in this study were soil nutritional status and soil water retention. The biosolid amendment was found to provide the greatest buffer against these limiting factors due to significant increases in both nutrition and soil water retention. As a result, both species responded with the highest levels of biomass production and the least amount of required water demands. Use of organic amendments such as biosolids, even though short lived in the soil, may provide plants the necessary growth stimulus to become more resilient to the harsh conditions found on many mine reclamation sites.
Burney, O. T., Redente, E. F., and Lambert, C. E.,Plant growth in amended molybdenum mine waste rock, Environmental Science and Pollution Research, 2017, 24, 11215-11227.
Soil chemistry and nutrient concentrations in perennial ryegrass as influenced by gypsum and carbon amendments
Plant growth is affected by soil properties that can be improved through addition of amendments and other management practices. Use of gypsum as a soil amendment for improving agricultural yields, and soil and water quality is increasing, but knowledge is lacking on how it affects the soil's chemical properties and plant growth. This greenhouse study measured changes in soil chemistry, growth and nutrient uptake response of ryegrass (Lolium perenne) grown in two contrasting soil types amended with crop residues, glucose, and gypsum. The soil chemical properties, biomass yield, and elemental composition of ryegrass shoots and roots were evaluated. Residue addition significantly increased total soil N and pH, and glucose significantly lowered soil pH. Gypsum significantly increased pH in the 25-40 cm layer only and exchangeable Ca in all layers, and decreased Bray P-1 in the surface layer by 40%. No significant effects were observed in above-ground ryegrass biomass with addition of inputs. Compared to the untreated soil, gypsum increased Ca and S uptake by 50 and 259%, respectively, in the last harvest and Ca, S and Mo in roots by 77, 175, and 18%. Addition of residues and gypsum improved soil chemical properties, nutrient availability, and uptake, but not ryegrass yield.
Walia, M. K., and Dick, W. A.,Soil chemistry and nutrient concentrations in perennial ryegrass as influenced by gypsum and carbon amendments, Journal of Soil Science and Plant Nutrition, 2016, 16, 832-847.