Se Remediation Research Articles

Zero-valent iron (ZVI) facilitated in-situ selenium (Se) immobilization and its recovery by magnetic separation: Mechanisms and implications for microbial ecology

Selenium (Se(VI)) is environmentally toxic. One of the most popular reducing agents for Se(VI) remediation is zero-valent iron (ZVI). However, most ZVI studies were carried out in water matrices, and the recovery of reduced Se has not been investigated. A water-sediment system constructed using natural sediment was employed here to study in-situ Se remediation and recovery. A combined effect of ZVI and unacclimated microorganisms from natural sediment was found in Se(VI) removal in the water phase with a removal efficiency of 92.7 ± 1.1% within 7 d when 10 mg L−1 Se(VI) was present. Soluble Se(VI) was removed from the water and precipitated to the sediment phase (74.8 ± 0.1%), which was enhanced by the addition of ZVI (83.3 ± 0.3%). The recovery proportion of the immobilized Se was 34.2 ± 0.1% and 92.5 ± 0.2% through wet and dry magnetic separation with 1 g L−1 ZVI added, respectively. The 16 s rRNA sequencing revealed the variations in the microbial communities in response to ZVI and Se, which the magnetic separation could potentially mitigate in the long term. This study provides a novel technique to achieve in-situ Se remediation and recovery by combining ZVI reduction and magnetic separation.

Utilizing biochar to decorate nanoscale FeS for the highly effective decontamination of Se(IV) from simulated wastewater

Selenium (Se) as an essential nutrient for human beings at trace concentrations, the allowable concentration for the human is only 40 μg/L. Iron sulfide (FeS) nanoparticles have been applied for excessive of selenium (Se) remediation in surface water and groundwater. In this study, FeS nanoparticles were anchored onto biochar (BC) to reduce agglomeration of FeS and prepared into the composite of FeS-BC by pyrolysis to economically and efficiently remove Se(IV) from simulated wastewater based on the excellent performance of FeS and the low cost of BC. Characterizations presented the uniform anchorage of FeS on the BC surface to prevent agglomeration. The results of batch experiments revealed that the removal of Se(IV) by FeS-BC nanomaterials significantly depended on the pH value, with the maximum removal of ∼174.96 mg/g at pH 3.0. A pseudo-second-order kinetic model well reflected the kinetic removal of Se(IV) in pure Se(IV) solution with different concentration, as well as the coexistence of K+, Ca2+, Cl-, and SO42- ions. The presence of K+ ions significantly inhibited the removal of Se(IV) with the increase of K+ ion concentration compared with the effect of the other three ions. SEM-EDS and XPS analyses indicated that the removal process was achieved through adsorption by surface complexation, and reductive precipitation of Se(IV) into Se0 with the electron donor of Fe(II) and S(-II) ions. The FeS-BC nanomaterial exhibited an excellent application prospect in the remediation of Se(IV).

FeS@h-BN as an adsorbent for the removal of Se (IV) from solution: Characterization and characteristics in a fixed bed column

The removal of selenium (IV) from aqueous solutions was the focus of research that led to the discovery of a novel type of composite adsorbent called FeS@h-BN nanocomposite. This adsorbent was studied, characterized, and put to use in a fixed bed column. SEM, FTIR, XRD, and XPS analyses were conducted to learn more about the coated layer's surface properties. The effect of several adsorbent materials on the remediation of Se(IV) in dynamic water was examined. The Adams-Bohart model, the Thomas model, and the Yoon-Nelson model were all utilized to get optimal fits to the kinetic data obtained from the adsorption process. Moreover, the Adams-Bohart model was only applicable to the beginning portion of the dynamic behavior of the FeS and FeS@h-BN columns. The Thomas and Yoon-Nelson models were sufficient for describing the breakthrough curve under all experimental conditions. For this dynamic process, the theoretical breakthrough curve profile was compared to an experimentally derived profile. It was discovered that FeS@h-BN nanocomposites are the most effective at removing Se(IV), and the adsorption of Se(IV) by a variety of adsorbent materials is enough for all three dynamic models.

A critical analysis of sources, pollution, and remediation of selenium, an emerging contaminant.

Selenium (Se) is an essential metalloid and is categorized as emerging anthropogenic contaminant released to the environment. The rise of Se release into the environment has raised concern about its bioaccumulation, toxicity, and potential to cause serious damages to aquatic and terrestrial ecosystem. Therefore, it is extremely important to monitor Se level in environment on a regular basis. Understanding Se release, anthropogenic sources, and environmental behavior is critical for developing an effective Se containment strategy. The ongoing efforts of Se remediation have mostly emphasized monitoring and remediation as an independent topics of research. However, our paper has integrated both by explaining the attributes of monitoring on effective scale followed by a candid review of widespread technological options available with specific focus on Se removal from environmental media. Another novel approach demonstrated in the article is the presentation of an overwhelming evidence of limitations that various researchers are confronted with to overcome achieving effective remediation. Furthermore, we followed a holistic approach to discuss ways to remediate Se for cleaner environment especially related to introducing weak magnetic field for ZVI reactivity enhancement. We linked this phenomenal process to electrokinetics and presented convincing facts in support of Se remediation, which has led to emerge ‘membrane technology’, as another viable option for remediation. Hence, an interesting, innovative and future oriented review is presented, which will undoubtedly seek attention from global researchers.

Bioremediation of selenium-contaminated soil using earthworm Eisenia fetida: Effects of gut bacteria in feces on the soil microbiome

Selenium (Se) contamination in the soil poses a food safety risk to humans. The present study was to investigate the role of earthworm Eisenia fetida in soil Se remediation. When exposed to selenite at 4 mg Se/kg, E. fetida efficiently concentrated Se in tissues (24.53 mg Se/kg dry weight), however, only accounting for a minor portion of the added Se. Microbial analysis shows 12 out of 15 functional genera became more abundant in the worm-inhabited soil when exposed to Se, suggesting E. fetida contributed to Se remediation mainly by introducing Se-reducing bacteria to the soil via feces, which were dominated by the genera Pseudomonas (∼62.65%) and Aeromonas (∼29.99%), whose abundance was also significantly boosted in the worm-inhabited soil. However, when isolated from worm feces at 200 mg Se/L, Pseudomonas strains only displayed a high tolerance to Se rather than removal capacity. In contrast, among 4 isolated Aeromonas strains, A. caviae rapidly removing 85.74% of the added selenite, mainly through accumulation (67.38%), while A. hydrophila and A. veronii were more effective at volatilizing Se (27.77% and 24.54%, respectively), and A. media performed best by reducing Se by ∼49.00% under anaerobic conditions. Overall, our findings have highlighted the importance of E. fetida as a key contributor of functional bacteria to the soil microbiome, building a strong foundation for the development of an earthworm-soil system for Se bioremediation.

(Invited) Electrochemical Selenium Remediation: Direct Reduction Pathways and System Optimization

Selenium (Se) is a naturally occurring metalloid in the earth's crust that is released through weathering processes. Anthropogenic activities have significantly accelerated geogenic release, increasing Se concentrations in aquatic environments far beyond the ppb levels required for biologic function. Meanwhile, existing biological and physicochemical Se remediation processes are energy-, resource-, and cost-intensive, driving new Se separation processes to consistently meet the WHO and EPA guidelines. Se direct electrochemical reduction (SeDER) is a chemical-free and thermodynamically favorable approach for aquatic Se separation, but evaluating the feasibility of SeDER in application requires a comprehensive understanding of reduction pathways and system-level performance in complex water matrices. This study focuses on the thermodynamic and kinetic performance of SeDER and competing ion behavior in the aquatic environment. Our results indicate that anion structure reorganization hinders process kinetics in electrochemical Se(VI) reduction. However, Se(IV) can be electrochemically separated from the aqueous phase through either a four- or six-electron pathway, with the former generating Se(0) directly attached to the electrode surface and the latter producing Se(-II) that is subsequently converted to Se(0). We demonstrate that raising the solution temperature to 80 C deposits Se(0) in a conductive crystalline form and enables continuous reduction on the electrode surface. We further investigate cathodic and anodic competing ion behavior in both electrochemical pathways. The results suggest that sulfate promotes electrochemical Se(IV) removal efficiency by 11-23%, but nitrate hinders Se(IV) removal (2-11% decrease) by occupying cathodic reaction sites. The anodic competing ions, especially chloride, decrease Se(IV) separation efficiency by generating strong oxidants and disrupting Se(IV) reduction pathways. Eventually, we evaluate a series of metal- and carbon-based electrode materials to ensure enhanced Faradaic efficiency, consistent Se removal, and lower material costs. The results from this study will inform energy-efficient and cost-effective electrochemical approaches for Se remediation in various water and wastewater matrices.

Simultaneous Removal of Selenite and Selenate by Nanosized Zerovalent Iron in Anoxic Systems: The Overlooked Role of Selenite.

The application of nanosized zerovalent iron (nZVI) for reductive immobilization of selenite (Se(IV)) or selenate (Se(VI)) alone has been extensively investigated. However, as the predominant species, Se(IV) and Se(VI) usually coexist in the environment. Thus, it is essential to remove both species simultaneously in the solution by nZVI. Negligible Se(VI) removal (∼7%) by nZVI was observed in the absence of Se(IV). In contrast, the Se(VI) was completely removed in the presence of Se(IV), and the removal rate and electron selectivity of Se(VI) increased from 0.12 ± 0.01 to 0.29 ± 0.02 h-1 and from 1% to 4.5%, respectively, as the Se(IV) concentration increased from 0.05 to 0.20 mM. Se(IV) was rapidly removed by nZVI, and Se(VI) exerted minor influence on Se(IV) removal. Se(IV) promoted the generation of corrosion products that were mainly composed of magnetite (26%) and lepidocrocite (67%) based on the Fe K-edge XANES spectra and k3-weighted EXAFS analysis. Fe(II) released during the Se(IV) reduction was not the main reductant for Se(VI) but accelerated the transformation of F(0) to magnetite and lepidocrocite. The formation of lepidocrocite contributed to the enrichment of Se(VI) on the nZVI surface, and magnetite promoted electron transfer from Fe(0) to Se(VI). This study demonstrated that Se(IV) acted as an oxidant to activate nZVI, thus improving the reactivity of nZVI toward Se(VI), which displays a potential application of nZVI in the remediation of Se(IV)- and Se(VI)-containing water.

Fabrication of ferrihydrite-loaded magnetic sugar cane bagasse charcoal adsorbent for the adsorptive removal of selenite from aqueous solution

Herein we report the fabrication of ferrihydrite-loaded magnetic sugar cane bagasse charcoal adsorbent (FH@Fe3O4@SCBC) by in-situ growth method, which was in turn applied for the adsorptive removal of Se(IV) from aqueous solution. The prepared adsorbents were characterized by SEM-EDS, BET, XRD, VSM, FT-IR, and XPS analyses, and the effect of reaction temperature and pH on Se(IV) removal rate was investigated. Experimental results revealed that the maximum concentration of released Fe ions (0.20 mg L−1) was lower than the WHO highest authorized standard value for Fe in drinking water (0.30 mg L−1) indicating that FH@Fe3O4@SCBC adsorbent has good stability. Experimental results of adsorption kinetics and isotherms revealed that adsorption of Se(IV) by FH@Fe3O4@SCBC mainly occurred via chemisorption and monolayer adsorption and the maximum theoretical adsorption capacity Se(IV) was 95.15 mg g−1. The experiment on the coexisting anions showed that SO42− and PO43− exhibited a significant effect on the adsorption process of Se(IV) while Cl− and NO3− exhibited an insignificant effect. A proposed adsorption mechanism showed that Se(IV) removal included FH@Fe3O4@SCBC inner-sphere complexation, electrostatic interaction, and reduction reaction. According to VSM analysis, FH@Fe3O4@SCBC showed enhanced magnetic response thus facilitating its efficient and facile magnetic separation. Furthermore, FH@Fe3O4@SCBC realized minimal loss in adsorption activity (decreased by 11.5 %) after 10 consecutive reuses. This study provides a facile and cost-effective approach for the fabrication of highly stable FH@Fe3O4@SCBC adsorbent with high adsorption capacity, fast magnetic separation, and excellent recycling advantages making it a promising material for the remediation of Se(IV) from wastewater.

Remediation of selenium-contaminated soil through combined use of earthworm Eisenia fetida and organic materials

Selenium (Se)-polluted soils pose serious threats to terrestrial ecosystems through food chains. This study evaluated the use of earthworm Eisenia fetida and organic materials for Se remediation. The greater mortality (6.7%) and weight loss (28.6%) were observed for earthworms exposed to selenate than selenite at 20 mg Se Kg−1 over 21 d, while selenate was taken up 2.5-fold faster than selenite. Compared with peat moss, Se accumulation increased by 119% in selenite-exposed earthworms supplied with cow manure. Earthworm activity caused greater reduction in selenite (17.4%), with little impact on selenate-treated soil. X-ray absorption spectroscopy speciation analysis shows 87–91% of tissue Se was transformed to organo-Se, i.e., SeMet and SeCys, in earthworms exposed to either selenite or selenate, posing great risks to their predators. The study also found selenium increased bacterial diversity in earthworm casts, while greater relative abundances (~37.57%) of functional genera were obtained for selenite. Over 24 h, two bacteria strains, Bacillus cereus and Aeromonas encheleia, isolated from casts, rapidly reduced selenite by ~94%, compared to ~25% for selenate. Elemental Se was present only in strains (~27%), casts (~11%) and worm-inhabited soil (~2.7%) of selenite treatments, suggesting earthworm gut microbiota could buffer earthworms and other soil fauna from selenite toxicity.

Fungal Bioremediation of Selenium-Contaminated Industrial and Municipal Wastewaters.

Selenium (Se) is an essential element for most organisms yet can cause severe negative biological consequences at elevated levels. The oxidized forms of Se, selenate [Se(VI)] and selenite [Se(IV)], are more mobile, toxic, and bioavailable than the reduced forms of Se such as volatile or solid phases. Thus, selenate and selenite pose a greater threat to ecosystems and human health. As current Se remediation technologies have varying efficiencies and costs, novel strategies to remove elevated Se levels from environments impacted by anthropogenic activities are desirable. Some common soil fungi quickly remove Se (IV and VI) from solution by aerobic reduction to solid or volatile forms. Here, we perform bench-scale culture experiments of two Se-reducing Ascomycota to determine their Se removal capacity in growth media conditions containing either Se(IV) or Se(VI) as well as in Se-containing municipal (∼25 μg/L Se) and industrial (∼2000 μg/L Se) wastewaters. Dissolved Se was measured throughout the experiments to assess Se concentration and removal rates. Additionally, solid-associated Se was quantified at the end of each experiment to determine the amount of Se removed to solid phases (e.g., Se(0) nanoparticles, biomass-adsorbed Se, or internal organic selenoproteins). Results show that under optimal conditions, fungi more efficiently remove Se(IV) from solution compared to Se(VI). Additionally, both fungi remove a higher percentage of Se from the filtered municipal wastewater compared to the industrial wastewater, though cultures in industrial wastewater retained a greater amount of solid-associated Se. Additional wastewater experiments were conducted with supplemental carbohydrate- or glycerin-based carbon products and additional nitrogen- and phosphorous-containing nutrients in some cases to enhance fungal growth. Relative to unamended wastewater experiments, supplemental carbohydrates promote Se removal from municipal wastewater but minimally impact industrial wastewater removal. This demonstrates that carbon availability and source impacts fungal Se reduction and removal from solution. Calculations to assess the leaching potential of solid-associated Se from fungal biomass show that wastewater Se release will not exceed regulatory limits. This study highlights the considerable potential for the mycoremediation of Se-contaminated wastewaters.

Selenium removal and biotransformation in a floating-leaved macrophyte system

Selenium (Se) is an essential micronutrient for animals with a relatively narrow margin between essentiality and toxicity. To evaluate Se removal efficiency by a constructed wetland treatment system and its potential eco-risk, a floating-leaved macrophyte system was constructed, consisting of three main trophic levels. Over 21-d treatment, water Se concentration was gradually reduced by 40.40%, while 24.03% and 74.41% of the removed Se were found in the plant Nymphoides sp. and sediment, respectively. Among plant tissues, roots accumulated the highest Se level, although the greatest total Se was found in stems, followed by leaves, roots and rhizomes. X-ray absorption spectroscopy revealed that 82.65% of the absorbed selenite by the plants was biotransformed to other forms, as organo-Se species accounted for 45.38% of the Se retained in the sediment, which was primarily responsible for the entry of Se into the detritus food chain. The proportion of organo-Se compounds increased with trophic levels from sediments to fish, indicating, instead of direct uptake of selenite, the food chain transfer and biotransformation of Se may serve as a key exposure route for Se in aquatic organisms. When exposed to organo-Se compounds, i.e., SeCys and SeMet, the plants, shrimp and fish tended to accumulate more Se. However, the greater trophic transfer factor was obtained for selenate, leading to higher Se levels accumulated in fish. Overall, in addition to key mechanisms involved in Se removal, our research also provides a much better understanding of the potential eco-risk that may be posed by the floating-leaved plant system for bioremediation of Se via food chain transfer and biotransformation, paving the way for a low eco-toxic treatment system for Se remediation.

In Situ Preparation of Stabilized Iron Sulfide Nanoparticle-Impregnated Alginate Composite for Selenite Remediation.

Iron sulfide (FeS) nanoparticles have been applied for selenite (Se(IV)) remediation in recent decades. However, the easy aggregation and oxidization of FeS hamper their reactivity. In this study, in situ immobilization technology was applied to prepare FeS nanoparticle-impregnated alginate composite (FeS-SA) for Se(IV) remediation. FeS-SA removed 100% of the Se(IV) (0.13 mM), whereas pure nonstabilized FeS and sodium alginate (SA) beads eliminated only 27 and 20% of the Se(IV), respectively. The removal efficiency increased to 73% when pure stabilized FeS was used. Therefore, FeS-SA showed superior removal efficiency that was comparable with the joint effect of pure stabilized FeS and SA beads due to the homogeneous distribution of FeS in SA matrix. Furthermore, minor differences were established in the oxidation retardation effect of FeS exerted by SA beads under anoxic and oxic conditions. The biogenic regenerated FeS-SA still showed 40% removal efficiency for Se(IV) after five cycles due to the Fe leaching. XPS technique combined with the reference compounds and electron balance revealed that FeSe and metal selenium were the main selenium species after treatment. This in situ preparation of stabilized FeS-SA exhibited an excellent application prospect in the remediation of Se(IV).

Assessing best management practices for remediation of selenium loading in groundwater to streams in an irrigated region

Summary Selenium (Se) contamination in groundwater and surface water in numerous river basins worldwide has become a critical issue in recent decades. An essential micro-nutrient, Se can prove harmful to fish, water fowl, livestock, and even humans at elevated concentrations. In an overall effort to curb Se contamination in environmental systems, this study aims to identify best-management practices (BMPs) that can assist in remediating Se contamination in irrigated river basins. Using multi-decadal simulations of a calibrated and tested groundwater flow model (MODFLOW-UZF) and Se chemical reactive transport model (UZF-RT3D), the impact of water- and land-management strategies in reducing Se contamination are explored for a 500 km2 study region in the Lower Arkansas River Valley (LARV) in southeastern Colorado. The effectiveness of reduced applied irrigation volumes, sealing of earthen irrigation canals, rotational fallowing of cultivated land, reduced fertilizer loading, and enhanced riparian buffer zones, implemented individually as well as concurrently in various combinations, is explored. Results indicate that significant (>10%) decreases in Se mass loading to the Arkansas River system (main stem and tributaries) can be achieved when individual BMPs are implemented, with land fallowing, reduced irrigation, and enhanced riparian buffer zones providing the best results (13–14% load reduction). Even greater impacts (20–50% Se load reduction) can be achieved with 3 or 4 BMPs implemented concurrently. Results demonstrate that Se remediation can potentially be achieved within the LARV, and also can serve as a guide for other Se-affected river basins within the western United States and throughout the world.

Selenate and molybdate alter sulfate transport and assimilation in Brassica juncea L. Czern.: Implications for phytoremediation

The interaction of selenate and molybdate with the transport and assimilation of sulfate, and the effect of S on Se and Mo accumulation were investigated in Brassica juncea. Plants were supplied with different combinations of S and Se, or S and Mo for 24 h, and selenate and molybdate were given to plants at concentrations (200 μM) equal to that of sulfate in the S-sufficient condition. Se and Mo significantly reduced the plant growth. In S-sufficient plants, Se and Mo decreased sulfate uptake rate (at 24 h), and Se repressed the expression of the sulfate transporter BjSultr2.1. This effect was different from the one we observed for sulfate, which rapidly inhibited the sulfate uptake rates in +S plants. In S-starved plants, Se, Mo and S repressed sulfate uptake immediately (after 10 min), and the concomitant down-regulation of BjSultr2.1 occurred only in roots of plants treated with S. In plants exposed to Se or Mo the root expression of BjSultr2.1 was repressed later, after 6 h. S-starved plants accumulated significantly more Se and Mo than S-sufficient plants, likely due to the lack of competition of molybdate or selenate with sulfate for the transport through the same carriers. The up-regulation of the molybdenum transporter ( MOT1) gene expression could explain the higher amount of Mo than Se measured in the plant tissues. Se and Mo reduced the levels of cysteine (Cys) and glutathione (GSH) in +S plants, but increased the amount of these non-protein thiols in −S plants. The increase of GSH content in −S + Se plants was likely responsible for the down-regulation of the selenium binding protein ( SBP1) gene, while the induction of SBP1 observed in +S plants was mainly due to Se toxicity. The up-regulation of SBP1 was also evidenced in plants exposed to Mo, regardless of S availability and GSH content. Our results give better insight into plant uptake mechanisms for Se and Mo, and also have implications for phytoremediation. The interactions between sulfate and selenate or molybdate must be carefully considered when plants are employed for the remediation of Se- or Mo-contaminated sites, as the accumulation of the two contaminants in plants might be altered by the sulfate concentration in the growing medium.

Removal of selenite from wastewater using microbial fuel cells

Simultaneous electricity generation and selenium removal was evaluated in single-chamber microbial fuel cells (MFCs) with acetate and glucose as carbon sources. Power output was not affected by selenite up to 125 mg l(-1) with glucose as substrate. Coulombic efficiencies of MFCs with glucose increased from 25% to 38% at 150 mg Se l(-1). About 99% of 50 and 200 mg Se l(-1) selenite was removed in 48 and 72 h for MFCs fed with acetate and glucose, respectively, demonstrating the potential of using MFC technology for Se remediation.

Utilizing geochemical, hydrologic, and boron isotopic data to assess the success of a salinity and selenium remediation project, Upper Colorado River Basin, Utah

Stream discharge and geochemical data were collected at two sites along lower Ashley Creek, Utah, from 1999 to 2003, to assess the success of a site specific salinity and Se remediation project. The remediation project involved the replacement of a leaking sewage lagoon system that was interacting with Mancos Shale and increasing the dissolved salinity and Se load in Ashley Creek. Regression modeling successfully simulated the mean daily dissolved salinity and Se loads ( R 2 values ranging from 0.82 to 0.97) at both the upstream (AC1) and downstream (AC2/AC2A) sites during the study period. Prior to lagoon closure, net gain in dissolved-salinity load exceeded 2177 metric tons/month and decreased after remediation to less than 590 metric tons/month. The net gain in dissolved Se load during the same pre-closure period exceeded 120 kg/month and decreased to less than 18 kg/month. Sen's slope estimator verified the statistical significance of the modeled reduction in monthly salinity and Se loads. Measured gain in dissolved constituent loads during seepage tests conducted during September and November 2003 ranged from 0.334 to 0.362 kg/day for dissolved Se and 16.9 to 26.1 metric tons/day for dissolved salinity. Stream discharge and changes in the isotopic values of delta boron-11 ( δ 11B) were used in a mixing model to differentiate between constituent loadings contributed by residual sewage effluent and naturally occurring ground-water seepage entering Ashley Creek. The majority of the modeled δ 11B values of ground-water seepage were positive, indicative of minimal seepage contributions from sewage effluent. The stream reach between sites S3 and AC2A contained a modeled ground-water seepage δ 11B value of − 2.4‰, indicative of ground-water seepage composed of remnant water still draining from the abandoned sewage lagoons.

Acceleration of selenium volatilization in seleniferous agricultural drainage sediments amended with methionine and casein

Phytoremediation is potentially effective for managing excessive selenium (Se) in drainage sediment residing in the San Luis Drain in central California. This 2-year field study examined the feasibility of amending drainage sediment (containing 4.78 μg Se g −1) with methionine and casein to enhance volatilization without or with vegetation of Sporobolus airoides. Results show that without organic amendments, rates of Se volatilization were less than 25 μg m −2 d −1 in all plots. After amending the sediment with 71.4 mg methionine kg −1 soil, Se volatilization rates were 434 ± 107 μg m −2 d −1 in vegetated plots and 289 ± 117 μg m −2 d −1 in irrigated bare plots. With the amendment of 572 mg casein kg −1 soil, rates increased to 346 ± 103 μg m −2 d −1 in irrigated bare plots and to 114 ± 55 μg m −2 d −1 in vegetated plots. Both methionine and casein promoted biological remediation of Se via volatilization most effectively during the warmest months.

Phyto-products may be essential for sustainability and implementation of phytoremediation

Interest in selenium pollution and remediation technology has escalated during the past two decades. Although not known to be essential for plants, selenium is essential but could be toxic for humans and animals, depending on its concentration. A major selenium controversy in the 1980's emerged in California when the general public and scientific community became aware of selenium's potential as an environmental contaminant. After extensive research on several strategies to reduce loads of mobile Se for entering the agricultural ecosystem a plant-based technology, defined as ‘phytoremediation’ received increasing recognition, as a low-cost environmentally friendly approach for managing soluble Se in the soil and water environment. Successful long-term field remediation of Se by plants is, however, dependent upon acceptance and widespread use by growers, who are also concerned about potential commercial value from using the plant-based technology. Obtaining products with economic value from plants used in the cleanup of soil would certainly be an additional benefit to phytoremediation, which could help sustain its long-term use.

Selenium removal by constructed wetlands: quantitative importance of biological volatilization in the treatment of selenium-laden agricultural drainage water.

Management of selenium (Se) -contaminated agricultural drainage water is one of the most important environmental issues in California. To evaluate the feasibility of utilizing constructed wetlands to remediate Se-laden drainage water and the role of biological volatilization in Se removal, 10 flow-through wetland cells were constructed in 1996 in Corcoran, California. The monthly monitoring study from May 1997 to December 1999 showed that the vegetated wetlands were capable of significantly reducing Se from the inflow drainage water; an average of 69.2% of the total Se mass in the inflow was removed. Most of the Se was retained in sediment, and <5% of the Se was accumulated in plant tissues. Selenium volatilization was highest in the rabbitfoot grass wetland cell, where 9.4% of the Se input was volatilized over a 2-year period. Volatilization was greater in spring and summer than in fall and winter. For example, in May and June of 1998, 35 and 48%, respectively, of the Se entering the rabbitfoot grass cell was volatilized, whereas in the winter months, <5% was volatilized. The feasibility of using constructed wetlands for Se remediation, methods for the enhancement of Se volatilization, and the importance of considering potential Se ecotoxicity are discussed.