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Remediation of Selenium-Polluted Soils and Waters by Phytovolatilization
Published in Norman Terry, Gary Bañuelos, of Contaminated Soil and Water, 2020
Adel Zayed, Elizabeth Pilon-Smits, Mark deSouza, Zhi-Qing Lin, Norman Terry
Some concerns have been expressed that biomethylation of Se may lead to the production of toxic forms of gaseous Se, or that Se may be redeposited in other areas to become toxic there. Dimethyl selenide is reported to be 500 to 700 times less toxic than selenate and selenite (LD50 of DMSe = 1600 to 2200 mg Se kg-1 rat; Wilber, 1980; Ganther et al., 1966; McConnell and Portman, 1952). Using a volatilization rate of 250 μg m-2 h-1 (an emission rate which would be promising for remediation), the highest 24-h average exposure of Se under stagnant conditions was computed to be 837 ng m-3 (Frankenberger and Karlson, 1988). An acceptable intake level documented by the EPA in guidance for Superfund sites is considered to be 3500 ng m-3, which is substantially higher than that calculated for Se biore-mediation. Furthermore, studies on the tropospheric transformation of DMSe on the west side of San Joaquin Valley, CA indicate that during the short lifetime of gaseous DMSe (9.6 days), the gas will be dispersed and diluted by air currents directly away from the contaminated areas, with deposition possibly occurring in the Se-deficient areas (Atkinson et al., 1990). At the highest annual deposition flux (4.5 g Se ha-1) mixed in the upper 10 cm of soil, the soil Se content would be increased by about 0.005 ppm (Frankenberger and Karlson, 1988).
Enhanced Biodegradation for On-Site Remediation of Contaminated Soils and Groundwater
Published in David J. Wilson, Ann N. Clarke, Hazardous Waste Site Soil Remediation, 2017
Ronald E. Hoeppel, Robert E. Hinchee
Selenium can be converted by microorganisms to several methylated compounds, especially dimethylselenide and dimethyldiselenide, which seem to have low toxicity. Unlike mercury, elemental selenium forms an insoluble precipitate (Reamer and Zoller, 1980). Dimethylselenide is the dominant methylated form, and although it readily sorbs to soils high in organic matter and clay (Zieve and Peterson, 1985), tilled soils and surface waters seem to show good release to the atmosphere (Thompson-Eagle and Frankenberger, 1990a; Frankenberger and Karlson, 1991). Aerobic conditions, high soluble selenium (selenate and selenite) concentrations, appropriate carbon amendments (glucose, pectin, and casein), and elevated temperatures (35 to 40°C) seem to promote the methylation process (Francis et al., 1974; Frankenberger and Karlson, 1991; Thompson-Eagle and Frankenberger, 1990b; Zieve and Peterson, 1981). Recent information indicates that orange peels plus inorganic nitrogen, zinc, cobalt (as methylcobalamin), and nickel supplementation promote volatilization. The main microorganisms responsible for methylation of selenium appear to be common mold fungi, including species of Penicillium, Acremonium, Aspergillus, Ulocladium, Fusarium, and Alternaria. These fungi prefer complex plant materials and proteins to simple carbon sources (Francis et al., 1974; Frankenberger and Karlson, 1991).
Selenium in soil-microbe-plant systems: Sources, distribution, toxicity, tolerance, and detoxification
Published in Critical Reviews in Environmental Science and Technology, 2022
Anamika Kushwaha, Lalit Goswami, Jechan Lee, Christian Sonne, Richard J. C. Brown, Ki-Hyun Kim
Methylation of Se is the primary process for Se volatilization from the soil (Lin & Terry, 2003). In soil, Se methylation takes place mostly through biological routes to yield less-toxic and volatile derivatives of Se (Vriens et al., 2016). Reaction rates are governed by the species present, microbial activity, OM, and various environmental conditions (e.g., temperature and soil water content). The presence of SeO32− in the soil can help increase the contents of Se in plant system. However, the Se levels do not accumulate in the soil because it is likely lost via volatilization. Selenide undergoes methylation reactions as follows: H2Se → CH3SeH → (CH3)2Se → (CH3)3Se+. However, end product of the methylation reaction is dimethyl selenide instead of trimethylselenomium (Ohta & Suzuki, 2008). Demethylation process is the removal of a methyl group and occurs under oxic and anoxic conditions.
Bioavailability of selenium in soil-plant system and a regulatory approach
Published in Critical Reviews in Environmental Science and Technology, 2019
Quang Toan Dinh, Mengke Wang, Thi Anh Thu Tran, Fei Zhou, Dan Wang, Hui Zhai, Qin Peng, Mingyue Xue, Zekun Du, Gary S. Bañuelos, Zhi-Qing Lin, Dongli Liang
Methylation is one of the key processes related to the volatilization and removal of Se from the soil (Lin et al., 2000; Lin & Terry, 2003). Methylation involves both chemical and biological mechanisms, but the biological process is dominate. Methylated and volatile derivatives of Se are formed and may be less toxic (Bolan et al., 2014; Winkel et al., 2015; Vriens, Behra, Voegelin, Zupanic, & Winkel, 2016). Previous studies showed that methylation reactions can occur from selenide as follows: H2Se → CH3SeH → (CH3)2Se → (CH3)3Se+ (Kremer, Ilgen, & Feldmann, 2005; Suzuki, Ohta, & Suzuki, 2006). Ohta and Suzuki (2008), however, suggested that the methylation reaction resulted in dimethyl selenide rather than trimethylselenonium as the end product. This result is likely due to the methylation reactions that are governed by the Se species present, microbial activity, OM, and various environmental conditions (e.g., temperature and soil water content) (Dungan & Frankenberger, 1999). Masscheleyn, Delaune, and Patrick (1991) showed that under moderately reducing or oxidizing conditions methylated Se compounds can be detected in reservoir sediments. Some studies have reported that bacteria, microalgae, fungi, and plants are capable of Se biomethylation (Terry, Zayed, de Souza, & Tarun, 2000; Neumann, De Souza, Pickering, & Terry, 2003).