Microbial Participation in Iodine Volatilization from Soils

Abstract

The roles of microorganisms in iodine volatilization from soils were studied. Soils were incubated with iodide ion (I-), and volatile organic iodine species were determined with a gas chromatograph. Iodine was emitted mainly as methyl iodide (CH3I), and CH3I emission was sometimes enhanced by the addition of glucose. Soils were then incubated with a radioactive iodine tracer (125I), and radioiodine emitted from soils was determined. The emission of iodine was enhanced in the presence of yeast extract but was inhibited by autoclaving of soils. The addition of streptomycin and tetracycline, antibiotics that inhibit bacterial growth, strongly inhibited iodine emission, while a fungal inhibitor cycloheximide caused little effect. Forty bacterial strains were randomly isolated from soils, and their capacities for volatilizing iodine were determined. Among these, 14 strains volatilized significant amounts of iodine when they were cultivated with iodide ion. Phylogenetic analysis based on 16S ribosomal DNA sequences showed thatthese bacteria are widely distributed through the bacterial domain. Our results suggest that iodine in soils is methylated and volatilized as CH3I by the action of soil bacteria and that iodine-volatilizing bacteria are ubiquitous in soil environments. The pathway of iodine volatilization by soil bacteria should be important for understanding the biogeochemical cycling of iodine as well as for the assessment of long-lived radioactive iodine (129I) in the environment.

Surficial redistribution of fallout131iodine in a small temperate catchment

“…2B). We propose that the discrepancy between 131 I inventories of deposition and accumulation is mechanistic rather than an artifact of sampling, and might be explained by three endmember processes: (i) Secondary deposition by an undetected (nonprecipitation) process, such as uptake or sorption of gaseous I 2 directly from the atmosphere (21) ; or, translocation of iodine from subsurface to surface soil via either (ii) root uptake (22) or (iii) volatilization (23,24) of iodine that, upon initial deposition, penetrated to soil depths greater than 2.5 cm. Details of the upward transport of volatilized iodine can include diffusion to surface soil and entrapment in the rhizosphere, or escape to the atmosphere with subsequent stomatal uptake (23) or redeposition from dew or fog (25) as in mechanism 1 above.…”

Biogeochemical Considerations Related To The Remediation Of I-129 Plumes

“…A survey of 53 soil samples collected from rice paddies, forests, upland fields, and wetlands yielded detectable CH 3 I production from spiked iodide (0.1 µM) in samples from each of these terrestrial environments (Amachi et al, 2003). Formation of other alkyl iodides was not observed.…”

Biofortificación con yodo en plantas para consumo humano

“…Este efecto parece depender de la habilidad de las sustancias húmicas para adsorber el yodo (proceso al parecer mediado por microorganismos) disminuyendo su volatilización (Bostock, 2003), si bien en ausencia de materia orgánica parece ocurrir gran actividad de volatilización de yodo en forma de CH3I a través de la actividad microbiana (Amachi et al, 2003). Este hecho pudiera explicar en parte la aparente relación negativa entre el contenido de arcillas del suelo y la absorción de…”

“…This effect seems to depend on the ability of humic substances to adsorb iodine (process apparently mediated by microorganisms) decreasing its volatilization (Bostock, 2003), although in the absence of organic matter seems to be great iodine volatilization activity as CH3I through microbial activity (Amachi et al, 2003). This fact may partly explain the apparent negative relationship between clay content of the soil and iodine uptake by plants, while soil pH does not appear to exert any effect in the range of 5.4 to 7.6 (Shinonaga et al, 2001).…”