Volatilization: a soil degassing coefficient for iodine

Sheppard, Marsha I.; Thibault, D.H.; Smith, Paul A.; Hawkins, Janice L.

doi:10.1016/0265-931x(94)90072-8

Cited by 18 publications

(16 citation statements)

References 27 publications

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“…Volatilization of 129 I from solution is considered unlikely as such losses have been shown to be small in previous studies (e.g. Sheppard et al, 2004Sheppard et al, , 2006. Sorption of iodide and iodate to oxide phases is weak at pH > 6 where sorption to organic matter dominates (see e.g.…”

Section: Iodatementioning

confidence: 96%

Iodine dynamics in soils

Shetaya

Young

Watts

et al. 2012

Geochimica et Cosmochimica Acta

137

118

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We investigated changes in iodine ( 129 I) solubility and speciation in nine soils with contrasting properties (pH, Fe/Mn oxides, organic carbon and iodine contents), incubated for nine months at 10 and 20°C. The rate of 129 I sorption was greater in soils with large organic carbon contents (%SOC), low pH and at higher temperatures. Loss of iodide (I À ) from solution was extremely rapid, apparently reaching completion over minutes-hours; iodate (IO À 3 ) loss from solution was slower, typically occurring over hours-days. In all soils an apparently instantaneous sorption reaction was followed by a slower sorption process for IO À 3 . For iodide a faster overall reaction meant that discrimination between the two processes was less clear. Instantaneous sorption of IO À 3 was greater in soils with high Fe/Mn oxide content, low pH and low SOC content, whereas the rate of time-dependent sorption was greatest in soils with higher SOC contents. Phosphate extraction (0.15 M KH 2 PO 4 ) of soils, $100 h after 129 I spike addition, indicated that concentrations of sorbed inorganic iodine ( 129 I) were very low in all soils suggesting that inorganic iodine adsorption onto oxide phases has little impact on the rate of iodine assimilation into humus. Transformation of dissolved inorganic 129 IO À 3 and 129 I À to sorbed organic forms was modelled using a range of reactionand diffusion-based approaches. Irreversible and reversible first order kinetic models, and a spherical diffusion model, adequately described the kinetics of both IO À 3 and I À loss from the soil solution but required inclusion of a distribution coefficient (k d ) to allow for instantaneous adsorption. A spherical diffusion model was also collectively parameterised for all the soils studied by using pH, soil organic carbon concentration and combined Fe + Mn oxide content as determinants of the model parameters (k d and D/r 2 ). The kinetic model parameters were not directly related to a single soil parameter; inclusion of pH, SOC, oxide content and temperature was necessary to describe the observed behaviour. From the temperature-dependence of the sorption data the activation energy (E a ) for 129 IO À 3 transformation to organic forms was estimated to be $43 kJ mol À1 . The E a value was independent of %SOC and was consistent with a reaction mechanism slower than pore diffusion or physical adsorption, but faster than most surface reactions.

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Section: Iodatementioning

confidence: 96%

Iodine dynamics in soils

Shetaya

Young

Watts

et al. 2012

Geochimica et Cosmochimica Acta

137

118

View full text Add to dashboard Cite

show abstract

“…A shorter-term laboratory study with an organic soil gave a volatilization rate of 2 Â 10 ÿ10 s ÿ1 Degassing from soil (s ÿ1 ) 3Â 10 ÿ11 (10) 7 Â 10 ÿ10 (10) 0 0 0 Ingestion transfer coefficient from plants to terrestrial animal human-food products a AM (SD) indicates arithmetic mean (standard deviation) implying a normal distribution, GM (GSD) indicates geometric mean (geometric standard deviation) implying a lognormal distribution. (Sheppard et al, 1994). Less volatilization from organic soils would be expected because they often more effectively sorb iodine (Bostock et al, 2003).…”

Section: Degassing Of Iodine From Soilmentioning

confidence: 97%

“…The soil degassing rates used in Canadian assessments originally were lognormally distributed with a GM of 1 Â 10 ÿ9 s ÿ1 (0.032 a ÿ1 ) and a GSD of 10 (Sheppard, 1992), independent of the soil type. In a subsequent study , this value was reduced to a GM of 6.7 Â 10 ÿ10 s ÿ1 (0.021 a ÿ1 ) with a much smaller GSD of 3.0 based on the paper by Sheppard et al (1994). This GSD of 3.0 was a subjective estimate, taken as intermediate between a GSD of 1.9 from research done in the field on Canadian soils (Sheppard et al, 1994) and a GSD of 11 that included field values from the arid Hanford site in the US (Garland et al, 1987cited by Sheppard et al, 1994.…”

Section: Degassing Of Iodine From Soilmentioning

confidence: 99%

“…In a subsequent study , this value was reduced to a GM of 6.7 Â 10 ÿ10 s ÿ1 (0.021 a ÿ1 ) with a much smaller GSD of 3.0 based on the paper by Sheppard et al (1994). This GSD of 3.0 was a subjective estimate, taken as intermediate between a GSD of 1.9 from research done in the field on Canadian soils (Sheppard et al, 1994) and a GSD of 11 that included field values from the arid Hanford site in the US (Garland et al, 1987cited by Sheppard et al, 1994. Sheppard et al (1994) summarized much of the earlier literature, and the range of iodine loss rate constants was 6 Â 10 ÿ12 to 1 Â 10 ÿ7 s ÿ1 with a GM of 6.7 Â 10 ÿ10 s ÿ1 , the value used by Zach et al (1996).…”

Section: Degassing Of Iodine From Soilmentioning

confidence: 99%

“…Measurements done by Sheppard et al (1994) over three years in a field setting, using a vegetated mineral soil, indicated a loss rate by volatilization of 7 Â 10 ÿ9 s ÿ1 (GSD ¼ 1.4). A shorter-term laboratory study with an organic soil gave a volatilization rate of 2 Â 10 ÿ10 s ÿ1 Degassing from soil (s ÿ1 ) 3Â 10 ÿ11 (10) 7 Â 10 ÿ10 (10) 0 0 0 Ingestion transfer coefficient from plants to terrestrial animal human-food products a AM (SD) indicates arithmetic mean (standard deviation) implying a normal distribution, GM (GSD) indicates geometric mean (geometric standard deviation) implying a lognormal distribution.…”

Section: Degassing Of Iodine From Soilmentioning

confidence: 99%

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