Indicator of Reduction in Soil (IRIS) devices: A review

Sapkota, Yadav; Duball, Chelsea; Vaughan, Karen; Rabenhorst, Martin C.; Berkowitz, Jacob F.

doi:10.1016/j.scitotenv.2022.158419

Cited by 7 publications

(4 citation statements)

References 47 publications

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“…An 11-week mesocosm study conducted by Vaughan et al (2016) also found that 0% S-added to native soils had the lowest percentage of FeS precipitation on IRIS devices, with a median of 0.2%, while 1% S-added had a median of 2.5% FeS precipitation, and 2.5% and 5% S-added displayed medians of 5.2% and 7.7% FeS precipitation, respectively. It is also important to acknowledge that FeS-precipitates can fade (i.e., disappear) from IRIS devices upon exposure to ambient air (i.e., oxidation), or if devices are installed in high sulfide environments (e.g., coastal soils) for longer periods (i.e., 1 day or more), it is possible for all of the Fe-oxide paint to be converted to FeS, which will no longer adhere to the PVC resulting in a white color that was not induced directly by the transformation of Fe 3+ to Fe 2+ exclusively (Rabenhorst et al, 2010;Duball et al, 2019;Duball et al, 2020;Sapkota et al, 2022). Regardless of these studies, there is no standard protocol that outlines approximately how long IRIS devices should be left in situ and it still remains unclear exactly how long it takes for FeS to precipitate on IRIS devices under strongly reducing conditions.…”

Section: Core Ideasmentioning

confidence: 99%

Rapid formation of iron monosulfide on Indicator of Reduction in Soil devices in S‐rich hydric soils

Duball

Andersen

Beaudette

et al. 2023

Soil Science Soc of Amer J

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Indicator of Reduction in Soil (IRIS) devices are used to identify anaerobic conditions in soils for hydric soil and wetland identification purposes. IRIS devices quantify anaerobic conditions via the visualization of iron (Fe) reduction (e.g., orange Fe 3+ paint reduces to soluble Fe 2+ , leaving behind the bare, white polyvinyl chloride device). Under stronger reducing conditions, sulfate (SO 4 2− ) reduction can occur, and sulfides (S 2− and/or H 2 S) can react with the Fe 3+ paint, resulting in the precipitation of black-colored, reduced iron monosulfide (FeS). While these processes are well known, the rate of FeS formation remains relatively understudied and current IRIS methods may not capture these data accurately. This study investigated FeS formation on IRIS films to identify deployment times that capture the minimum and maximum precipitation of FeS. To determine the timing and magnitude of FeS-precipitation on IRIS films, five replicate films were deployed in a wet, S-rich soil, across 11 periods ranging from 2 min to 30 days. Results show that FeS precipitated on IRIS films in just 2 min, and the highest average amount of FeS (82%) precipitated in 1 day. After 1 day, the percentage of FeS decreased and a white color change became more apparent on IRIS films. Our results suggest that the recommended 30-day deployment period is too long for accurately measuring FeS-precipitation on IRIS devices deployed in wet, alkaline soils. These considerations should be incorporated into standard IRIS protocols used to quantify anaerobic conditions and other biogeochemical conditions (e.g., pore-water sulfide levels) in S-rich soils. INTRODUCTIONWetlands provide valuable ecosystem services including water filtration, increased biodiversity, flood abatement, and provision of habitat for rare, endangered, and migratory species, among others. Wetland areas are typically identified based on a three-parameter approach requiring positive evidence of wetland hydrology,

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Section: Core Ideasmentioning

confidence: 99%

Rapid formation of iron monosulfide on Indicator of Reduction in Soil devices in S‐rich hydric soils

Duball

Andersen

Beaudette

et al. 2023

Soil Science Soc of Amer J

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“…When placed in contact with soil, the loss of the mineral paint is taken as an indication of conditions supporting microbial reduction of the mineral: between −200 and 0 mV at pH 7 for iron oxides (ferrihydrite and goethite) and 450–600 mV at pH 7 for manganese oxides (Levar et al., 2014). IRIS sensors are easy to assemble, deploy, and, presumably, to interpret—qualities that make them ideal for assessment of redox conditions in soil under field conditions (Sapkota et al., 2022).…”

Section: Introductionmentioning

confidence: 99%

“…Indicators of reduction in soil (IRIS) are used to assess redox conditions in soil simply and inexpensively (Park & Rabenhorst, 2018). The sensors consist of strips of polyvinyl chloride (PVC) coated with mineral paint (birnessite or iron oxyhydroxides; Sapkota et al., 2022). When placed in contact with soil, the loss of the mineral paint is taken as an indication of conditions supporting microbial reduction of the mineral: between −200 and 0 mV at pH 7 for iron oxides (ferrihydrite and goethite) and 450–600 mV at pH 7 for manganese oxides (Levar et al., 2014).…”

Section: Introductionmentioning

confidence: 99%

Potential interference of organic acids and ferrous iron in the interpretation of Fe and Mn indicators of reduction in soil

Loffredo

Rabenhorst

Stolt

et al. 2023

Soil Science Soc of Amer J

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Removal of manganese (Mn) and iron (Fe) oxide coatings from indicators of reduction in soil (IRIS) is considered a function of microbial reduction of these elements under sufficiently reducing conditions, but there may be situations where removal is abiotic. We examined whether abiotic removal of Mn and Fe oxide coatings may be facilitated by organic acids and whether loss of Mn can take place via chemical reduction by ferrous iron (Fe2+) in vitro. Loss of color from Mn‐IRIS in citric acid solution was highest at 1 and 10 mM regardless of pH, with no loss observed at lower concentrations. Effects of citric acid on Fe‐IRIS were also limited to 1 and 10 mM, but color loss only occurred at pH 4.5 and the rate and extent of loss were lower than for Mn‐IRIS. Color loss from Mn‐IRIS in oxalic acid was highest at 1 and 10 mM and increased with decreasing pH. Effects of oxalic acid on loss of color from Fe‐IRIS were limited to 1 and 10 mM. Loss of color from Mn‐IRIS was limited to 10 mM salicylic acid and pH 4.5, with no effect on Fe‐IRIS regardless of concentration and pH. Only the two highest concentrations of Fe2+ (50 and 100 mM) resulted in reduction of the Mn‐IRIS coating and subsequent deposition of an Fe oxide coating. Organic acids and pH have a differential effect on color loss from Mn‐ and Fe‐IRIS, with only high concentrations of organic acids at low pH possibly interfering with interpretation.

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“…For both Mn and Fe, the oxidized forms are practically insoluble, while the reduced forms are more soluble . Utilizing these redox reactions, indicators of reduction in soil (IRIS) devices were developed as a low-cost, in situ technique for observing reducing conditions in soil. − IRIS first used Fe oxides (ferrihydrite and goethite) coated on a PVC pipe . Under Fe-reducing conditions, the orange Fe coating reductively dissolves from the device, revealing the white PVC underneath.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the Mechanisms of Fe Oxidation and Mn Reduction on Mn Indicators of Reduction in Soil (IRIS) Films

Limmer

Linam

Evans

et al. 2023

Environ. Sci. Technol.

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Indicators of reduction in soil (IRIS) devices are low-cost soil redox sensors coated with Fe or Mn oxides, which can be reductively dissolved from the device under suitable redox conditions. Removal of the metal oxide coating from the surface, leaving behind the white film, can be quantified and used as an indicator of reducing conditions in soils. Manganese IRIS, coated with birnessite, can also oxidize Fe(II), resulting in a color change from brown to orange that complicates the interpretation of coating removal. Here, we studied field-deployed Mn IRIS films where Fe oxidation was present to unravel the mechanisms of Mn oxidation of Fe(II) and the resulting minerals on the IRIS film surface. We observed reductions in the Mn average oxidation state when Fe precipitation was evident. Fe precipitation was primarily ferrihydrite (30−90%), but lepidocrocite and goethite were also detected, notably when the Mn average oxidation state decreased. The decrease in the average oxidation state of Mn was due to the adsorption of Mn(II) to the oxidized Fe and the precipitation of rhodochrosite (MnCO 3 ) on the film. The results were variable on small spatial scales (<1 mm), highlighting the suitability of IRIS in studying heterogeneous redox reactions in soil.Mn IRIS also provides a tool to bridge lab and field studies of the interactions between Mn oxides and reduced constituents.

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Indicator of Reduction in Soil (IRIS) devices: A review

Cited by 7 publications

References 47 publications

Rapid formation of iron monosulfide on Indicator of Reduction in Soil devices in S‐rich hydric soils

Rapid formation of iron monosulfide on Indicator of Reduction in Soil devices in S‐rich hydric soils

Potential interference of organic acids and ferrous iron in the interpretation of Fe and Mn indicators of reduction in soil

Unraveling the Mechanisms of Fe Oxidation and Mn Reduction on Mn Indicators of Reduction in Soil (IRIS) Films

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