Field-Scale Heterogeneity and Geochemical Regulation of Arsenic, Iron, Lead, and Sulfur Bioavailability in Paddy Soil

Abstract

A method using miniaturized arrayed DGT-probes (PADDI) for high-frequency in situ sampling with LA-ICPMS and CID analysis was developed to measure the field-scale heterogeneity of trace-element bioavailability. Robust calibrations (R2 > 0.99) combined with high-sensitivity (LOD = 0.35 ng cm–2), multielemental detection, and short measurement times were achieved using a new LA-ICPMS microDGT analysis. In the studied paddy-site (size: ∼2500 m2), total element concentrations across the field were approximately uniform (R.S.D. < 10%), but bioavailability was shown to vary significantly as determined from 864 microgel measurements housed within 72 PADDI arrays. Porewater As measurements were unable to differentiate the top/rhizosphere and bulk/deeper-soil layers. However, dynamic sampling with DGT revealed significant differences. Heterogeneity behaviors varied greatly between the different elements. Arsenic bioavailability was stable laterally across the field, but varied with depth, which was in contrast to the trends for Pb. Fe/S(−II) change was bidirectional, differing horizontally and vertically throughout the field. The heterogeneity in Pb bioavailability, due to the high frequency of hotspot maxima that were discretely dispersed across the paddy, proved the most difficult to simulate requiring the greatest number of probe deployments to determine a reliable field-average. The DGT-PADDI system provides a new characterization of infield trends for improved trace-inorganics’ management in agricultural wetlands.

Rice Rhizospheric Effects on the Bioavailability of Toxic Trace Elements during Land Application of Biochar

“…Even though Fe oxides can provide sorption sites for various cation elements, Cu has been reported to be preferentially absorbed by organic matter, such as humic substance. Regarding As, Fe (hydr)­oxides were the dominant reactive adsorption surface for As, but the disconnection between As and Fe has also been revealed in some previous studies that have shown that both porewater and DGT measurements of Fe and As were not significantly correlated in some paddy fields and laboratory tests. , This does not necessarily discount the importance of reductive dissolution of Fe in As mobilization, but it does highlight the importance of other factors, such as DOC and microorganism diversity, as controls for As mobilization dynamics. , …”

“…The laser was set up first with primary calibrations using the National Institute of Standards and Technology (NIST) glass standard 610. The LA-ICPMS system was optimized principally by adjusting gas flow rates, torch sampling depth, and radio frequency (RF) power to achieve the maximum signal intensity and stability of target elements while minimizing interferences . The instrumental parameters for analysis are listed in Table S3.…”

“…Rice, one of three main global crops, occupies more than 140 million hectares worldwide . TTE contamination in soils has increased the risk of TTE transfer and accumulation in rice grains. , With the increasing scale of biochar use, as a soil conditioner for the purposes of fertility improvement and organic carbon sequestration, the number of studies focusing on biochar treatments in paddy soils and their influences on TTE accumulation in rice grains has also followed suit. ,, Influences of biochar vary considerably with the pyrolysis temperature, feedstock material, application ratio, and soil physicochemical properties .…”

Localized Intensification of Arsenic Release within the Emergent Rice Rhizosphere

“…Indeed, the ploughed paddy topsoil does begin the cropping cycle relatively homogenized, but after flooding and overtime (0-4 months) the spatial diversity of the system increases greatly. 33 These initial first steps in solute interchange and soil surface interactions created by the emergent rhizospheres of the newly planted rice, are important because they create zones of localized enrichment/depletion in elemental bioavailability, forming different ecological niches (Figure 1), thus impacting plant uptake through diffusion and resupply. However, these gradients in porewater elements availability, later develop/establish into chemically stratified zones differing with more permanency in their solid phase composition and stoichiometry, such as is the case with Fe or Mn plaque aggregation.…”

Development and Applications of Novel DGT Passive Samplers for Measuring 12 Per- and Polyfluoroalkyl Substances in Natural Waters and Wastewaters

“…The diffusive gradients in thin-films (DGT) technique is an alternative and very well established passive sampler; it is based on Fick’s first law of diffusion and was originally invented for measuring inorganic substances in situ without field calibration. − DGT samplers can enrich the target analytes in situ, avoiding the potential errors caused by sample transportation and pretreatment of grab sampling. The measured data integrate exposure concentrations over the sampling time to provide a time-weighted average (TWA) concentration.…”