DGT and selective extractions reveal differences in arsenic and antimony uptake by the white icicle radish (Raphanus sativus).

Increasing soil contamination of arsenic (As) and antimony (Sb) is posing a serious concern to human health. Due to insufficient studies on Sb, the biogeochemical behaviour and plant uptake of Sb are assumed to be similar to that of As. As part of extensive research unravelling As and Sb biogeochemistry and plant uptake, the diffusive gradients in thin films (DGT) technique and sequential extraction procedure (SEP) were applied to evaluate As and Sb uptake by the white icicle radish (Raphanus sativus) cultivated in diluted cattle dip soils contaminated with As only and diluted mining soils contaminated with both As and Sb under agricultural conditions. Labile As and Sb in these soils measured by DGT (CDGT), soil solution (Csol), and SEP (CSEP-labile), were compared with As and Sb bioaccumulation in R. sativus tissues. Regardless of contamination sources and measurement techniques, the results showed that As was consistently more labile than Sb although total As concentrations in two soil types were lower than total Sb. Labile As in cattle dip soils was higher than that in mining soils, although there were no significant differences in soil As concentrations. The analysis of R. sativus tissues revealed that the overall As bioaccumulation was 4.5-fold higher than for Sb, and that As translocation to shoots was limited. In contrast, considerable Sb translocation to shoots was observed. The As and Sb bioaccumulation were strongly correlated with their CSEP-labile, CDGT, and Csol (R2 = 0.87-0.99), demonstrating the effectiveness of these techniques in predicting As and Sb in the white icicle radish. Compared with the cherry bell radish previously studied, the white icicle radish exhibited higher bioaccumulation factors (BAF) for Sb, but lower BAF for As, and lower translocation of As and Sb to shoots, providing understanding of how As and Sb are accumulated by radish cultivars.

An evaluation of ferrihydrite- and Metsorb™-DGT techniques for measuring oxyanion species (As, Se, V, P): effective capacity, competition and diffusion coefficients.

This study investigated several knowledge gaps with respect to the diffusive gradients in thin films (DGT) technique for measurement of oxyanions (As(III), As(V), Se(IV), Se(VI), PO4(3-), and V(V)) using the ferrihydrite and Metsorb™ binding layers. Elution efficiencies for each binding layer were higher with 1:20 dilutions, as analytical interferences for ICP-MS were minimised. Diffusion coefficients measured by diffusion cell and by DGT time-series experiments were found to agree well and generally agreed with previously reported values, although a range of diffusion coefficients have been reported for inorganic As and Se species. The relative binding affinity for both ferrihydrite and Metsorb™ was PO4(3-) ≈ As(V)>V(V) ≈ As(III)>Se(IV) >>> Se(VI) and effective binding capacities were measured in single ion solutions, and spiked synthetic freshwater and seawater, advising practical decisions about DGT monitoring. Under the conditions tested the performance of both ferrihydrite and Metsorb™ binding layers was directly comparable for As(V), As(III) Se(IV), V(V) and PO4(3-) over a deployment spanning ≤ 2 days for both freshwater and seawater. In order to return quantitative data for several analytes we recommend that the DGT method using either ferrihydrite or Metsorb™ be deployed for a maximum of 2 days in marine waters likely to contain high levels of the most strongly adsorbing oxyanions contaminants. The high pH, the competitive ions present in seawater and the identity of co-adsorbing ions affect the capacity of each binding layer for the analytes of interest. In freshwaters, longer deployment times can be considered but the concentration and identity of co-adsorbing ions may impact on quantitative uptake of Se(IV). This study found ferrihydrite-DGT outperformed Metsorb-DGT while previous studies have found the opposite, with variation in binding materials masses used being a likely reason. Clearly, preparation of both binding layers should always be optimised to produce the highest capacity possible, especially for seawater deployments.

DGT-induced copper flux predicts bioaccumulation and toxicity to bivalves in sediments with varying properties.

Many regulatory frameworks for sediment quality assessment include consideration of contaminant bioavailability. However, the "snap-shots" of metal bioavailability provided by analyses of porewaters or acid-volatile sulfide-simultaneously extractable metal (AVS-SEM) relationships do not always contribute sufficient information. The use of inappropriate or inadequate information for assessing metal bioavailability in sediments may result in incorrect assessment decisions. The technique of diffusive gradients in thin films (DGT) enables the in situ measurement of metal concentrations in waters and fluxes from sediment porewaters. We utilized the DGT technique to interpret the bioavailability of copper to the benthic bivalve Tellina deltoidalis in sediments of varying properties contaminated with copper-based antifouling paint particles. For a concentration series of copper-paint contaminated sandy, silty-sand, and silty sediment types, DGT-probes were used to measure copper fluxes to the overlying water, at the sediment-water interface, and in deeper sediments. The overlying water copper concentrations and DGT-Cu fluxes were shown to provide excellent exposure concentration-response relationships in relation to lethal effects occurring to the copper-sensitive benthic bivalve, T. deltoidalis. The study demonstrates the strength of the DGT technique, which we expect will become frequently used for assessing metal bioavailability in sediments.