Table 2.

Selected works observing the use of DGT to assess heavy metals mobility in soil and relations with different crops

Analyte	DGT type	Experimental conditions	Crops	Main findings	References
Cr, As, Cu, Zn, Cd, Pb	DGT with Zr-oxide-Chelex binding gel to measure labile metal(oid) concentration in soil	Soil from the rhizosphere of maize and wheat, and from these crops’ tissues were collected and analyzed. DGT, soil solution, EDTA, and total content methods were used to measure metal concentrations	Maize and wheat	Metal contents in soil, measured by DGT, were significantly correlated with their contents in the wheat and maize	Bai et al. (2023)
Zn	DGT with Chelex binding gel; polyacrylamide with agarose diffusive gel	Greenhouse experiment in lysimeters in which different amounts of ZnO nanoparticles were applied. DGT and chemical extractions were used to assess Zn availability	Cherry tomato and common bean	DGT technique was one the most appropriate methodologies for predicting the Zn availability in soil	Almendros et al. (2020)
Pb, Cu, Cd	DGT with Chelex binding gel	Soil samples contaminated at allowable limit with Pb, Cu, Cd, from agricultural soil treated with biochar and Delonix regia pods (2% w/w)	-	Dynamics of metals in contaminated soils is changed after treatment with amendments	Babalola and Zhang (2021)
Cd, Cr, Cu, Pb, Zn	DGT with Chelex binding gel	Industrially contaminated soil samples treated with natural zeolites (3 and 6 wt.%), incubated for 3 months. DGT was used to assess mobility and resupply from the solid phase	-	The resupply of Cd and Pb from the soil solid phase decreased in the samples amended by zeolite	Senila et al. (2022)
Cd	DGT with Chelex binding gel	Single and sequential (BCR) extractions together with DGT were used to predict Zn transfer to maize and release in soil	Maize	Bioavailable Cd concentration in soil assessed by DGT significantly correlated with the Cd accumulated in maize grains	Chen et al. (2021)
Cd	DGT with Chelex binding gel	Single chemical (CaCl2, DTPA, NH4NO3) extractions and DGT were employed to assess Cd bioavailability from amended soil to rice	Rice	The DGT-labile content of Cd in soil was well correlated to Cd content accumulated in brown rice	Luo et al. (2021)
Cd	DGT with binding gel (layered double hydroxide modified by DTPA and DTPA-LDHs)	Single and sequential chemical extractions, DGT, and bioindicator methods were used to assess Cd bioavailability in soils with different aging times	Barley	Cd bioavailability to barley was better evaluated by means of DGT compared with chemical extractions. Soil aging decreases Cd bioavailability	Ma et al. (2022)
Cd	DGT with Chelex binding gel with a dual-mode DGT holder, jointly with an agarose diffusive gel	Soils and vegetables sampled from greenhouse vegetable production systems. Total, CaCl2 extractable, and DGT-labile Cd concentrations were measured	Turnips and eggplants	DGT labile concentrations are independent of soil properties and may offer the possibility to obtain new soil thresholds in future research	Tian et al. (2018)
Cd	DGT with Chelex binding gel and polyacrylamide diffusive gel	Three water-management treatments (continuous flooding, intermittent flooding, and non-flooding) were compared to observe their effects on Cd phytoavailaility. DGT technique was utilized to display soil labile Cd and Fe	Rice	The Cd phytoavailability were generally in the order of non-flooding > intermittent flooding > continuous flooding. The Cd amount in roots experienced the same trend as DGT-Cd	Wang et al. (2020)
Cd	DGT with Chelex binding gel and agarose cross-linked polyacrylamide diffusive gel	Corresponding soil and plant samples were collected from different farms. Cd concentrations were measured in the plants, while in the soil four tests were applied to investigate the bioavailability of Cd: pseudo total, porewater, Ca(NO3)2-extracted, and DGT Cd concentrations	Spinach, potatoes, onion, wheat	Cd concentrations in soil measured by the different extractions were positively correlated to accumulation in crops. The extraction in Ca(NO3)2 well predicted Cd transfer in spinach leaves and onion, while DGT and porewater Cd better estimated the Cd transfer to potatoes and wheat grains	Yi et al. (2020)
As, Pb, Cd, Ni, Cu, Cr, Mn, Zn, Ba, U, REEs	DGT with Chelex binding gel	Multi-method evaluation of elements’ concentrations/fractionation/speciation in soils, based on sequential extraction (BCR), single extraction, and DGT	Corn	All techniques for available fraction assessment provided results well correlated to the metals accumulated in the corn plant, as compared to total metal contents.	Galhardi et al. (2020)
Cd, Cu, Pb, Zn	DGT with Chelex binding gel	DGT combined with BCR sequential extraction and bioaccessibility methods to estimate potential bioavailability and release of metals	-	Significant positive correlations obtained between the DGT and the bioaccessible fraction of metals	Li et al. (2023)
As, Cu, Zn	DGT with Chelex and with ferrihydrite binding layers	DGT was compared with other two analytical approaches (macrocolumn and microcolumn tests) to assess the changes in availability of Cu, Zn, and As in soil treated with different amendments	-	Microcolumn test was the fastest testing instrument to reveal the efficiency of amendments, while DGT is a good alternative to this, having less technical demands.	Manzano et al. (2019)
Cd, Pb, Zn	DGT with acrylamide monomer and allylagarose cross-linker as diffusive layer	DGT with a new type of diffusive gel was used to measure metal bioavailability in contaminated soil treated with sewage sludge under peppermint cultivation conditions	Peppermint	DGT compiled with 15% acrylamide and 0.3% allylagarose can substitute the original gel cross-linked with agarose to assess Cd, Pb, Zn mobility	Mohseni et al. (2021)
Zn	DGT with Chelex binding gel, agarose diffusive gel	Greenhouse experiment on contaminated soil treated with sorghum, poultry manure, and clover residues to assess changes in Zn bioavailable fraction using DGT, DTPA extraction, and bioassay	Corn	Application of organic fertilizers increases Zn effective concentration (measured by DGT), Zn extracted in DTPA, and plant Zn concentration. Sorghum residues decreased Zn effective concentration.	Mohseni et al. (2022)
As, P	DGT with cerium oxide resin gel	CeO2-DGT were deployed in four types of farmland soils over 400 h to study the interactions between P and As during their migration behaviors. These were coupled with dynamic DGT induced flux model in soils	-	The collected quantities of As in the DGT tools proved negative correlation with those of P, suggesting their competitive adsorption on soil solids	Ren et al. (2022)
Cd, Cr, Cu, Pb	DGT with Chelex binding gel	Greenhouse experiment on contaminated soil amended with biochar and compost, cultivated with lettuce. BCR sequential extraction, pore water extraction, and DGT were used to assess bioavailability of Cd, Cr, Cu and Pb and the effect of amendments on this	Lettuce	The amendment of soil with compost and biochar significantly decreases metal uptake by lettuce. DGT and the sequential extraction procedure results were better correlated with plant uptake than those from the pore water extraction and from total metal measurement	Turull et al. (2021)
Hg	DGT with open (polyacrylamide crosslinked with agarose) gel and restricted diffusive (polyacrylamide crosslinked with bis-acrylamide) gel layers; 3-mercaptopropyl-functionalized silica gel binding layer	Open and restricted diffusive gels to distinguish between inorganic and organic bioavailable Hg species in soil. The effective Hg concentration in soil was evaluated for predicting its uptake by lettuce in pot experiments	Lettuce	Linear relationships between the mass of Hg gathered in the resin gels and Hg concentration in the solution were obtained for both open and restricted gels. Hg concentrations in soil measured by DGT fitted well to the Hg concentration measured in lettuce roots.	Turull et al. (2019a)
Hg	DGT with open gel and restricted diffusive gel layers; 3-mercaptopropyl-functionalized silica gel binding layer	Greenhouse experiment on contaminated soil, amended with biochar and compost, and cultivated with lettuce. DGT with open gel and restricted diffusive gel used to measure organic and inorganic species	Lettuce	Added biochar lowers the bioavailability of Hg in soil and thus reduces the Hg uptake by lettuce. Inorganic Hg were the most abundant Hg species in soils, in all sets of the experiment	Turull et al. (2019b)
Hg	DGT with 3-mercaptopropyl-functionalized silica gel binding layer	Four species of vegetables and corresponding garden soils collected from four locations around a former mining area. Total Hg in soil and in vegetables, Hg in soil solution, and DGT-labile Hg fraction in soil were measured	Garlic, parsley, carrot, onion	The R ratio between Hg-DGT/Hgsoln (on average 0.75) suggested a high resupply probability of Hg from soil solid phase to the soil solution	Senila et al. (2023)