Evaluation of in Situ DGT Measurements for Predicting the Concentration of Cd in Chinese Field-Cultivated Rice: Impact of Soil Cd:Zn Ratios

Abstract

DGT (diffusive gradients in thin-films) has been proposed as a tool for predicting Cd concentrations in rice grain, but there is a lack of authenticating data. To further explore the relationship between DGT measured Cd and concentrations in rice cultivated in challenging, metal degraded, field locations with different heavy metal pollutant sources, 77 paired soil and grain samples were collected in Southern China from industrial zones, a "cancer village" impacted by mining waste and an organic farm. In situ deployments of DGT in flooded paddy rice rhizospheres were compared with a laboratory DGT assay on dried and rewetted soil. Total soil concentrations were a very poor predictor of plant uptake. Laboratory and field deployed DGT assays and porewater measurements were linearly related to grain concentrations in all but the most contaminated samples where plant toxicity occurred. The laboratory DGT assay was the best predictor of grain Cd concentrations, accommodating differences in soil Cd, pollutant source, and Cd:Zn ratios. Field DGT measurements showed that Zn availability in the flooded rice rhizospheres was greatly diminished compared to that of Cd, resulting in very high Cd:Zn ratios (0.1) compared to commonly observed values (0.005). These results demonstrate the potential of the DGT technique to predict Cd concentrations in field cultivated rice and demonstrate its robustness in a range of environments. Although, field deployments provided important details about in situ element stoichiometry, due to the inherent heterogeneity of the rice rhizosphere soils, deployment of DGT in dried and homogenized soils offers the best possibility of a soil screening tool.

Spatial Heterogeneity and Kinetic Regulation of Arsenic Dynamics in Mangrove Sediments: The Sundarbans, Bangladesh

“…11 Here the cylindrical DGTs (exposure window 2.54 cm 2 ) were pushed gently and smoothly into the sediment to 5-cm depth and covered with sediment, then removed 24 h later. 15 This was the first in situ deployment of DGT in Bangladesh soil.…”

Repeated phytoextraction of four metal-contaminated soils using the cadmium/zinc hyperaccumulator Sedum plumbizincicola

“…It mimics the processes of metal uptake by plants that occur in the rhizosphere including soil solution metal re-supply from the solid phase at the time scale of plant metal uptake (Davison et al, 2000). The DGT technique has been used for several decades to study metal bioavailability and good correlations have been obtained between metal measured by DGT and metal in metal-tolerant plants or crops (Song et al, 2004;Tandy et al, 2011;Williams et al, 2012). Luo et al (2010) found that metal measured by DGT is well correlated with metal in hyperaccumulators growing in soils with a series of added metal concentrations.…”

Reducing greenhouse gas emissions and grain arsenic and lead levels without compromising yield in organically produced rice

“…The common safety threshold of Pb and Cd is set at 200 μg kg −1 for rice grain (SCOOP, 2004;Chinese Food Standards Agency, 2005;FAO/WHO, 2011). Although the total grain Pb and Cd concentrations in the present study were always below the safety threshold limit, e-AWD might potentially help to reduce the Pb content in areas that have problems with this metal, as previous studies have shown that uptake of these metals in rice grain in the polluted areas can dangerously exceed the recommended safety limit, rising to as much as 1.00 mg kg −1 (Liu et al, 2003;Cheng et al, 2006;Fangmin et al, 2006;Yang et al, 2006;Fu et al, 2008;Williams et al, 2009Williams et al, , 2012Liu et al, 2013a,b).…”