Investigation of potential interferences on the measurement of dissolved reactive phosphate using zirconium oxide-based DGT technique

A diffusive gradients in thin films （DGT） technique based on hydrous zirconium oxide （Zr-oxide） has been recently developed for the measurement of dissolved reactive phosphate （DRP）. In this study, the detailed performance of the DGT technique is reported. Spiking experiments revealed that several orthophosphate monoester compounds contributed to the Zr-oxide DGT measurements of DRP. However, such a phenomenon is unlikely to occur during field conditions due to the low concentration of organic P in typical natural waters. The presence of Cl- （up to 106 g/L）, SO42- （up to 16 g/L）, HCO3- （up to 817 g/L）, and AsO2- and AsO 3 4 （both up to 1 mg As/L） in solutions had negligible effects on the measurement of DRP. The threshold concentrations of Cl-, SO42- and HCO3- have been increased from previous reports for the measurements of DRP using other adsorbent-based DGT techniques. The capacity for DGT measurements of DRP decreased with increasing solution pH （4.2-9.2）. The lowest capacity （95 μg P/m2 at pH 9.2） was still greater than that of other DGT techniques that are usually used for the measurement of DRP （2-12 μg P/cm2 ）. The Zr-oxide binding gel could be stored for up to 2 years without any aging effect. This period of validity was considerably longer than the ferrihydrite binding gel that is commonly used in present DGT devices （6 months）. The field application revealed that the concentrations of DRP measured in three fresh water samples using the Zr-oxide DGT technique were in agreement with those of the traditional colorimetric method.

Effect of water-driven changes in rice rhizosphere on Cd lability in three soils with different pH

Pot experiments were conducted to evaluate the effect of water management,namely continuous flooding(CF),intermittent flooding(IF)and non-flooding(NF),on Cd phytoavailaility in three paddy soils that differed in p H and in Cd concentrations.Diffusive gradients in thin films(DGT)technique was employed to monitor soil labile Cd and Fe concentrations simultaneously at three growth stages(tillering,heading and mature stage)of rice.The Cd phytoavailability were generally in the order of NF>IF>CF,and higher rice Cd(over permitted level,0.2 mg/kg)were only found in neutral and acidic soils under NF conditions.DGT measured soil labile Cd rather than total Cd was the most reliable predictor for Cd accumulation in rice.CF enhanced the formation of root plaques,which related to oxidation of large quantities of available Fe on root surfaces due to the O2 secretion of rice root.The Cd concentration in root plaques shared the same trend with DGT-Cd.Generally,root plaques would inhibit Cd uptake by rice under CF conditions,while under IF and NF conditions,root plaques act as a temporarily store of Cd,and soil labile Cd is the key factor that controls the transfer of Cd from soil to rice.The results of principle component analysis revealed that water management had the greatest effect on soil Cd lability and rice Cd in acidic soil.Thus,it is important to consider the availability of Cd and soil p H when assessing current agricultural practices of contaminated soil in China.