The Establishment And Application Of DGT Passive Sampling Technology For Thallium In Water

As a highly toxic trace metal,thallium?Tl? was defined as a priority pollutant.Because the chemical species of elements may be changed with sampling,transportation and storage,accurate measurement of elements' concentration by active sampling method was a great challenge.As an in situ passive sampling method,technique of Diffusive Gradients in Thin-films?DGT? can measure the average concentration of target elements in a certain time.In this study,a kind of manganese dioxide??-MnO₂?was used as binding gel and deployed to a new DGT device.Combined with the conventional Chelex-DGT device,?-MnO₂-DGT was characterized to measure the concentration of Tl???? and Tl??? species? in water.The diffusion coefficients?D? of Tl??? and Tl??? were measured for the first time in this study.D of Tl??? and Tl??? were 14.74 × 10-6 cm2 s-1 and 9.02 × 10-6 cm2 s-1,respectively,at 25?.The adsorption kinetics of Tl by Chelex and ?-MnO₂ binding gels showed that Tl could be adsorb by ?-MnO₂ gel,rapidly and effectively,however,the uptake of Tl by Chelex gel was poor?only 23%²5%?.1 mol L-1oxalic acid was used to elute Tl on the ?-MnO₂ gels,the elution efficiencies of Tl??? and TI??? were 1.04 ± 0.06 and 0.86 ± 0.06,respectively.Moreover,1 mol L-1HNO3 was used to remove Tl on the Chelex gels,and achieved elution efficiencies of 0.85 ± 0.09 and 0.76 ± 0.05,respectively.?-MnO₂-DGT was proved to be effective used at the aqueous solution of p H?4–9?,ionic strength?0.1–200 mmol L-1NaNO₃? and organic matter?0–30 mg L-1?.The method detection limit of ?-MnO₂-DGT to Tl??? and Tl??? were < 2.0 ng L-1.However,Chelex-DGT is greatly affected by environmental conditions and can not effectively monitoring Tl in water.Adsorption capacity of ?-MnO₂-DGT was 27.1 ?g cm-2 and the storage time for the gel was at least 117 d,which confirmed good performance for long-term monitoring of Tl.The ?-MnO₂-DGT device was deployed in the natural water of the Xijiang River.The monitoring results showed that the field sampling trial was affected by the dynamic system,the Tl concentration of grabbing sampling measured at the different time was quite different.Besides,the ?-MnO₂-DGT device can accurately measure the time-averaged concentration of Tl,and the in-situ measurement avoids the change of chemical species of target elements.It's reported that the DGT-labile metal species was considered more effectively represent the potential bioavailable fraction.The ?-MnO₂-DGT and Chelex-Metsorb-DGT devices were deployed in the natural water of Shaoguan section of the Beijiang River.The health risks of the heavy metals in the river were evaluated by combining the active and passive sampling methods.The results showed that most of the elements measured were below the Water Quality Standards for Drinking Water?GB5749-2006? in China.Correlation analysis showed Tl and the other elements in the river were mostly affected by mining areas and industries but not sources like domestic waste and agricultural non-point pollutant.Health risk assessment showed that heavy metals haven't potential non-carcinogenic risks to human,and the pollution status of these trace metals in Shaoguan section of the Beijiang River was generally at an acceptable level.The ?-MnO₂-DGT device can in situ monitor the concentration of Tl in water and avoid the change of Tl speciation during sampling or transportation.?-MnO₂-DGT can also effectively monitor the average Tl concentration in a certain time range.In the future,the?-MnO₂-DGT device can also be put into wider applications.In summary,the newly developed ?-MnO₂-DGT shows potential for environmental monitoring and biogeochemical investigation of Tl in waters.