Wu, Shuang and Zhang, Hao (2017) Development of a rapid screening technique for contaminants in environmental monitoring and regulation. PhD thesis, Lancaster University.
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Abstract
Rapid screening technique is important and efficient for routine monitoring of chemical pollutants, risk assessment and decision making in dealing with contaminants in waters and soils. The focus of this thesis is on developing simple and rapid screening methods based on the diffusive gradients in thin films (DGT) technique to assess the concentration of phosphorus and metals qualitatively and quantitatively. Firstly, a rapid detection technique for phosphorus based on Metsorb DGT devices and a colour imaging method using the conventional molybdenum blue were developed and fully tested under different conditions. The fully quantitative interpretation of the P concentration can be assessed in the linear range of 0.1 to 1.02 μg cm-2 device that corresponds to the concentration range of 9 to 98 μg L-1 if the deployment time is 24 hours and the water temperature is 20oC. Secondly, digital colorimetric analysis using a flat-bed scanner was utilised to quantify the Cu, Ni, and Co in water following the DGT uptake of metals by Chelex resin gel without involving further reactive reagents. The fully quantitative interpretation of the Cu, Ni, and Co concentration can be assessed in the linear range of 1.5 to 165 μg cm-2 , 2.7 to 153 μg cm-2 , and 1.6 to 159.2 μg cm-2 , respectively, which correspond to the concentration range of 0.05 to 5 mg L-1 for all three metals if the deployment time is 24 hours and the water temperature is 20oC. Thirdly, a rapid screening technique for Cr(VI) using DGT and a high-resolution CID base on the surface colouration of the N-Methyl-D-glucamine (NMDG) binding gel has been developed. The relationship between the accumulation of Cr(VI) in NMDG gels and the corresponding change in grayscale intensity was well fitted using a quintic polynomial. The fully quantitative interpretation of the Cr(VI) concentration can be assessed in the linear range of 0.31 to 2.47 μg cm-2 which correspond to the concentration range of 12.5 to 150 μg L-1 if the deployment time is 24 hours and the water temperature is 20oC. This study has formulated a DGT deployment guide list to determine whether the concentration of metals has exceeded the maximum contaminant level allowed based on the regulation standards in different countries and regions. The use of both a simple visual inspection and a scanner for DGT devices at different deployment times and different temperatures will be considered for this list. Moreover, the rapid screening technique has been evaluated in water and soil from five regions in China. Furthermore, a novel approach with biological material incorporated in the DGT (Bio-DGT) was developed to measure the concentrations and toxicity of metals at the same time in water and soil. The new method immobilised a whole-cell toxicity bioreporter, ADPWH_recA, into a thin layer of agarose gel to replace the polyacrylamide gel that is commonly used in DGT. The test results indicated that the concentrations of metals measured by Bio-DGT and the cell free DGT have no significant differences during a 7-day deployment in synthetic water. A positive metal exposure relationship was shown between Bio-DGT accumulation and biological response. Bio-DGT showed a stable response to heavy metals under a wide range of pH and ionic strength. The bioluminescent signal of Bio-DGT was maintained at a high level during up to 30 days of storage. The deployment of Bio-DGT devices in field soils collected from China allowed the measurement of both the available concentration and the toxicity of metals. It indicated that the new Bio-DGT can assess the bioavailability and toxicity of metals at the same time. The newly developed rapid screening technique for P and metals were applied in waters and soils in situ in 5 different regions of China. It showed the concentrations of P in most of the monitored waters in Beijing were low and the quality of the waters has reached the Chinese water quality standards for surface water. The concentration of DGT-measured P in the two main rivers run through Tianjing were higher than the national water standard in China. The concentrations of Cu in monitored aquatic systems of all field areas have also reached the Chinese water quality standards for surface water.