Research On The Current Status Of The Contamination Of Heavy Metals In Tonghui River System Of Beijing

The aim of effective control of heavy metal pollution of water to improve thequality of water and guarantee the safety of water source areas is one of the majorobjectives and tasks for the12th Five-Year National Plan for EnvironmentalProtection. It is also an important content of constructions of Green Beijing and worldcity with Chinese characteristics Beijing. Heavy metals are known to damage humanhealth due to their characteristics including heavy toxicity, being difficult to bemetabolized and being easy to be bioaccumulated. In recent years, heavy metalcontamination has become one of the main problems of water pollution. However,most of the heavy metals exist in water with trace or ultra trace amounts. Hence, theestablishment of analytical methods for heavy metals with large enrichment factor,high sensitivity and accuracy and easy operation not only lays a foundation for theevaluation and prevention of environmental pollution, but also provides considerablereferences for environmental protection and sustainable development.This work was aimed at the determination of the concentration of heavy metals inTonghui river system, which is the principal river in Beijing city. Three enrichmentmethods were compared and the cloud point extraction （CPE） was selected as theoptimal enrichment method. Quantitative analysis were carried out for thedetermination of lead, cadmium, copper and nickel in Tonghui river system using highresolution continuum source graphite furnace atomic absorption spectrometry （HR-CSGFAAS）. The distribution trends of the four heavy metals were explored. Firstly, thecomparison of the three enrichment methods, including coprecipitation, ion exchangeand CPE, was performed to find out the most effective enrichment method for lead inwater samples. The results indicated that CPE was the optimal enrichment method dueto its less consumption of water samples, larger enrichment factor and simplerprocedure compared with the other two methods. Secondly, trace amounts of lead,cadmium, copper and nickel were extracted from water samples by CPE with1-（2-pyridylazo）-2-naphthol （PAN） as chelating agent and Triton X-114as non-ionicsurfactant. The optimal conditions of the methods were established. Finally, theconcentration of lead, cadmium, copper and nickel in the water samples from Tonghuiriver system were detected using HR-CS GFAAS combined with CPE.The results indicated that The limits of detection （LOD） for lead, cadmium, copper and nickel were0.080μg L^-1,0.0095μg L^-1,0.035μg L-1and0.014μg L^-1,respectively. The sensitivities of the methods improved2to3orders of magnitudecompared with that of the national standard methods. The method was employed forthe repeatability experiments and determination of lead, cadmium, copper and nickelin the standard samples of natural water. The results indicated that the determinedvalues were consistent with the standard values, which demonstrated that the methodhad high accuracy for the detection of heavy metals in environmental water samples.The contents of lead, cadmium, copper and nickel in fifty-five water samples fromTonghui river system were0.10³.4μg L^-1,0.012⁰.20μg L^-1,0.98³.7μg L^-1,0.38⁷.7μg L^-1, respectively, which were all conformed to the EnvironmentalQuality Standards for Surface Water （Grade I）, and their distribution trends wererelated with the surrounding environments.This work provides abundant experimental data of heavy metals contents ingroundwater in Beijing city, the enrichment and analytical methods employed in thiswork provide not only reliable quantitative methodology for the determination oftrance-amount heavy metals in water, but also important references for theconstruction of related standards and regulations about water quality. The results ofthis investigation will lay a foundation for evaluating the quality of surface water inBeijing city and for establishing and implementing the comprehensive renovationplanning for surface water basin. Meanwhile, it has considerable significance forstrengthening national consciousness of water environmental protection and forpromoting the sustainable development of Beijing.