The Analytical Methods Of Trace Level Methylmercury In Environmental Samples In Southern Tibetan Plateau

The concentrations of methylmercury in natural waters are extremely low and at "trace levels". Thus,quantification of methylmercury is very difficult and urges stringent protocols for sample bottles, storage environment, sensitivity and stability of experimental instrument. Accordingly, appropriate reagent containers should be used to minimize potential contamination during the sampling and storage of methylmercury. In this study, a series of experiment of basic device condition and quality control were conducted. These experiments include determination of method detection limit and standard curve and quality control such as recovery, testing stability of instrument by repeatable measurements of standard samples with gradient concentrations over times. We selected a batch of reagent bottles made of six different materials, i.e., Polypropylene (PP), High density polyethylene (HDPE), Low density polyethylene (LDPE), Borosilicate glass (GLASS), Polycarbonate (PC) and Polyfluoroalkoxy (PFA), to perform a series of tests to assess their blank values. The tests include 5-hour and 5-day leaching blank tests, and upstanding, horizontal and inverted storage tests. Results indicated negligible blanks in the PP, PC and PFA reagent bottles. The Corning PP centrifuge tube can be used for methylmercury sampling and storage without rinse considering its portability and relatively low cost. Samples of three representative environmental compartments, including water, fish and soil, on the Tibetan Plateau were collected and measured for methylmercury using the established detection method. The results and analysis indicated the following conlusion.1.the method detection limit of the device is 0.002 ng/L and the standard curve equation of low concentration is: y=4293x-7.398(the value for blank sample is 0.001 ng/L, R2=0.999) and the standard curve equation of high concentration is y=3048.37 x +29.17 (the value for blank sample is 0.001 ng/L, R2=0.9999). The stability of the device is within the specific range in testing of samples with low concentration and high concentration, concentration gradient of continuous or discontinuous days, suggestive of accurate detection of methylmercury in in samples with a wide range of methylmercury concentrations using the instrument.2. The blank values of brand-new reagent bottles made of PP, PC, PFA are negligible. In consideration of economic factor and portability, Corning PP centrifuge tube is recommended for field sampling without pre-rinse in laboratory.3. Storage test for 2,3,7,15,21,30 and 60 days suggested that measurement of methylmercury is reliable and repeatable in samples stored appropriately up to at least 60 days.4. Measurement of methylmercury in typical environmental samples from the Tibetan Plateau approved that the detecting method developed in this study is reliable and can be potentially applicable universally for samples from the Tibetan Plateau and other remote regions.