Chapter 23
Studies on the Applications of an Immunoassay for Mercury 1
2
1
Larry C. Waters , Richard W. Counts , Rob R. Smith , and Roger A. Jenkins Downloaded by STANFORD UNIV GREEN LIBR on October 6, 2012 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1997-0657.ch023
1
1
2
Divisions of Chemical and Analytical Sciences and Computer Sciences and Mathematics, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6120
Immunoassays (IAs) are rapidly becoming a significant component of the arsenal of field analytical methods. Validation of such alternative methods is necessary for their acceptance by the regulatory agencies and potential users. As part of a program to evaluate the performance of such methods, the capacity of the BiMelyze (BioNebraska, Inc.) immunoassay-based method to measure mercury in soil and sludge was examined. Results showed that the immunoassay method performed as well as either X-ray fluorescence or neutron activation methods for the analysis of mercury in contaminated soil samples. The method was also shown to be capable of detecting as little as 2.5 ppm mercury in sludge from a waste water treatment plant.
Sample analysis is a major component of environmental restoration and waste management activities. Standard laboratory methods are both expensive and timeconsuming. A major portion of the field samples taken to the laboratory for analysis either are negative for the analyte being tested, or are contaminated below the regulated level. Effective field analytical methods could eliminate much of this effort and expense. An objective of this program is to define commercial screening methods that are capable of measuring environmental contaminants of concern to the Department of Energy (DOE) (7,2). The approach involves selecting potentially useful technologies, experimentally evaluating the methods that utilize the technology, and transferring the validated methodology to appropriate users. Of specific concern to the DOE at its facilities at Oak Ridge, TN, is the mercury that is contaminating the flood plain of the East Fork Poplar Creek. Arising from releases in the 1950s by an upstream nuclear weapons plant, it has been estimated that as much as 80,000 kg of mercury still remain in the flood plain soils (J). An account of our experiences with an immunoassay-based method for the analysis of mercury in those soils, and in sludge generated at the city of Oak Ridge waste water treatment facility, will be presented.
© 1997 American Chemical Society In Immunochemical Technology for Environmental Applications; Aga, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
23.
WATERS E T A L .
281
An Immunoassay for Mercury
Description of the Mercury Immunoassay Method The kits used in our evaluation studies are the BiMelyze 96-Well Plate Mercury Assay Kit and the BiMelyze 16-Tube Mercury Assay Kit, with associated extraction kits. They were obtained from BioNebraska, Inc., Lincoln, NE. The basis for these kits is a monoclonal antibody to Hg , produced and described by Wylie, et al (4,5). Materials required but not supplied in the 96-well plate kit include the pipets required for making sample dilutions and adding samples and reagents to the plates, and a plate reader. Because the tube kit utilizes dropper-topped bottles to deliver samples and reagents, there is no requirement for pipettors. Tubes are read with a differential photometer. Both kits require a user supplied balance to weigh the samples, and the nitric and hydrochloric acids used to extract the soil. Easy to follow instructions are provided with the kits. The plate format is well suited for the analysis of multiple samples in the laboratory while the tube format is more appropriate for onsite field use.
Downloaded by STANFORD UNIV GREEN LIBR on October 6, 2012 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1997-0657.ch023
2+
Preparation of Samples for Analysis. A 1-g sample of soil is shaken intermittently with 3 mL of a 2:1 mixture of concentrated HC1 and concentrated H N 0 for 10 min. This procedure converts poorly soluble salts of mercury, e.g., HgS, elemental mercury, and to some extent methyl mercury, to soluble forms of H g . The extract is partially neutralized by the addition of 7 mL of buffer, effecting a 1 to 10 dilution of the sample. (Caution: protective apparel should be worn and care taken during these extraction steps.) A further 1 to 1000 dilution is made (total dilution equals 1 to 10,000) before the extract is analyzed. Consequently, a 5-ppm sample is equivalent to 0.5 ppb in the assay. Water, in the absence of interferences, can be analyzed directly with a sensitivity of
