Validation of a Novel Bioassay for Low-level Perchlorate Determination

Abstract : The bioassay for low-level perchlorate determination (range approximately 6 to 40 g/L), which was the focus of the project, is a benchtop enzyme assay combined with a perchlorate concentration and purification step using solid phase extraction (SPE) cartridges (Heinnickel et al., 2011). It is based on perchlorate reductase activity and couples NADH oxidation to perchlorate reduction, with PMS as an electron shuttle. Hence the amount of perchlorate in an aqueous sample can be determined enzymatically by monitoring the amount of NADH oxidized spectrophotometrically (i.e. by measuring the decrease in absorbance at 340 nm). The instrumentation for the bioassay is a UV spectrophotometer. The equipment and materials are relatively inexpensive and the bioassay potentially may be performed by less highly trained personnel than required by IC or LC/MS analytical methods. Thus the benchtop bioassay might supplement more expensive and time consuming analytical methods as a screening test for perchlorate in groundwater to facilitate tasks such as mapping plumes and monitoring perchlorate levels during remediation. The goal of the project was to determine whether results with the benchtop bioassay were in agreement with those of a reference analytical method using diverse groundwater sources. If results with the benchtop bioassay performed in the PI s laboratory were comparable to reference analytical methods, it was planned to develop and test a kit format of the bioassay that could be used in the field. The enzymatic bioassay for perchlorate was developed under SERDP Project ER 153019. Bioassay results with groundwater collected from three different locations at one site were in good agreement with results obtained by a reference IC method. The levels of perchlorate in these samples were approximately 10, 22, and 71 g/L. This testing was performed in a 96 well microplate using a microplate reader inside of an anaerobic chamber with an atmosphere of nitrogen and hydrogen.