title: Modification to EPA Method 1623 to address a unique seasonal matrix effect encountered in some U.S. source waters.
abstract: U.S. Environmental Protection Agency (EPA) Method 1623 is designed to detect and determine concentrations of Cryptosporidium oocysts and Giardia cysts in water through concentration, immuno-magnetic separation (IMS), and immuno-fluorescence assay with microscopic examination. A seasonal interference with the method was observed in some municipal source waters collected from reservoirs and as reported to Shaw Environmental, Inc. in the summers of 2005, 2006, and 2007. This interference, which was not confined to a single region of the nation, caused clumping of the IMS beads during the acid dissociation of the IMS procedure in Method 1623. This effect lowered method recoveries for both Cryptosporidium and Giardia; however, the effect was more pronounced for Giardia. A heat dissociation technique (Ware et al., (2003) J. Microbiol. Methods 55, 575-583) was shown to be a viable option for samples which demonstrate the clumping matrix effect and improved Giardia recoveries in partially clumped samples. The heat dissociation application holds promise for fully clumped samples and warrants further investigation.
authors.affiliation: Shaw Environmental Inc., 26 W. Martin Luther King Dr., Cincinnati, OH 45219, USA. shaw.nancy@epa.gov
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Shaw
authors.forename: Leah Fohl
authors.initials: LF
authors.lastname: Villegas
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Eldred
authors.forename: Deborah H
authors.initials: DH
authors.lastname: Gaynor
authors.forename: Paul S
authors.initials: PS
authors.lastname: Warden
authors.forename: Barry V
authors.initials: BV
authors.lastname: Pepich
mesh_terms: D000818:Animals; D003458:Cryptosporidium / Q000302:isolation & purification*; D005872:Giardia / Q000302:isolation & purification*; D018189:Immunomagnetic Separation / Q000379:methods*; D008856:Microscopy, Fluorescence; D014481:United States; D014484:United States Environmental Protection Agency; D014867:Water / Q000469:parasitology*; D014881:Water Supply / Q000032:analysis
chemical_list: D014867:Water