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VALIDATION OF EPA METHOD 1682: SALMONELLA IN BIOSOLIDS BY MODIFIED, SEMISOLID RAPPAPORT-VASSILIADIS (MSRV) MEDIUM
Citation:
Pope, M., Y. Chambers, AND M C. Meckes*. VALIDATION OF EPA METHOD 1682: SALMONELLA IN BIOSOLIDS BY MODIFIED, SEMISOLID RAPPAPORT-VASSILIADIS (MSRV) MEDIUM. Presented at American Society for Microbiology Annual Meeting, New Orleans, LA, May 23 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
Treated biosolids may be applied to land as a crop nutrient and soil conditioner. However, land application of biosolids may pose the risk of releasing pathogens into the environment if disinfection and use criteria established by EPA at 40 CFR part 503 are not met. Among these criteria are limits for Salmonella, which are pathogenic bacteria that can cause salmonellosis in animals and humans. EPA and the CSC Biology Studies Group conducted a study to characterize in multiple laboratories the precision and recovery of a new EPA method for Salmonella in biosolid matrices. Methods: EPA Method 1682 requires enrichment, followed by selection using MSRV medium and biochemical/serological confirmation. Twelve volunteer laboratories participated in the validation of Method 1682 in 2003. During the study, the following biosolid matrices were evaluated: alkaline-stabilized, compost, Milorganite® (a commercially available heat-dried biosolid), and thermophilically digested. For each matrix, every laboratory analyzed one unspiked sample, 2 to 4 samples spiked with precisely enumerated BioBalls™ of Salmonella typhimurium (ATCC# 14028), and 2 to 4 samples spiked with laboratory-prepared Salmonella typhimurium (ATCC# 14028) spiking suspensions. Results: Based on preliminary assessments, overall mean recoveries from samples spiked with BioBalls™ were 19%, 42%, 80%, and 52% for alkaline-stabilized, compost, Milorganite®, and thermophilic samples, respectively; with standard deviations of 28%, 40%, 59%, and 57% for the same matrices. Overall mean recoveries for samples spiked with laboratory-prepared spiking suspensions were 55%, 101%, 123%, and 48% for alkaline-stabilized, compost, Milorganite®, and thermophilic samples, respectively; with standard deviations of 43%, 93%, 101%, and 57% for the same matrices. Preliminary results indicate that, while recoveries for Method 1682 appear to be acceptable for the matrices evaluated, sample results can be quite variable. Based on the results of this study, it is recommended that multiple samples be evaluated to assess biosolid quality prior to land-application.