MICROBIOLOGICAL SOURCE TRACKING: WHERE ARE WE NOW AND WHERE ARE WE GOING?

Microbial Source Tracking (MST) methods are being applied on an increasing basis to fecal source contamination to assist in solving water quality issues in watersheds. Many of these methods are still in development and most have not been extensively tested in watersheds. A recent workshop sponsored by Southern California Coastal Water Research Project (SCCWRP), U.S. Environmental Protection Agency (EPA), National Water Research Institute (NWRI), and California State Water Resources Control Board (CSWRCB) attempted to define the current status of this technology and to map the logical direction for evaluation and comparison of methods available for future applications. The MST methods considered during the workshop were categorized by either phenotypic or genotypic characteristics and whether or not they required a database collection. Several research issues were identified as critical, irrespective of individual technique, for example, temporal, spatial, and matrix effects, fingerprint database size, practicality vs. statistical design, and lack of uniform standards or reference materials. Factors which also must be considered for evaluation of MST methods prior to selection for use in a watershed were: accuracy, sensitivity and specificity, ease of use, cost, equipment, and database vs. non-database methods. Of major concern was the area of statistical issues which included: sampling design, replication, sample size, inter-laboratory comparisons, lack of accepted standards for comparisons, power analysis and sources of variance. A tiered approach was suggested for setting standards criteria for evaluation of methods and their effectiveness in identifying sources of fecal contamination. Tier 1 (Measurement Criteria) would address reproducibility and resolution; geographical, temporal, and matrix stability; and evaluation of data by peer review. Tier 2 (Perception Criteria) would include relationships to source; water quality indicators; public health outcomes; and ease of technology transfer. Tier 3 (Cost Criteria) would encompass equipment; training; implementation time; and legally defensible cost inflation. Tiered inter-laboratory research approaches were also recommended such as: lab validations (isolates vs. fecal vs. water; single vs. multiple protocols); database building (inclusion of human, pet, livestock and wildlife isolates); testing predictive capabilities of methods; and field trials in dominant source watersheds. Much work remains to be done in the evaluation of MST methodologies before they can be applied in a universally accepted manner to watersheds. However, a preliminary roadmap has been discussed which may provide directions for the “off road” areas that need to be addressed before the trip can continue.