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Derivation of the equivalent qPCR value for Escherichia coli to existing culture-based water quality standards for monitoring beaches in Michigan
Citation:
Briggs, S., M. Sivaganesan, O. Shanks, R. Haugland, S. Siefring, M. Varma, K. Oshima, A. Dufour, S. Nappier, AND B. Schnitker. Derivation of the equivalent qPCR value for Escherichia coli to existing culture-based water quality standards for monitoring beaches in Michigan. IWA 20th International Symposium on Health Related Water Microbiology, Vienna, AUSTRIA, September 15 - 20, 2019.
Impact/Purpose:
Inform international public health officials and scientists on the current status of EPA efforts to support implementation of rapid recreational beach monitoring by quantitative PCR methods in Michigan.
Description:
A quantitative polymerase chain reaction (qPCR) method (Draft Method C) has been developed for Escherichia coli (E. coli) by the United States Environmental Protection Agency (USEPA). However, a beach notification threshold value is needed for this method and has not been determined. To implement Draft Method C for monitoring beaches in Michigan, the Department of Environmental Quality (DEQ) led a 3-year effort with fourteen labs to share 6,669 water samples from 108 beaches with the USEPA National Exposure Research Laboratory (NERL). Selected beaches were representative of both the upper and lower peninsulas of Michigan with urban and rural locations on inland lakes and the Great Lakes. Samples were analyzed by local labs using a state and USEPA-approved culture method (Colilert) and by both NERL and the local labs using Draft Method C. Linear relationships between culture and Draft Method C results were determined. Final analysis was based on results from a combined total of 2,092 samples from 39 beaches with at least one exceedance of the Michigan water quality standard by culture, at least 10 paired samples with quantitative estimates for both methods, and a minimum R2 of 0.6 between the methods per beach. From this analysis, a Draft Method C qPCR value of 1.863 log10 copies per reaction was determined to be equivalent to the Michigan culture standard of 300 E. coli per 100 milliliters (ml). The new beach notification value for Draft Method C will be implemented for monitoring Michigan beaches and will improve the protection of public health by providing results in hours instead of the next day.