Sonji Romero, left, and Zaira Valdez from the City of San Diego’s marine microbiology lab practice using a quantitative PCR machine to test water samples for microbial contamination during a SCCWRP-led training and intercalibration exercise in 2013.
EPA’s Pacific Southwest Region announced approval of an innovative, quick turn-around DNA-based method to evaluate bacteria in San Diego County beach water. The San Diego County rapid test is the first demonstration of the use of this method for routine beach monitoring in the world.
This method was developed for beach use by the Southern California Coastal Water Research Project and implemented in collaboration with the California Department of Public Health (CDPH). By using this digital test to measure bacterial DNA in beach water, San Diego County beach managers will be able to provide same-day notices of beach water quality.
“We applaud San Diego County for further advancing the science in beach monitoring by piloting this innovative rapid test method,” said EPA Pacific Southwest Water Division Director Tomás Torres. “Same-day beach water quality results will facilitate more effective beach management decisions to ensure that beachgoers are protected moving forward.”
“The collaborative study between CDPH and the County of San Diego demonstrated ddPCR to be a reliable method for monitoring beach water quality conditions,” said Dr. Mark Starr, Deputy Director for Environmental Health, CDPH. “Combined with same-day results, ddPCR will be a great tool for expediting notifications of both poor water quality conditions and the return to safe conditions to recreational beach users.”
“San Diego County will be the first coastal community in the country to provide beach users with same-day water quality results when this new rapid test is implemented later this year,” stated San Diego County Board of Supervisors Vice Chair Nora Vargas. “This was truly a great collaboration of private, local, state and federal agencies that will help protect the health of our residents and visitors to San Diego County beaches.”
Southern California Coastal Water Research Project’s Meredith Raith conducting water-quality sampling at an Orange County beach in 2016. (photo by SCCWRP)
Harmful levels of bacteria in beach water typically last less than one day in California, but current beach water bacterial sampling methods require 18-24 hours to produce results. The delay between sample collection and public notification of results may leave beachgoers unknowingly exposed to harmful bacteria and slows the removal of signage restrictions when risks have abated. The digital droplet polymerase chain reaction (ddPCR) method not only significantly shortens the turnaround time between sampling and results to less than four hours on average but is also able to detect lower levels of bacterial exceedances than current testing methods.
While developing the environmental application of the ddPCR beach water testing method, San Diego County environmental health officials, alongside the California Department of Public Health, the Southern California Coastal Water Research Project, and the University of California, San Diego embarked on a two-year-long study comparing bacterial concentration measured with ddPCR to measurements gathered by existing methods. The study took samples across 70 miles of county coastline. The recently published results found good agreement between the methods.
Final approval of using ddPCR for regular beach monitoring will be determined by the success of this pilot program, with input from the California Department of Public Health and California’s Environmental Laboratory Accreditation Program.
For more information on beach water quality, please visit https://www.epa.gov/beaches.
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