Water Quality Update Round 2:
Reasons Why Our Test Results Are Different Than ADEM's
Mobile Baykeeper testing from May 29, 2018 indicated much higher levels of bacteria commonly found in sewage (enterococcus) than testing performed by the Alabama Department of Environmental Management (ADEM) and the Alabama Department of Public Health (ADPH) on the same date at the Fairhope Public Beach. We want to help explain what causes these discrepancies.
First and foremost: we have a great deal of respect for the staff members doing testing at ADEM and ADPH and know that the methods they use are valid.
Differences between results likely stem from the fact that ADEM and Mobile Baykeeper use different methods to count enterococci bacteria. ADEM uses the EPA approved Method 1600 (membrane filtration or MF) and Mobile Baykeeper uses the EPA approved Enterolert method. The EPA states that Enterococci are found in the feces of humans and other warm-blooded animals and their presence is an indication of fecal pollution and the likely existence of other pathogens (germs that cause illnesses or diseases) found in human and animal waste.
Studies have shown that while both Enterolert and MF work well, there are a number of important differences between the two tests. A number of studies, including one from the State of Connecticut Department of Public Health, found that Enterolert had a lower chance of finding enterococcus when it is not present (false positive) and that Enterolert was more reliable at finding enterococcus when it is present (thus avoiding false negatives).
Yesterday’s differences may have also been caused by choppy water churning up mud in the Bay. Studies indicate that turbid or muddy water can cause major difficulties mainly by producing false negatives with the MF method that ADEM uses. This issue is not noted with Mobile Baykeeper’s Enterolert method.
Mobile Baykeeper’s number one priority is the safety and health of our members and the community. We will always defer to the more protective test results and therefore at this time we are still advising swimmers to exercise caution at the Fairhope Beach - which includes our racers registered in the Publix Grandman Triathlon this Saturday, June 2. In the event that bacteria levels continue to remain high, the event will be moved to a duathlon (click here to read our duathlon plan). We will make the final call tomorrow on Friday, June 1. For questions or concerns, please contact firstname.lastname@example.org or call 251-433-4229.
For those interested in learning more about the differences between the two methods, the studies below, while not exhaustive, may be of interest:
- Enterolert Limitations - Enterolert limitations can cause false positives where Enterolert detects non-enterococcus bacteria (not fecal indicators).
- Ferguson et al. 2013 - This study assessed whether differences between MF and Enterolert were attributable to the selectivity for certain species within the Enterococcus group.
- Kinzelman et al. 2003 - Study explored: (i) enterococci as an alternative to E. coli, (ii) the impact of the two indicators on regulatory decisions, and (iii) compared MF to Enterolert.
- Abbott et al. 1998 - The 1998 Abbott study states,
“the fact that more…samples were judged acceptable by MF is of concern in view of Enterolert's greater accuracy. If Enterolert had been used to routinely monitor the recreational waters … more samples would have failed…therefore allowing health authorities to respond more rapidly to potentially hazardous public health situations.”
- Eckner 1998 - A total of 338 water samples, 261 drinking water samples and 77 bathing water samples, obtained for routine testing were analyzed in duplicate by Swedish standard methods using, amongst other methods, MF and Enterolert.
- Noble et al. 2003 - Study assessed comparability and within laboratory variability for several methods including MF and Enterolert.
- Noble et al. 2004 - This study compared samples from numerous sites after a major rainstorm using multiple methods including MF and Enterolert.
Abbott, S., Caughley, B., & Scott, G. (1998). Evaluation of Enterolert® for the enumeration of enterococci in the marine environment. New Zealand Journal of Marine and Freshwater Research, 32(4), 505-513.
Budnick, G. E., Howard, R. T., & Mayo, D. R. (1996). Evaluation of Enterolert for enumeration of enterococci in recreational waters. Applied and environmental microbiology, 62(10), 3881-3884.
Eckner, K. F. (1998). Comparison of membrane filtration and multiple-tube fermentation by the Colilert and Enterolert methods for detection of waterborne coliform bacteria, Escherichia coli, and enterococci used in drinking and bathing water quality monitoring in southern Sweden. Applied and Environmental Microbiology, 64(8), 3079-3083.
Ferguson, D. M., Griffith, J. F., McGee, C. D., Weisberg, S. B., & Hagedorn, C. (2013). Comparison of Enterococcus species diversity in marine water and wastewater using Enterolert and EPA Method 1600. Journal of environmental and public health, 2013.
Fricker, C. R., Fricker, E. J., Goodall, T., & Cowburn, J. (1995). Quantitative Procedures for the Detection of E. coli, Coliforms, and Enterococci in Water, Using Quantitray and Enterolert. In Proc. Am. Water Works. Assoc. Water Qual. Technol. Conf, Denver, Colo.
Kinzelman, J., Ng, C., Jackson, E., Gradus, S., & Bagley, R. (2003). Enterococci as indicators of Lake Michigan recreational water quality: comparison of two methodologies and their impacts on public health regulatory events. Applied and Environmental Microbiology, 69(1), 92-96.
Noble, R. T., Weisberg, S. B., Leecaster, M. K., McGee, C. D., Ritter, K., Walker, K. O., & Vainik, P. M. (2003). Comparison of beach bacterial water quality indicator measurement methods. Environmental Monitoring and Assessment, 81(1-3), 301-312.
Noble, R. T., Leecaster, M. K., McGee, C. D., Weisberg, S. B., & Ritter, K. (2004). Comparison of bacterial indicator analysis methods in stormwater-affected coastal waters. Water research, 38(5), 1183-1188.