Survival of Fecal Indicator Bacteria on Pervious Environmental Surfaces

Abstract

Because of difficulties in the measurement of sewage-borne pathogens, the microbiological quality of water is typically characterized and regulated on the basis of indicator species. These organisms are assumed to derive from a common source with pathogens of interest, and to arrive in, survive in, and move through watershed environments in numbers that sufficiently correlate to those pathogens to provide meaningful information concerning health risks. Commonly used fecal indicator bacteria (FIBs, notably E. coli, and Enterococcus spp.), however, may derive from sources other than sewage, and survive in the (non-enteric) environment at rates divergent from those of the pathogens they are presumed to indicate. Reliance on the use of FIBs to manage microbiological risk of environmental waters would be better informed by knowledge of the non-sewage contributions of FIBs to stormwater runoff. In an ongoing effort to model background (i.e. of nonhuman origin) discharges of indicator species from stormwater source areas, results of a (2 5 ) study into environmental factors relevant to survival (modeled as a log-linear segmented relationship with unknown breakpoints) of E. coli and Enterococci on pervious (soil) surfaces over extended time is presented. BACKGROUND Field and Samadpour (2007) provide a critical review of both the “indicator paradigm” (our current reliance on fecal indicator bacteria, FIBs) and an alternative monitoring regimen utilizing fecal source tracking (FST) methods as frameworks for determining and monitoring the biological quality of surface waters and the risks they present. While noting the inadequate state of the art for direct measurements of pathogens, the authors find deficiencies in the correlations of FIBs to specific pathogens, and of FIBs to epidemiological measures of human health. They ascribe the deficiencies in the indicator paradigm to its inability to identify the source hosts of environmental FIBs. Landscape survival of FIBs and the ratio of FIBs to human pathogens deposited on the landscape are dependent on the source of the feces. More specifically, though zoonotic infections from non-human sources occur, correlation between human health threat and FIB presence suffers when major fecal sources