Soil: the environmental source of Escherichia coli and Enterococci in Guam's streams

Abstract

We have previously documented that faecal indicator bacteria (Escherichia coli, faecal coliform, enterococci) recommended by the U.S. Environmental Protection Agency (USEPA) to establish recreational water quality standards are naturally found in high concentrations in the surface and subsurface of soils in Hawaii. Rain, the source of all streams in Hawaii, washes the soil sources of faecal bacteria into all the streams of Hawaii, at concentrations which consistently exceed the USEPA recreational water quality standards. The objective of this study was to test the hypothesis that faecal bacteria are able to establish themselves in the soil environments of tropical islands by conducting the same study in Guam, a tropical pacific island with warmer temperatures and higher humidity than Hawaii. The same methods and study design used in Hawaii was used in Guam. The results of the study conducted in Guam revealed that all streams contain consistently high concentrations of faecal coliform, E. coli, and enterocci which exceeded the old USEPA recreational water quality standard of 200 faecal coliform/100 ml as well as the new water quality standards of 126 E. coli/100 ml or 33 enterococci/100 ml. These same faecal indicator bacteria were recovered in high concentrations in surface and subsurface (18-36 cm depth) soil samples in Guam. Limited coastal water analysis showed that most coastal marine waters contain low concentrations of faecal bacteria but coastal waters impacted by stream run-off showed elevated levels of faecal bacteria. The results of this study support the hypothesis that environmental conditions in the tropical areas of the world can support the growth and establishment of populations of faecal bacteria in the soil. Thus, soil becomes an environmental, non-faecal source of faecal indicator bacteria. These results indicate that USEPA water quality standards may not be directly applicable to tropical island environments.

Influences of natural and anthropogenic factors on surface and groundwater quality in rural and urban areas

“…An adequate faecal indicator does not reproduce outside the animal host. E. coli and enterococci grow, survive and establish their populations in natural environments such as freshwater lakes and streams (Byappanahalli et al 2003;Power et al 2005), algal wrack (Olapade et al 2006;Whitman and Nevers 2003), beach sand (Byappanahalli, Whitman, Shively, Ting, et al 2006;Whitman et al 2005), soils and sediments (Anderson et al 2005;Byappanahalli and Fujioka 2004;Byappanahalli, Whitman, Shively, Sadowsky, et al 2006;Fujioka et al 1999;Ishii et al 2006;Solo-Gabriele et al 2000;Whitman et al 2005), and plant cavities (Whitman et al 2005).…”

Quantitative evaluation of bacteria released by bathers in a marine water

“…Studies conducted in Hawaii and Guam (Fujioka, 1988;Fujioka and Roll, 1997;Fujioka et al, 1999), and in Puerto Rico (Toranzos and Marcos, 2000) have shown that in the absence of any known sources of human/animal waste, enterococci and E. coli are consistently present and recovered in high concentrations in the subtropical environment. Specifically in South Florida, river bank soils and beach sands have been implicated as the source of indicator microbes to the water column (Desmarais et al, 2002;Rogerson et al, 2003;Shibata et al, 2004).…”

Relating Watershed Characteristics to Elevated Stream Escherichia coli Levels in Agriculturally Dominated Landscapes: An Iowa Case Study

“…In many watersheds, wildlife such as geese and deer are a significant source of E. coli [5][6][7]. E. coli is also associated with point-source discharges of human wastes such as those which occur at wastewater treatment plants [8]. The concentration of fecal coliforms in treatment plant effluent depends on flow, treatment type, and the target bacterial population [9,10].…”