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IDENTIFICATION OF SOURCES OF FECAL POLLUTION IN ENVIRONMENTAL WATERS
Citation:
SANTO-DOMINGO, J., S. GLASSMEYER, O. C. SHANKS, C. A. KELTY, Y. OLIVAS, R. A. HAUGLAND, M. MOLINA, J. PAAR, R. B. LANDY, B. R. JOHNSON, AND B. SMITH. IDENTIFICATION OF SOURCES OF FECAL POLLUTION IN ENVIRONMENTAL WATERS. Presented at BOSC review on WQ, Cincinnati, OH, January 25 - 27, 2006.
Impact/Purpose:
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Description:
A number of Microbial Source Tracking (MST) methods are currently used to determine the origin of fecal pollution impacting environmental waters. MST is based on the assumption that given the appropriate method and indicator organism, the source of fecal microbial pollution can be identified. However, the accuracy of several MST approaches in field study situations has been questioned due to a number of problems associated with the target organisms, the level of complexity introduced by spatial and temporal vectors, the stability of the markers used, and poor sampling protocols. A research program was initiated to develop and evaluate several MST methods. In addition, a series of regional workshops and government and academic researcher meetings were organized by EPA-regional and ORD personnel to assist stakeholders understand the assumptions and limitations of MST and to develop an MST guide document. Ongoing efforts have focused on performing 16S rDNA sequence analyses to search for alternative bacterial source tracking targets. Thus far, we have generated several fecal clone libraries (i.e., from cattle, horse, pig, goat, and sheep) for Bacteroides spp. The results from these studies indicate that a considerable number of novel sequences are associated with these fecal samples. Phylogenetic analysis from these environmental clone libraries showed well-defined clusters. We are currently expanding these studies to include other fecal anaerobic bacterial groups. Bacteroides host-specific primers were also used to validate the specificity of host-specific PCR assays. Although these results suggest that some Bacteroides populations are preferentially distributed in different gut systems, the cross amplification with nonspecific hosts implies that 16S rDNA might not be as good of a target for the development of host specific assays as suggested in early studies. Future studies will focus in the evaluation of spatial and temporal stability of currently available markers in fecally contaminated waters and in the use of metagenomics to develop novel molecular markers based on host-microbial interactions. The utility of the latter markers will be evaluated as part of an ongoing epidemiological study. To complement the microbial-based work, research has also begun to examine the potential of using human household chemicals from many different classes-including pharmaceuticals, surfactants, and fecal sterols- as tracers of human fecal contamination. Initially, these collaborative projects with the U.S. Geological Survey focused on the presence of these compounds in municipal wastewater effluents, and their persistence away from the source. The occurrence of these chemicals was further explored in subsequent studies, in which the time of travel was incorporated into the sample design. This is necessary in order to better understand the difference in the environmental persistence kinetics of these compounds. These studies determined that some compounds are too ubiquitous to be useful as indicators while the varying persistence of the other compounds show statistically significant different decreases. These differences in persistence may be useful in determining the distance to the source of the fecal pollution. In addition, these data are being evaluated as part of ongoing epidemiological studies to determine which chemical compounds are associated with health risks and thus have most potential of being used as indicators of human fecal pollution.