Transport of chemical and microbial compounds from known wastewater discharges: potential for use as indicators of human fecal contamination

Glassmeyer, S.T., Furlong, E.T., Kolpin, D.W., Cahill, J.D., Zaugg, S.D., Werner, S.L., Meyer, M.T. and Kryak, D.D. (2005) Environmental Science & Technology, 39 (14); 5157-69.

In order to protect public health, the quality of drinking and recreational water is monitored to ensure pathogens are not present. Indicator organisms are monitored in water supplies because of the large number of potential pathogens that may be present. Direct analysis is often impractical as some pathogenic organisms cannot be cultured. Indicator species should be present when pathogens are present and in sufficient concentrations to make them easy to detect. Indicators are selected that are more environmentally stable and are more resistant to disinfectants than the pathogens they trace so they are easy to detect and identify.

In the U.S. currently, the total coliform test is used for screening drinking water samples for potential pathogen contamination. Recreational waters are now screened in the U.S. by monitoring E. coli and enterococci. These indicator bacteria have been useful in protecting human health but they also have their limitations and disadvantages. The traditional biological assays require 18-48 hours for microorganisms to grow and to be enumerated. In the time it takes for a result to be obtained, individuals can consume or come in contact with the contaminated water. Many microbial indictors lack specificity and it is not possible to discriminate between human or animal sources or to even establish whether the presence of indicators is a result of faecal contamination.

The applicability of using chemical indictors of human faecal contamination to identify human sewage contamination in water is a relatively new area of research. The advantage of chemical tests over current microbial tests is the shorter time required for sample preparation and analysis. Also, chemical indicators offer the potential of being able to distinguish between human and animal sources. This study was conducted to evaluate the usefulness of a range of organic chemical compounds as specific indications of human faecal contamination.

Ten wastewater treatment plants across the United States were studied. One upstream, one effluent and two downstream water samples from each WWTP were collected. Two remote sites were also sampled (reference locations), these having minimal direct impact from human wastewater. The persistence of a chemically diverse range of emerging contaminants in streams was determined. There were 110 chemical analytes investigated in this study. Of these, 78 were found in at least one sample. The number of compounds found per sample ranged from three in a reference location to 50 in a WWTP effluent sample. The total analyte load varied from 0.018 microg/L at a reference location to 97.7 microg/L in a WWTP effluent sample. Most of the compound concentrations were in the range of 0.01 -1.0 micro g/L, however in some samples individual concentrations were in the range of 5-38 micro g/L.

The two microbial indicators E. coli and enterococci were found in more than 90% of the samples. In contrast to the chemical analytes, E. coli and enterococci were found in both collected reference samples. This shows the lack of specificity of the microbial indicators for identifying only human faecal contamination.

The results suggest that chemicals may be useful as indicators of human faecal contamination. For the majority of the chemicals present in the samples, concentrations generally followed the expected trend where they were either nonexistent or at trace levels in the upstream samples and in maximum concentrations in the WWTP effluent samples with a decline by the downstream samples. There were 35 chemicals in particular that could be useful indicators. The wastewater compounds ethyl citrate, galaxolide and tonalide go through distinct changes in concentrations between upstream, WWTP effluent and downstream sites and this could make them good indicator candidates. Compounds that are only used by humans such as the pharmaceuticals carbamazepine and diphenhydramine and even caffeine may also be potentially good indicators. Of the faecal sterols, coprostanol which has a human source showed the most changes in concentrations between the sample sites and had the greatest potential as an indicator of human faecal material. No compounds should be ruled in or out until an epidemiological study has compared its presence or concentration to the incidence of illness such as gastroenteritis caused by water contact.