In-situ tryptophan-like fluorescence: A real-time indicator of faecal contamination in drinking water supplies

Abstract

Enteric pathogens are typically inferred from the presence of surrogate indicator organisms such as thermotolerant (faecal) coliforms (TTCs). The analysis of TTCs requires time-consuming incubation in suitable laboratories, which can limit sampling resolution, particularly during critical pollution events. Here, we demonstrate the use of in-situ fluorimeters targeting tryptophan-like compounds as a rapid, reagentless indicator of TTCs in groundwater-derived potable water supplies in Africa. A range of other common indicators of TTCs were also determined including nitrate, turbidity, and sanitary risk survey scores. Sampling was conducted during both the dry and wet seasons to investigate seasonality. Tryptophan-like fluorescence was the most effective predictor of both presence/absence and number of TTCs during both seasons. Seasonal changes in tryptophan-like fluorescence in deeper supplies suggest it is transported more efficiently through the aquifer than TTCs. Moreover, the perennial elevated concentrations in some wells suggest it is more resilient than TTCs in groundwater. Therefore tryptophan-like fluorescence could also be a better indicator of some smaller, more easily transported, and long-lived, pathogenic enteric viruses. These sensors have the potential to be included in real-time pollution alert systems for drinking water supplies throughout the world, as well as for mapping enteric pathogen risks in developing regions.

Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health

“…Studies by Howard et al (2003) and Sorensen et al (2015a, b) are two notable examples where detailed seasonal monitoring of microbiological indicators was carried out over a 12 month period to characterise the risk factors for spring contamination in Kampala, Uganda, and shallow wells and boreholes in Kabwe, Zambia. Significantly higher contamination has been observed after rainfall events and there was strong evidence that rapid recharge of the shallow groundwater causes a rapid response in spring and shallow well water quality (Barrett et al 1998;Sorensen et al 2015b). …”

“…Open and unlined wells are consistently of poorer quality compared to lined or 'improved' wells (e.g. Godfrey et al 2006;Sorensen et al 2015b). Boreholes generally have the best water quality, however in some studies springs have been found to be of better quality compared to boreholes (e.g.…”

“…While clearly less important from a health perspective compared to microbiological contamination, chemical contaminants also pose a threat to water quality, and they are very Borehole < well Sorensen et al (2015b) FC faecal coliforms; FS faecal strep. ; EnC enterococci, TC total coliforms, BDL below detection limit useful tracers of microbiological contaminants, which are inherently more transient in groundwater systems.…”

“…Mattioli et al 2012;Sorensen et al 2015a) for fingerprinting pathogens as well as new fluorescence sensor technology for rapidly mapping microbiological contamination of water sources (e.g. Sorensen et al 2015b) and other field tests may offer new ways to discriminate between different pathogen sources and pathways for contamination and rapidly assess potential health risks associated with vulnerable groundwater sources.…”

Tracing enteric pathogen contamination in sub-Saharan African groundwater

“…TLF is a proteinaceous component of the fluorescent dissolved organic carbon spectrum and a well-established indicator of wastewater and biological oxygen demand (Baker 2001;Cohen et al 2014;Henderson et al 2009;Lapworth et al 2008;Stedmon et al 2011). Recently, it has been demonstrated as a precautionary real-time, reagentless indicator of TTCs in freshwater in Africa (Baker et al 2015;Sorensen et al 2015a). However, its effectiveness at inferring waterborne pathogen presence is unknown.…”