Abstract
We explore in-situ fluorescence spectroscopy as an instantaneous indicator of total bacterial abundance and faecal contamination in drinking water. Eighty-four samples were collected outside of the recharge season from groundwater-derived water sources in Dakar, Senegal. Samples were analysed for tryptophan-like (TLF) and humic-like (HLF) fluorescence in-situ, total bacterial cells by flow cytometry, and potential indicators of faecal contamination such as thermotolerant coliforms (TTCs), nitrate, and in a subset of 22 samples, dissolved organic carbon (DOC). Significant single-predictor linear regression models demonstrated that total bacterial cells were the most effective predictor of TLF, followed by on-site sanitation density; TTCs were not a significant predictor. An optimum multiple-predictor model of TLF incorporated total bacterial cells, nitrate, nitrite, on-site sanitation density, and sulphate (r2 0.68). HLF was similarly related to the same parameters as TLF, with total bacterial cells being the best correlated (ρs 0.64). In the subset of 22 sources, DOC clustered with TLF, HLF, and total bacterial cells, and a linear regression model demonstrated HLF was the best predictor of DOC (r2 0.84). The intergranular nature of the aquifer, timing of the study, and/or non-uniqueness of the signal to TTCs can explain the significant associations between TLF/HLF and indicators of faecal contamination such as on-site sanitation density and nutrients but not TTCs. The bacterial population that relates to TLF/HLF is likely to be a subsurface community that develops in-situ based on the availability of organic matter originating from faecal sources. In-situ fluorescence spectroscopy instantly indicates a drinking water source is impacted by faecal contamination but it remains unclear how that relates specifically to microbial risk in this setting.
Highlights
Natural organic matter (OM) is the assortment of organic, carbonaceous materials that are ubiquitous in hydrological systems (Matilainen et al, 2010)
Fluorescent OM is significantly associated with parameters linked to faecal contamination that include on-site sanitation density (OSS), NO2−/NO3−, total bacterial cells (TBCs), and dissolved organic carbon (DOC); but not with thermotolerant coliforms (TTCs), which tend to be indicative of recent contamination
It is unclear whether the lack of thermotolerant (faecal) coliforms (TTCs) association is because of: the intergranular nature of the aquifer, sampling being conducted nine months after the cessation of the recharge season, or the non-uniqueness of tryptophan-like (TLF) and humic-like fluorescence (HLF) to TTCs
Summary
Natural organic matter (OM) is the assortment of organic, carbonaceous materials that are ubiquitous in hydrological systems (Matilainen et al, 2010). Fluorescence spectroscopy is a rapid, reagentless technique that can be undertaken in-situ using portable fluorimeters (Carstea et al, 2019; Sorensen et al, 2018b). These fluorimeters are typically configured to target specific excitation-emission wavelength (λex/λem) pairs associated with either tryptophan-like (TLF) or humic-like fluorescence (HLF) HLF is typically associated with more complex allochthonous material that derives from the breakdown of vegetation, and is the dominant fluorophore in freshwater (Coble et al, 2014; Fellman et al, 2010). Studies in marine environments (Romera-Castillo et al, 2011; Shimotori et al, 2012), soils (Kallenbach et al, 2016), and the laboratory (Fox et al, 2017) show HLF can be microbially derived
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
