Temporal Variability of Faecal Contamination from On-Site Sanitation Systems in the Groundwater of Northern Thailand

Abstract

We investigated the impacts of on-site sanitation systems to local groundwater. In this year-long study, we monitored the response of faecal contamination levels to hydroclimatological factors including rainfall and groundwater table. Concentration of faecal indicators-E. coli (ESC), Enterococcus (ENT), nitrate-in thirteen pairs of shallow and deep wells were determined every 7-14 days. All samples from shallow wells were tested positive for faecal contamination (ESC and ENT > 1 MPN/100 mL) but concentration varies. A maximum of 24,000 MPN/100 mL were recorded in some shallow wells. Water from deep wells showed lower susceptibility to contamination with only 4 and 23% of samples tested positive for ESC and ENT, respectively. Concentrations of ESC and ENT were lower too, with a maximum of 5 MPN/100 mL and 28 MPN/100 mL, respectively. Fluctuation in contamination among the wells was described by four archetypal responses to hydroclimatological forcing: (i) flushing during the onset of wet season, (ii) dilution over the course of the wet season, (iii) concentration during the dry season, and (iv) synoptic response to storms. Previous studies attempting to link the prevalence of faecal/waterborne diseases and temporal factors (e.g., dry vs wet season) have produced differing outcomes. Our study may help explain the relevant hydrological mechanisms leading to these varying observations. Presently, most communities in Thailand have access to 'improved' sanitation systems. However, due to the unsustainable implementation of these systems, the otherwise viable drinking-water resources in the form of the abundant local groundwater has become a genuine health hazard.

Quantifying the effect of overland flow on Escherichia coli pulses during floods: Use of a tracer-based approach in an erosion-prone tropical catchment

“…Catchment microbial response depends on complex interactions between spatial patterns of land use, soil types, antecedent conditions of soil, and rainfall characteristics (Kim et al, 2018;McKergow and Davies-Colley, 2010;Pachepsky et al, 2018;Strauch et al, 2014). In the tropics, the presence in stream water of Fecal Indicator Bacteria (FIB), such as Escherichia coli (E. coli), is known to be partly driven by surface runoff (Causse et al, 2015;Ribolzi et al, 2016a) and groundwater flow (Chuah and Ziegler, 2018).…”

Effect of Inter-Observer Variation on the Association between Contamination Hazards and the Microbiological Quality of Water Sources: A Longitudinal Study

“…Whilst a contamination pathway such as a cracked concrete apron around a well may be present, it may not be active at the time of sampling and so not reflected in FIB counts. For example, repeated weekly testing of shallow wells for E. coli and intestinal enterococci in Thailand suggests that transient contamination peaks may be missed by cross-sectional sampling [ 38 ], with similar temporal variability in FIB from a study of shallow wells in Cambodia [ 39 ]. Our protocol involved tracing water sources used for drinking by participating households in different seasons.…”

Culture of fecal indicator bacteria from snail intestinal tubes as a tool for assessing the risk of Opisthorchis viverrini infection in Bithynia snail habitat

“…We see several potential applications of snail gut culture for fecal indicator bacteria in the context of O. viverrini . First, we suspect that rainfall plays a key role in the mobilization and transport of O. viverrini eggs, present in fecal waste, to snail habitat [30, 31]. Coupled longitudinal sampling of fecal indicator bacteria in water and snail gut contents can help shed light on the pulses of fecal contaminants that lead to direct snail exposure to fecal waste.…”