An assessment of the human health risks posed by pathogens through various water types

Abstract

The aim of this study was to determine whether people exposed to the waters at various pOints of use in selected areas of the Mangaung Municipality, were indeed subjected to a probability of infection by the bacterial pathogen Salmonella as previous microbiological monitoring programmes in the area (based on the indicator organism E. coil) had suggested. Applying a Water-related Quantitative Microbial Risk Assessment (WRQMRA) process determined this where domestic and recreational water-use activities lead to the potential ingestion of polluted water. The WRQMRA consisted of the Observed-adverse-effect-Ievel (OAEL) and the Quantitative Microbial Risk Assessment (QMRA) approaches. The OAEL approach (OAELA) was based on the occurrence of E. coli to determine the possible risk of infection, while the QMRA predicted the probable risk of infection by Salmonellae numbers. 80th these approaches were applied to untreated surface waters, used mainly for recreational purposes, as well as to container-stored water (untreated spring water and treated municipal supply water) used for domestic purposes. The OAELA measured the E. coli numbers against various water quality guideline limits for the various water uses, while QMRA calculated the probable infection risk (PI) by applying the four risk assessment steps of hazard assessment, exposure assessment, doseresponse assessment and risk characterisation. The results of the OAELA and QMRA were compared to determine whether the use of the OAELA alone (applied by Environmental Health Practitioners) could, on a continual basis, reliably predict the risk of infection. \ Ingestion was the only exposure route investigated, based on selected volumes for the various water-uses. For recreational use of the untreated surface waters in the Renoster Spruit Quartemary Catchment (RSQC), 100mt, 50mt and 10mt were used depending o,n the level of contact with the water. Modified ingestion volumes were extrapolated for various consumer age groups ranging from infants (1,318 mt) to the elderly (865 mt). For the waters in the RSQC, the mean E. coli and Salmonellae occurrences at three sampling sites (RS1, RS2 and BS) were combined and used to calculate the risk. A single-exposure, as well as seasonal (242-day) exposure to the mean, as well as 95'h percentile risk was calculated. For untreated surface waters in the RSQC, both the OAEL and the QMRA approaches indicated a risk of infection to recreational users even for a single exposure event. However, the OAELA either over- or underestimated the risk of infection for singular exposure events and therefore could not predict a continual risk of infection. It is recommended that the full WRQMRA process be used in future. A single-exposure, as well as annual (365-days) risk of infection was calculated for the container-stored (untreated spring and treated municipal supply) water applied for domestic purposes based on the mean and reasonable maximum (95'h percentile) expected dose. Both the OAELA and the QMRA indicated a risk of infection after even a single exposure. However, the OAELA inconsistently over- or underestimated the risk on single sampling events, therefore not reliably indicating the risk of infection on its own. The full WRQMRA process is again recommended, considering several uncertainties that developed throughout the study. It was uncertain to what extent E. coli could indicate the risk of infection by Salmonellae, since it is an indicator of the potential presence of many other pathogens as well. Suitable risk limits lacked for the study area. It is recommended that the entire WRQMRA process developed for this study be applied more often in assessing risk posed by ingestion of water, but with provision for a wider range of pathogens and associated indicator micro-organisms