Measuring Human Sewage Contamination in Surface Waters Using Human and Bacterial DNA Markers

Fecal pollution in urban surface waters can be caused from various point sources such as industrial and municipal sewage effluent. Non-point sources of fecal pollution include illegal wastewater discharges, sewer overflow and septic tank seepage, wildlife waste and land runoff from animal feedlots. To identify the sources of fecal contamination Microbial Source Tracking (MST) methods are used broadly. A widely used indicator of microbial water contamination is the coliform group of microorganism such as fecal coliforms, Escherichia coli (E. coli) and/or Enterococcus spp. These fecal indicator bacteria serve as standard monitoring tools for establishing risks to public health in surface waters.

Upper Cibolo Creek flows through the Cibolo Preserve area and has a history of exceeding the bacterial contamination of safe contact recreation level applied by the state standard guideline. Moreover, South Texas Wastewater Treatment Plant (WWTP) and Wastewater Treatment and Recycling Center (WWTRC) of Boerne, TX discharge their effluent water directly into the creek upstream of the preserve. In this study, human mitochondrial DNA as a direct marker and human-specific Bacteroidales (HF183 and BacHum) were used to detect the human fecal contamination in Cibolo Creek within the preserve. Previous studies have shown higher manure deposition near the creek area from different animal and livestock. To evaluate the current situation of such non-point contaminations, E. coli was also used as a fecal indicator bacteria.

A total of 9 sampling sites were investigated bi-weekly for a period of ten months and quantitative PCR assays were obtained with the concentration ranges of (0.00-4.96) log10 copies/100ml for E. coli, (0.00 – 6.69) log10 copies/100ml for human mtDNA, (0.00 – 4.89) log10 copies/100ml for HF183, and (0.00 - 4.39) log10 copies/100ml for BacHum. Moreover, the South Texas Wastewater Treatment Plant (WWTP) influenced higher occurrence for all four markers in the nearby site. One way ANOVA and Tukey’s HSD test obtained a significant difference of occurrences for the site after South Texas WWTP with the other sites (P<0.001) for BacHum, HF183 and E. coli. BacHum and HF183 obtained a strong Pearson’s correlation coefficients of 0.79 and 0.76 with E. coli indicated human fecal pollution near the preserve area. As the precipitation data obtained very low (≤0.10) correlation and flow obtained positive (0.10-0.30) correlation with the markers concentration, the main sources of human fecal pollution were the flow from the Upper Cibolo Creek and the WWTPs.