BACTERIAL AND VIRAL INDICATORS OF FECAL POLLUTION IN MEXICO CITY'S SOUTHERN AQUIFER

摘要

Mexico City with a population of about 18 million people relies on groundwater to supply about 70/100 of its water needs. In order to understand the extent of microbial pathogen contamination of these reserves, a 10 month long monitoring study of the southern aquifer was undertaken. Groundwater samples were collected from five different locations and analyze (100 mL) for total coliforms, fecal coliforms , and fecal streptococci. Larger volume samples (5 L) were collected and concentrated for quantitative and qualitative (presence/absence) determination of microorganisms including bacteriophages. Gene amplification (PCR) approaches were employed to screen for Escherichia coli/Shigella specific (uid) sequences. Laboratory microcosms were conducted to evaluate the potential survival of pathogenic viruses in the groundwater using MS-2 and PRD-1 as model viruses. Coliphage as a single indicator, or in conjunction with fecal coliforms and fecal streptococci were found to have value as an indicator of fecal pollution in this geographical region. The results indicate that the southern aquifer underlying metropolitan Mexico City can pose a significant risk to public health when water is distributed and used without adequate disinfection. The pumping wells located in the transition and mountain areas indicated the presence of extensive microbial pathogen contamination. There was surprisingly, no difference between the dry and rainy seasons in terms of the presence of fecal pollution microbial indicators.