Redalyc.Microbiological Indicators of Water Quality in the Xochimilco
Total Page:16
File Type:pdf, Size:1020Kb
Salud Pública de México ISSN: 0036-3634 [email protected] Instituto Nacional de Salud Pública México Juárez, Luis Alfredo; Silva, Jesús; Uribe, Felipe Javier; Cifuentes, Enrique Microbiological indicators of water quality in the Xochimilco canals, Mexico City Salud Pública de México, vol. 45, núm. 5, septiembre-octubre, 2003, pp. 389-395 Instituto Nacional de Salud Pública Cuernavaca, México Available in: http://www.redalyc.org/articulo.oa?id=10645509 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Microbiological indicators of water quality in Xochimilco ARTÍCULO BREVE Microbiological indicators of water quality in the Xochimilco canals, Mexico City Luis Alfredo Juárez-Figueroa, MD,(1) Jesús Silva-Sánchez, PhD, (1) Felipe Javier Uribe-Salas, MD, MPH, MSc,(1) Enrique Cifuentes-García, PhD.(1) Juárez-Figueroa LA, Silva-Sánchez J, Juárez-Figueroa LA, Silva-Sánchez J, Uribe-Salas FJ, Cifuentes-García E. Uribe-Salas FJ, Cifuentes-García E. Microbiological indicators of water quality Indicadores microbiológicos de la calidad del agua in the Xochimilco canals, Mexico City. de los canales de Xochimilco de la Ciudad de México. Salud Publica Mex 2003;45:389-395. Salud Publica Mex 2003;45:389-395. Abstract Resumen Objective. To quantify microbiology indicators of fecal con- Objetivo. Cuantificar diversos indicadores de contami- tamination in the effluents of two waste water treatment nación fecal en los efluentes de dos plantas de tratamiento plants and in samples collected in several canals in Xochi- de aguas residuales y en muestras recogidas en varios canales milco. Material and Methods. A cross sectional study was de Xochimilco. Material y métodos. Estudio transversal performed. Ten sites, 5 from plant effluents and 5 from ca- efectuado en Xochimilco, México. Durante noviembre y di- nals, were selected for sampling during November and ciembre de 2001 se muestrearon 10 sitios, cinco efluentes December 2001. Fecal coliforms and enterococci were quan- y cinco canales, para la cuantificación de coliformes feca- tified by membrane filtration, male specific (F+) and somatic les y enterococos (filtración en membrana de nitrocelu- coliphages by double agar layer technique, and Cryptosporid- losa), colifagos somáticos (técnica de doble capa de agar), ium oocysts and Giardia cysts by concentration with Enviro- ooquistes de Cryptosporidium sp. y quistes de Giardia sp. (con- check filter followed by immunofluorescence microscopy centración en filtros Envirocheck y microscopía de inmu- quantification.The average of organisms counts from efflu- nofluorescencia). Se efectuó comparación de los promedios ents and canal water were compared with t Student test. de las cuentas de organismos hallados, en efluentes y canales, Results. Treated water discharge in canals showed a low mediante t de Student. Resultados. El agua tratada que des- count of Fecal Coliforms (average 40.4/100 ml), enterococ- carga en los canales mostró cantidades bajas de coliformes ci (average 58.8/100 ml) and Cryptosporidium oocysts (aver- fecales (media de 40.4/100 ml), enterococos (media de 58.8/ age 13.2/100 l), while coliphages and Giardia cyst rendered 100 ml) y quistes de Cryptosporidium (media de 13.2/100 l), higher counts (average 1467.5/100 ml and 1199.8/100 l, re- mientras que los colifagos y quistes de Giardia estuvieron spectively) suggesting the water treatment methods could presentes en gran cantidad (media de 1467.5/100 ml y fail to remove these agents. A significant lower count of 1199.8/100 l, respectivamente), sugiriendo que el tratamiento Giardia cysts (average 45/100 l) and no Cryptosporidium del agua puede ser ineficaz para remover estos agentes. En oocysts were found in irrigation canals, which suggests a los canales de irrigación de vegetales se encontró una can- natural clearance of these pathogens. Strains of Escherichia tidad significativamente menor de quistes de Giardia (media coli isolated in one of the canals contaminated with sewage de 45/100 l) y no se encontraron ooquistes de Cryptospori- had antimicrobial multi-resistance that was transferred by dium, lo que sugiere la remoción natural de estos agentes. conjugation suggesting that resistance is encoded in a plas- Algunos aislamientos de E coli obtenidos de un canal con- mid potentially transferable to other pathogenic bacteria. taminado con descargas cloacales mostraron una multirre- This study was financed by the Instituto Nacional de Salud Pública, México and by the University of South Florida, USA. This work was undertaken during a sabbatical at the University of South Florida, USA. (1) Instituto Nacional de Salud Pública. Cuernavaca Morelos, México. Received on: January 20, 2003 • Accepted on: August 1, 2003 Address reprint request to: Luis Alfredo Juárez-Figueroa. Instituto Nacional de Salud Pública. Avenida Universidad 655 colonia Santa María Ahuacatitlán, 62508 Cuernavaca, Morelos, México. Email: [email protected] salud pública de méxico / vol.45, no.5, septiembre-octubre de 2003 389 ARTÍCULO BREVE Juárez-Figueroa L y col. Conclusions. Cost effective and culturally acceptable sistencia a antibióticos que fue transferida por conjugación waste treatment methods will require careful planning and a otras bacterias mediante plásmidos. Esto sugiere la posible consultation if they are to be adopted and mantained by diseminación de la resistencia a bacterias del medio (posi- local populations. bles patógenas). Existen numerosos asentamientos humanos cercanos a las chinampas que descargan desechos direc- tamente a los canales. Conclusiones. La implantación de métodos de tratamiento de excretas que resulten costea- bles y culturalmente aceptables debe realizarse mediante una cuidadosa planeación y consulta, si estos métodos han de ser adoptados y sostenidos por la población local. Key words: water quality; fecal contamination; sanitation; Palabras clave: calidad del agua; contaminación fecal; sa- Mexico neamiento; México exico City’s wastewater system includes multi- turn to using partially treated wastewater. In addition, M ple open sewer canals, sewer reservoirs, lagoons, open canals are subject to non-point source illegal dis- pumping stations, and deep drainage systems. Ap- charge from farms and new homesteads. 3 The water proximately 75% of the population has access to this source for agricultural production is crucial in these wastewater system, while the rest dispose of their areas, since vegetables grown in Xochimilco are com- sewage through septic tanks and absorption wells. mercialized for consumption throughout Mexico City. Twenty seven wastewater treatment plants treat The effect of point source contamination from ir- approximately 7% of the wastewater generated in regular settlements and leakage from the overwhelmed Mexico City. However, these plants generally operate public sewage system could cancel out the expected at less than 50 percent efficiency, treating 4.3 m3/sec. effect of treatment plants installed for maintenance of Untreated wastewater irrigation of vegetables the irrigation needs for crops grown on “chinampas”. which may be eaten raw is not allowed, whereas a Additionally, this contamination could facilitate range of crops (i.e. cereals and fodder) can be irrigated the transmission of enteropathogenic agents through with an effluent containing no more than 1 000 FC per contaminated crops and through direct contact with 100 ml.1,2 Some farm settings in Mexico receive waste- agricultural workers. water meeting quality recommendations. One of the During a previous study, we encountered a high most important sites is Xochimilco, where the effluent prevalence of Giardia intestinalis infection among as- (5m3/sec) from a secondary treatment plant (activated ymptomatic children from urban settlements in the sludge process and chlorination) flows through the Xochimilco area. This infection is endemic in this area.* canals and is used for irrigation of flowers, fodder, Another agricultural area receiving most of the maize and vegetables, and aquifer recharge. wastewater generated in Mexico City, the Mezquital Xochimilco is located along the southeast edge of Valley, has a high prevalence of Giardia infections Mexico City, and is the remnant of a pre-Hispanic farm- among children. 4 ing system initiated during the 13th century on the Despite the increasing importance of this problem, edge of a lake basin. Clusters of agricultural plots (“chi- there is a surprising lack of data addressing the health nampas”), enclosed by interwoven poles of reeds and risks associated with the microbiological quality of ir- framed by canals, result in a highly efficient irrigation rigation water in Xochimilco. scheme. These plots were originally built by accumu- The present study provides baseline data on the lating layers of mud, dredged from the bottom of the microbiology quality of water in Xochimico canals us- lake, and then deposited upon marshes or shallow lake ing diverse indicators for fecal contamination and pres- areas. The case of Xochimilco is an example of the grow- ing conflict regarding availability of groundwater be- tween cities and the countryside. Increasing volumes * Cifuentes E, Suárez L, Espinoza M, Juárez-Figueroa L, Martínez- Palomo A. The risk of Giardia intestinalis. Infection in children from of groundwater are extracted for Mexico City’s