Microbiological Implications of Periurban Agriculture and Water Reuse in Mexico City

BACKGROUND: Recycled treated or untreated wastewater represents an important health challenge in developing countries due to potential water related microbiological exposure. Our aim was to assess water quality and health implications in a Mexico City periurban agricultural area. METHODOLOGY/PRINCIPAL FINDINGS: A longitudinal study in the Xochimilco wetland area was conducted, and 42 sites were randomly selected from 211, including irrigation water canals and effluents of treatment plants. Sample collection took place during rainy and dry seasons (2000-2001). Microbiological parameters (total coliforms, fecal coliforms, streptococci/enterococci, and bacteria other than Vibrio grown on TCBS), Helicobacter pylori, and physicochemical parameters including trihalomethanes (THM) were determined. Fecal coliforms and fecal streptococci are appropriate indicators of human or animal fecal contamination. Fecal coliform counts surpass Mexican and World Health Organization irrigation water guidelines. Identified microorganisms associated with various pathologies in humans and domestic animals comprise Escherichia coli, Klebsiella spp., Salmonella spp., Enterobacter spp., Enterococcus spp., and Pseudomonas spp; H. pylori was also present in the water. An environmental characteristic of the canal system showed high Total Organic Carbon content and relatively low dissolved oxygen concentration; residual chlorine as a disinfection control is not efficient, but THMs do not represent a problem. During the rainy season, temperature and conductivity were higher; in contrast, pH, dissolved oxygen, ammonia, and residual chlorine were lower. This is related with the continuous load of feces from human and animal sources, and to the aquatic systems, which vary seasonally and exhibit evidence of lower water quality in effluents from treatment plants. CONCLUSIONS/SIGNIFICANCE: There is a need for improvement of wastewater treatment systems, as well as more efficient monitoring, regulation, and enforcement procedures for wastewater disposal into bodies of water

Quantifying the Reduction in Potential Health Risks by Determining the Sensitivity of Poliovirus Type 1 Chat Strain and Rotavirus SA-11 to Electron Beam Irradiation of Iceberg Lettuce and Spinach

Fresh produce, such as lettuce and spinach, serves as a route of food-borne illnesses. The U.S. FDA has approved the use of ionizing irradiation up to 4 kGy as a pathogen kill step for fresh-cut lettuce and spinach. The focus of this study was to determine the inactivation of poliovirus and rotavirus on lettuce and spinach when exposed to various doses of high-energy electron beam (E-beam) irradiation and to calculate the theoretical reduction in infection risks that can be achieved under different contamination scenarios and E-beam dose applications. The D(10) value (dose required to reduce virus titers by 90%) (standard error) of rotavirus on spinach and lettuce was 1.29 (± 0.64) kGy and 1.03 (± 0.05) kGy, respectively. The D(10) value (standard error) of poliovirus on spinach and lettuce was 2.35 (± 0.20) kGy and 2.32 (± 0.08) kGy, respectively. Risk assessment of data showed that if a serving (∼14 g) of lettuce was contaminated with 10 PFU/g of poliovirus, E-beam irradiation at 3 kGy will reduce the risk of infection from >2 in 10 persons to approximately 6 in 100 persons. Similarly, if a serving size (∼0.8 g) of spinach is contaminated with 10 PFU/g of rotavirus, E-beam irradiation at 3 kGy will reduce infection risks from >3 in 10 persons to approximately 5 in 100 persons. The results highlight the value of employing E-beam irradiation to reduce public health risks but also the critical importance of adhering to good agricultural practices that limit enteric virus contamination at the farm and in packing houses

Comparative study of enteric viruses, coliphages and indicator bacteria for evaluating water quality in a tropical high-altitude system

<p>Abstract</p> <p>Background</p> <p>Bacteria used as indicators for pathogenic microorganisms in water are not considered adequate as enteric virus indicators. Surface water from a tropical high-altitude system located in Mexico City that receives rainwater, treated and non-treated wastewater used for irrigation, and groundwater used for drinking, was studied.</p> <p>Methods</p> <p>The presence of enterovirus, rotavirus, astrovirus, coliphage, coliform bacteria, and enterococci was determined during annual cycles in 2001 and 2002. Enteric viruses in concentrated water samples were detected by reverse transcriptase-polymerase chain reaction (RT-PCR). Coliphages were detected using the double agar layer method. Bacteria analyses of the water samples were carried out by membrane filtration.</p> <p>Results</p> <p>The presence of viruses and bacteria in the water used for irrigation showed no relationship between current bacterial indicator detection and viral presence. Coliphages showed strong association with indicator bacteria and enterovirus, but weak association with other enteric viruses. Enterovirus and rotavirus showed significant seasonal differences in water used for irrigation, although this was not clear for astrovirus.</p> <p>Conclusion</p> <p>Coliphages proved to be adequate faecal pollution indicators for the irrigation water studied. Viral presence in this tropical high-altitude system showed a similar trend to data previously reported for temperate zones.</p

Evaluation of ecological quality in peri-urban rivers in Mexico City: a proposal for identifying and validating reference sites using benthic macroinvertebrates as indicators

Conservation and management of aquatic ecosystems that are significantly influenced by urban activities requires the classification and establishment of potential reference sites. However, in Latin American countries, policies are not available that outlines the identification and evaluation of such sites. Therefore, this study represents a proposal for evaluating the ecological quality of peri-urban rivers in the conservation soil (CS) areas/zones of Mexico City. The proposal accounts for the zone’s physicochemical, hydromorphological, and bacteriological characteristics along with its macroinvertebrate richness. Our evaluation was performed using a canonical correspondence analysis (CCA) and indicator values (IndVal) calculated for different species. River headwaters serve/work as a good physicochemical point for potential references sites. However, the hydromorphology of the CS has been gradually modified by numerous hydraulic alterations within the peri-urban zone. Using the CCA and IndVal, two types of sites were confirmed: sites in a good state of conservation and quality and sites modified by human activity, featuring lower discharge flow, poor quality hydromorphological values and Oligochaeta class organisms. At the sites featuring a good state of conservation and quality, higher hydromorphological values were positively correlated with discharge flow and certain macroinvertebrate taxa, including Nemouridae, Podonominae, Tanypodinae, Acarina, Baetis, Tipula, Antocha, Atopsyche, Glossosoma, Polycentropus, Hesperophylax and Limnephilus. In the sites modified by human activity, the genus Simulium was classified as a disturbance-tolerant organism. The river reach within the urban zone is basically an open-air drainage ditch. Evaluations of the ecological quality of the riparian zone were used to identify the most important hydromorphological qualities and discharge flow parameters and to select the most appropriate factors that should be monitored in peri-urban rivers of the Mexico Basin. </p

Entidades de la Zona Metropolitana de la Ciudad de México propensas a la contaminación de agua subterránea

El 70% del agua que se utiliza en la Zona Metropoiitana de la Ciudad de México (ZMCM) destinado al uso doméstico industrial v agrícola, proviene de los sistemas de acuiferos de la Cuenca de México, por lo que es imooriante conocer las fuentes de contaminación que pueden influir en la calidad del recurso. En este estudio se realiza un análisis especial, a nivel de delegación y municipio, de las principales fuentes contaminantes del agua subterránea, con el objeto de identificar zonas propensas a la contaminación. Se tomaron como fuentes contaminantes la industria, los confinamientos de residuos sólidos, los depósitos de combustible, el sistema de drenaje, las gasolineras, los pozos de extracción y la zona urbanizada. La distribución de las fuentes contaminantes. aunada a las zonas geológicas principales que subyacen a la ciudad, permitió determinar que el centro de la ZMCM presentaba la mayor concentración de fuentes contaminantes, mientras que la mayor propensión a la contaminación para el sistema de acuiferos se encontró hacia el sur-poniente y norte de la ZMCM

Sustainability of Least Cost Policies for Meeting Mexico City\u27s Future Water Demand

Meeting future water demand without degrading ecosystems is one important indicator of sustainable development. Using simulations, we showed that compared to existing policy, more sustainable water supply options are similar or cheaper in cost. We probabilistically forecasted the Mexico City metropolitan zone population for the year 2015 to be 23.5 million and total required water supply to be 106 m3 s-1. We optimized existing and potential supply sources from aquifers, surface water, treatment/reuse, and efficiency/demand management by cost to meet future supply needs; the applied source supply limits determined the degree of sustainability. In two scenarios to supply 106 m3 S-1, the business-as-usual scenario (zero sustainability) had an average relative unit cost of 1.133; while for the most sustainable scenario (it includes reducing potential supply basins\u27 exploitation limits by 50%), the value was 1.121. One extreme scenario to supply the forecast\u27s 95% confidence value (124 m3 s-1) showed little unit cost change (1.106). The simulation shows sustainable policies can be cost-effective

Illustrating climate-change resilience engineering: Conceptual design of water supply and wastewater/stormwater system for the México-Lerma-Cutzamala hydrological region

Conventional engineering education, research, and practice need to be transformed in the face of growing, complex climate-change impacts to populations and landscapes.New approaches that integrate diverse types of knowledge–engineering, natural science, social science, humanities, professional, Indigenous, and lived experience -- need to be mobilized in collaborative ways. Volume 1 in the series Integrated Global STEM