Strength in Numbers

Global public health is a collaborative business. At a workshop in Mexico City this morning, scientists from two countries (U.S. and Mexico) and two universities (U-M and the Universidad Nacional Autónoma de México) gathered with representatives of the National Institute of Public Health in Mexico and a representative of the Mexican government to discuss a massive wastewater treatment project scheduled to begin this year in a valley north of Mexico City.

For more than 100 years, farmers in Mexico’s Mézquital Valley have used untreated wastewater from Mexico City to irrigate crops—chiefly corn and alfalfa. Scientists have long been interested in the risks posed by this system, both for human health and for the environment, but until now they’ve been unable to get a clear picture of those risks, in part because the exposure pathways are complex and difficult to measure. When the wastewater treatment opens later this year, it will present a veritable laboratory for scientific inquiry—especially because some communities in the valley will receive treated wastewater and others will continue receiving untreated wastewater. Among the questions researchers want to address:

  • What impact will the plant have on the incidence of diarrheal diseases in children who live in communities that receive treated wastewater?
  • What effect will the change have on tap water and dust in households exposed to treated wastewater, versus households that are exposed to untreated wastewater?
  • How will the introduction of treated wastewater affect the presence of enteric pathogens and antibiotic resistance in communities in Mézquital Valley?
  • How will the introduction of treated wastewater affect the environment, including soil?

Organized to help design research studies around these questions, today’s workshop in Mexico City drew geologists, microbiologists, ecologists, epidemiologists, and policymakers. Discussions ranged back and forth between Spanish and English.

The launch of the wastewater treatment plant is an important development, says SPH’s Joseph Eisenberg, chair of the Department of Epidemiology, who with SPH Assistant Professor Rafael Meza will conduct a longitudinal study of the health impacts of the plant. Eisenberg notes that worldwide, thanks to growing urbanization, there’s more wastewater than ever before, and little if any of it is treated. But no city produces more wastewater for agricultural use than Mexico City, and so findings from Mézquital have global implications. Research from Mézquital informed the original guidelines for wastewater re-use set by the World Health Organization in 2006 and will inform a planned revision of those guidelines.

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