Household water quality in areas irrigated with wastewater in the Mezquital Valley, Mexico.

Wastewater for irrigation in low- and middle-income countries can recharge aquifers and potentially contaminate supply sources. The infiltration rate has increased 13-fold in Mexico's Mezquital Valley, the largest agricultural area wastewater-irrigated worldwide, thus we assume that wastewater had contaminated supply sources. Fecal indicator bacteria (FIB) counts were enumerated in household water of two wastewater-irrigated areas, Tula and Tlahuelilpan, and a groundwater irrigated area, Tecozautla. During 2016-2017, household water, wastewater, and groundwater were sampled, analyzing fecal coliforms, fecal enterococci, and Escherichia coli, following membrane filtration procedures, and confirming the presence of E. coli by polymerase chain reaction. Nearly 50% of household water contained fecal contamination of up to 4.62 × 104 CFU/100 mL. Significant differences between FIB counts in household water from Tula and Tecozautla were observed by Kruskal-Wallis and Dunnett tests. Household water samples from Tula contained highest FIB counts. Wastewater from Tula and Tlahuelilpan contained counts of six orders-of-magnitude of FIB. Counts were high when residual chlorine was <0.2 mg L-1 and underwater storage. This research serves as a baseline to observe improvement with a newly installed wastewater treatment plant. Safe irrigation wastewater reuse should be performed under strict surveillance, considering human safety a priority.

Health risks from exposure to untreated wastewater used for irrigation in the Mezquital Valley, Mexico: A 25-year update.

Wastewater reuse for agriculture is common worldwide; wastewater treatment, however, is rare in many countries, leading to high potential for exposure to harmful pathogens. Mexico City, one of the largest producers of untreated wastewater for agricultural use worldwide, was the site of key epidemiologic studies conducted in the 1990s. We both reviewed the literature on and conducted a cross-sectional study of diarrheal risk and wastewater contamination to provide an updated assessment of health risks and to inform an upcoming update of the 2006 WHO guidelines on wastewater reuse. We surveyed communities in the Mezquital Valley that use wastewater for irrigation and communities that use well water to compare the prevalence of self-reported diarrheal disease in children under five years old. Wastewater, well water, household environmental samples, and stool samples were collected and analyzed. Communities exposed to wastewater had a higher one-week prevalence of diarrhea (10%) compared to unexposed communities (5%). This association remained in an adjusted modified Poisson regression model (PR = 2.31, 95% CI 1.00, 5.31), but not when limited to households engaged in agriculture. Water quality indicators document differences between irrigation water from the two community groups. These results are in agreement with 25 population studies identified by our review that were conducted since or not included in the 2006 WHO guidelines and show consistent negative impacts of wastewater exposure on health. While overall diarrheal prevalence has declined when compared to studies conducted over 25 years ago in the same region, the association of diarrheal disease and wastewater exposure has remained and possibly increased. With rising urbanization worldwide, attention to these risks and wastewater treatment is becoming increasingly important.