A comparative analysis of regional infection risk due to wastewater recontamination in the Mezquital Valley, Mexico.

Urban wastewater reuse for agriculture provides reliable nutrient-rich water, reduces water stress, and strengthens food systems. However, wastewater reuse also presents health risks and characterizing the spatial dynamics of wastewater can help optimize risk mitigation. We conducted comparative risk analysis of exposure to wastewater in irrigation canals, where we compared those exposed to a) treated vs. untreated wastewater, and b) wastewater upstream vs. downstream from communities in the Mezquital Valley. The canal system with treated wastewater was sampled prior to being treated, directly after treatment, as well as before and after it flowed through a community. Along the canal system that carried untreated wastewater, we sampled before and after a community. We quantified the concentrations of bacterial, protozoal, and viral pathogens in the wastewater. Pathogen concentration data were used to calculate measures of relative risk between sampling points. Wastewater treatment reduced predicted bacterial pathogen infection risk in post-treatment locations (RR = 0.73, 95 % CI 0.61, 0.87), with no evidence of similar reductions in Giardia or viral pathogens (RR = 1.02, 95 % CI 0.56, 1.86 and RR = 1.18, 95 % CI 0.70, 2.02 respectively). Although infection risk decreased further down the canals, infection risk increased for bacterial pathogens after our sentinel community (RR = 1.94, 95 % 1.34, 2.86). For Giardia and viral pathogens infection risk was elevated but not significantly. We found similar evidence for increases in risk when comparing the treated section of the canal system with a canal section whose wastewater was not treated, i.e., the risk benefits of wastewater treatment were lost after our sentinel community for bacteria (RR = 5.27 vs. 2.08 for sampling points before and after our sentinel community respectively) and for Giardia (RR = 6.98 vs. 3.35 respectively). The increase in risk after transit through communities could have resulted from local community recontamination of the treated wastewater stream.

Modeling Spatial Risk of Diarrheal Disease Associated with Household Proximity to Untreated Wastewater Used for Irrigation in the Mezquital Valley, Mexico.

BACKGROUND: Reusing wastewater for irrigation is a longstanding practice that enhances crop yields and improves climate resilience. Without treatment, however, wastewater contains harmful pathogens and chemicals. Reuse of untreated wastewater has been shown to be harmful to the health of nearby communities, but the routes of exposure are unknown and do not appear to be occupational. Some routes occur throughout entire communities, such as food contamination. Other routes may be spatially dependent, such as spread by domestic animals or through aerosolization. OBJECTIVES: To examine whether those wastewater exposure routes with a spatial dependency affect health, we estimated the risks of diarrheal disease in children under age 5 associated with living near wastewater canals, while adjusting for potential individual- and household-level confounders. METHODS: We conducted three surveys over 1 y in the Mezquital Valley, Mexico, to measure diarrhea in children. The distance between each participating household and a wastewater canal was measured using GPS coordinates. The association between proximity and diarrhea was estimated with a multilevel logistic regression model accounting for spatial autocorrelation. RESULTS: A total of 564 households completed one to three surveys, resulting in 1,856 survey observations of 646 children. Children living 100m from a canal had 45% lower odds of diarrhea than those living within 10m of a canal, and children living 1000m away had 70% lower odds of diarrhea [100m vs. 10m adjusted odds ratio (OR)=0.55, 95% credible interval (CI): 0.33, 0.91; 1000m vs. 10m adjusted OR=0.30, 95% CI: 0.11, 0.82]. DISCUSSION: The estimated decline in diarrheal prevalence with household distance from a canal persisted after controlling for occupational exposure. Identifying the specific routes of exposure that drive this relationship will help identify which interventions, such as upstream treatment, can reduce health risks for entire communities where wastewater exposure occurs. https://doi.org/10.1289/EHP6443.

Short-term effects of ambient temperature on non-external and cardiovascular mortality among older adults of metropolitan areas of Mexico.

Multi-city studies assessing the association between acute exposure to temperature and mortality in Latin American are limited. To analyze the short-term effect of changes in temperature (increase and decrease) on daily non-external and cardiovascular mortality from 1998 to 2014, in people 65 years old and over living in 10 metropolitan areas of Mexico. Analyses were performed through Poisson regression models with distributed lag non-linear models. Statistical comparison of minimum mortality temperature (MMT) and city-specific cutoffs of 24-h temperature mean values (5th/95th and 1st/99th percentiles) were used to obtain the mortality relative Risk (RR) for cold/hot and extreme cold/extreme hot, respectively, for the same day and lags of 0-3, 0-7, and 0-21 days. A meta-analysis was conducted to synthesize the estimates (RRpooled). Significant non-linear associations of temperature-mortality relation were found in U or inverted J shape. The best predictors of mortality associations with cold and heat were daily temperatures at lag 0-7 and lag 0-3, respectively. RRpooled of non-external causes was 6.3% (95%CI 2.7, 10.0) for cold and 10.2% (95%CI 4.4, 16.2) for hot temperatures. The RRpooled for cardiovascular mortality was 7.1% (95%CI 0.01, 14.7) for cold and 7.1% (95%CI 0.6, 14.0) for hot temperatures. Results suggest that, starting from the MMT, the changes in temperature are associated with an increased risk of non-external and specific causes of mortality in elderly people. Generally, heat effects on non-external and specific causes of mortality occur immediately, while cold effects occur within a few days and last longer.