The US deports more Mexicans to Tijuana than any other borderland city. Returning involuntarily as members of a stigmatized underclass, many find themselves homeless and de-facto stateless. Subject to routinized police victimization, many take refuge in the Tijuana River Canal (El Bordo). Previous reports suggest Tijuana River water may be contaminated but prior studies have not accessed the health effects or contamination of the water closest to the river residents. A binational, transdisciplinary team undertook a socio-environmental, mixed methods assessment to simultaneously characterize Tijuana River water quality with chemical testing, assess the frequency of El Bordo residents’ water-related diseases, and trace water contacts with epidemiological survey methods (n = 85 adults, 18+) in 2019, and ethnographic methods in 2019–2021. Our analysis brings the structural violence framework into conversation with an environmental injustice perspective to documented how social forces drive poor health outcomes enacted through the environment. The Tijuana River water most proximate to its human inhabitants fails numerous water-quality standards, posing acute health risks. Escherichia coli values were ∼40,000 times the Mexican regulatory standard for directly contacted water. Skin infections (47%), dehydration (40%) and diarrhea (28%) were commonly reported among El Bordo residents. Residents are aware the water is contaminated and strive to minimize harm to their health by differentially using local water sources. Their numerous survival constraints, however, are exacerbated by routine police violence which propels residents and other people who inject drugs into involuntary contact with contaminated water. Human rights to drinking water, sanitation and hygiene are routinely violated among El Bordo in-habitants. This is exacerbated by violent policing practices that force unhoused deportees to seek refuge in waterways, and drive water contacts. Furthermore, US-Mexico ‘free-trade’ agreements drive rapid growth in Tijuana, restrict Mexican environmental regulation enforcement, and drive underinvestment in sewage systems and infrastructure.

In rapidly growing urban areas, such as Tijuana, Mexico, the presence of urban green spaces (UGSs) can help stem soil erosion, improve infiltration, slow runoff, decrease flooding, reduce air pollution, and mitigate climate change. In many water-scarce parts of the world, where centralized wastewater treatment is not accessible or practical, decentralized wastewater treatment systems (DEWATSs) have the potential to supply the water needed for irrigating UGSs. Here, we first review UGS systems supported by DEWATSs and the water quality guidelines and challenges associated with implementing DEWATSs for urban greening in different countries, including Mexico. We also critically examine the linkages between the lack of UGSs in Tijuana, Mexico, extensive soil erosion, and failing sanitation infrastructure that has led to the infamously poor water quality in the Tijuana River. Tijuana’s Ecoparque Wastewater Treatment Facility, a low-energy, aerobic DEWATS, which collects, treats, and discharges residential sewage for localized landscape irrigation, demonstrates how DEWATSs can meet the water demands for urban greening in rapidly urbanizing cities. The aerobic decentralized treatment using a gravity-fed trickling biofilter resulted in a >85% removal of chemical oxygen demand and dissolved organic carbon. Prior to treatment facility upgrades, there was a ~2 log reduction in total coliform and Escherichia coli and a <20% decrease in ammonia from the influent to final effluent. After the addition of a maturation pond in 2020, the effluent met Mexico standards for irrigation reuse, with a ~4 log reduction in fecal coliforms from the influent to final effluent. Case study results demonstrated the potential for decentralized wastewater treatment to meet effluent standards for landscape irrigation, provide water for urban greening, and prevent pollution in the Tijuana River and other urban waterways.

Delays and community traffic problems associated with US–Mexican border ports of entry have been criticized for causing economic losses and increasing social stressors. This paper draws attention to an overlooked issue, the potential for adverse health effects associated with being exposed to localized high levels of traffic pollutants on border crossers and nearby communities at ports of entry along the US–Mexican border. The literature on health effects of exposure to near-road traffic pollution is incorporated into an analysis of the situation along the US–Mexican border. This paper synthesizes the information available regarding excessive wait times at the border and describes preliminary studies linking these delays to elevated traffic pollution levels. We frame exposure to traffic pollutants at US–Mexican ports of entry as an environmental justice issue in that the burden of exposures and associated risks of health effects is borne by nearby low income minority communities. Mitigation strategies are explored and reduction of border crossing wait times is identified as the most feasible action. Adverse effects of exposure to near traffic pollution are likely applicable to congested borders throughout the world.

Environmental issues at the U.S.–Mexico border have been approached in a fragmented way and considered of minor political interest; even though they have been addressed in treaties and agreements, regional environmental pollution persists. One may ask what sort of measures should be taken to address the complex and long-term environmental problems in the U.S.–Mexico border region. To answer this question, an environmental cross-border governance proposal was evaluated by applying Qualitative Analysis of Textual Data to the text of Chapter 24 of the USMCA treaty. The results indicated that the environmental policies concerning the border region still lack a coherent systemic approach, and hence will lead to inefficiency. Territorial development is heavily dependent on national environmental governance and priorities; however, environmental issues should be understood in an integral, complex and deeply entangled way if they are to be effectively addressed. Otherwise, environmental degradation is likely to expand due to population growth and events associated with climate change.