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Over the past 30 years, the population of the U.S.-Mexico border region has drastically increased. Infrastructure development, however, hasn’t followed at the same pace. The lack of municipal water treatment and controlled sanitation practices in the border region has resulted in a surge of waterborne disease as well as adverse ecological impacts, which experts fear will continue to worsen.

A vast span
The border between the United States and Mexico spans from the Pacific Ocean to the Gulf of Mexico, amounting to approximately 2,100 miles. The border “region” includes 100 kilometers (km) -- 62 miles -- both north and south of the border itself. The area is located within seven major surface watershed basins including the Pacific Coastal, New River, Gulf of California Coastal, Colorado River, Northwest Chihuahua, Rio Grande, and Gulf of Mexico Coastal Basins. Although the majority of the region is considered to be arid, there’s a wide range of ecosystems and vegetation types including freshwater and marine water environments, wetlands, deserts, rangelands, mountains and forests.

Currently, the U.S.-Mexico border population is around 12.6 million people. Population projections estimate this number will increase to 20 million by 2020. Population increases tax existing infrastructure including drinking water supplies, treatment plants and wastewater disposal facilities, and many are inadequate. Currently, at least 9 percent of the border populace is without public water supply, 23 percent lack wastewater collection, and 40 percent have no wastewater treatment. Estimates put 300,000 people without adequate sanitation and drinking water supplies on the U.S. side of the border.

Binational concerns
The majority of the population that spans the U.S.-Mexico border live in connected cities, known as “sister city” pairs. Unique environmental and public health issues affect both sides of the border. Although lower labor and assembly costs and less strict environmental regulations on wastes have contributed to the steady growth of “maquiladoras” (American-operated assembly plants with “twin” plants on the U.S. side), waste from human and industrial practices commonly seep northward across the border. Currently, there are more that 2,200 maquiladoras along the border region. Heavy metals, arsenic, lead, pesticides, uranium, etc., have all been found in excessive levels in soils and source waters on the border region. Due to significant public health or ecological impacts, the areas of high priority for control include Tijuana, Mexicali and Nogales. Contamination of the Rio Grande is also of great concern. In addition to human and industrial wastes, run-off from agricultural practices contribute significant levels of toxic compounds and nutrient overload to already stressed ecosystems. The shortage of water in arid regions of the border often correlates with a lack of proper hygiene and sanitation practices.

Little data are available assessing the varied impacts from cross-border pollution. A 1992 study by the U.S. Army Corps of Engineers estimated major Mexican cities along the Texas border discharged 175 million gallons per day (mgd) of wastewater into the Rio Grande or the Laguna Madre, wetlands that flow north of where the river empties into the gulf. The majority of this was untreated. When treated, primary settling was the only method used, leaving high levels of toxic compounds and microbial pathogens. Other studies have found that up to 23 percent of borderland drinking water contains fecal coliform levels that exceed recommended limits. Muchconcern has been raised over the discharge of untreated wastewater into the Tijuana River due to pollution flowing into Imperial Beach near San Diego. Such events have economic, public health and ecological impacts. Wastewater discharged into the Nogales Stream has been found to cross the border to the north, contaminating the Santa Cruz River in Arizona. About 3 mgd is discharged daily in this area.

Control measures are needed north of the border as well, considering that water from the Colorado River flowing into Mexico is often so high in salinity and nutrients that it isn’t applicable for designated uses such as crop irrigation. In addition, a significant number of housing developments in the border region of the United States are unincorporated subdivisions -- known as “colonias” -- characterized by low-income demographics, substandard housing and inadequate plumbing, sanitation and clean water supplies. Living conditions in the colonias are similar to those in Third World countries. Although a few are thought to exist in Arizona and California, approximately 1,200 (or the majority) are in Texas and New Mexico. Colonias are especially concentrated in Las Cruces, N.M.; El Paso, Texas, and the lower Rio Grande Valley in areas around Brownsville, Texas. Formation of the colonias dates prior to 1950 when developers sold small land plots without water and sewer infrastructure. After 1989, authorities in Texas and New Mexico required water and sewer in new developments.

Increased disease rates
Limited monitoring data from transboundary and boundary waters show high fecal coliform -- indicators of fecal contamination -- in the Tijuana River, Pacific Ocean, New River, Colorado River, San Pedro River, Santa Cruz River and the Rio Grande. The presence of fecal indicators isn’t surprising given that the rate of many waterborne infectious diseases are several times higher in the U.S.-Mexico border. The rate of Hepatitis A and Shigellosis is three times higher on the U.S. side of the border compared to the rest of the nation. Higher levels of amebiasis (amoebic dysentery), Salmonella, and other waterborne diseases are also noted. Meanwhile, the numbers increase dramatically south of the border.

Experts are concerned about the resurgence of vaccine-preventable communicable diseases and other infectious conditions along the border due to differences in immunization delivery and vaccination schedules between the two countries, differences in surveillance and reporting practices (that make binational comparisons difficult), and poor sanitaryconditions on both sides of the border that could lead to the re-emergence of infectious diseases like dengue and cholera. These issues aren’t confined to those living along the border. According to the World Health Organization, approximately one million people cross the U.S.-Mexico border daily. The ease of travel facilitates the spread of microbial pathogens to global proportions.

Future investment
The installation and rehabilitation of treatment plants and reuse options are helping to address the aforementioned problems in the border region. The United States and Mexico have both made major financial commitments to improve the quality of life in these areas. Together, the United States and Mexico are estimated to have invested nearly $1 billion in the last decade. Congress continues to appropriate hundreds of millions of dollars to border infrastructure development; however, estimates of need range from $4.5-to-8 billion.

Border improvement projects currently under way are valued at $852 million, made possible by cooperative efforts between the U.S. Environmental Protection Agency, the National Water Commission of Mexico, the Binational International Boundary and Water Commisision, the Border Environmental Cooperation Commission (BECC) and the North American Development Bank (NADBank). In March, Presidents Bush and Vicente Fox directed a binational working group to hold a series of discussions with states, communities, and other stakeholders in the border region to develop recommendations that would strengthen the NADBank and BECC. The BECC and NADBank were established in 1993 under NAFTA by the United States and Mexico to develop, certify (BECC) and finance (NADBank) infrastructure projects within 100 km (62 miles) of the border. Some of the recommendations of the working group included -- expand the geographical definition of the border region to include another 200 km (124 miles) on the Mexico side; allow greater flexibility for using capital to fund projects aimed at minimizing pollution, and improving air quality; and recycling and reusing wastes, including efforts to certify and finance private sector environmental projects.

Conclusion
Admittedly, huge data gaps exist regarding water use, treatment and distribution in the border region as well as the extent of the point and non-point pollution sources. Monitoring data on health effects and treatment efficacy, when applied, are scarce from regions south of the border. History tells us, however, the need for basic hygiene, sanitation and water treatment transcends all boundaries. Taking a proactive stance to improve living conditions on a global scale is a primary defense against the spread of waterborne disease.

About the author
Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on development of rapid methods for detecting human pathogenic viruses in drinking water. She holds a master of science degree in public health (MSPH) from the University of South Florida and doctorate in microbiology from the University of Arizona. Reynolds also has been a member of the WC&P Technical Review Committee since 1997.