17.
Transboundary Exposures
Authors
The information in this chapter was prepared by Tim Flood, M.D., Medical Director, Chronic Disease Epidemiology Section, Arizona Department of Health.
United States - Mexico Pollution
Since the U.S. and Mexico share a common border, it is not surprising that environmental problems could affect the inhabitants of either side of this political border.
The larger U.S.-Mexico cities include: Douglas-Agua Prieta; Nogales-Nogales; San Luis-San Luis (near Yuma).
The three media that the Committee considered are air, water, and soil.
Nogales
Water
Nogales Wash runs in a northern direction as an open drainage ditch from the Mexican side, through the town of Nogales, Arizona, and joins the wastewater treatment plant north of town. Contaminants detected in the wash include petroleum chemicals, metals, and coliform bacteria including cholera and viruses.
Currently, only very few persons are believed to be exposed to these contaminated water bodies because:
o The municipal water supply comes from a separate aquifer.
o The surface water in the wash is not used as a drinking water source.
The water underneath Nogales, Arizona contains measurable levels of trichloroethylene (TCE) and other chlorinated chemicals. It is possible that some private wells have tapped into a plume of tainted water. Few, however, if any, persons in the Nogales area are known to be drinking any water (private or public) that exceeds the EPA standards.
Air
There are several hazards along the border. All cities are exposed to vehicular traffic and the associated exhaust fumes. Additionally, Nogales, Arizona residents are exposed to:
o Smoke from a burning municipal dump
o Chemicals released from maquiladores
o Dust smaller than 10 microns
o Lead present in gasoline sold in Mexico
o Illegal burning
The measured levels of air contaminants in Nogales appear to be similar to the levels measured in metropolitan Phoenix.
Soil
At present there are no known major sources of contaminated soil that threaten human health.
Existing Health Data for Nogales
The overall mortality pattern in Nogales is similar to that of other Arizona counties (ADHS, 1990). Currently, the ADHS and the University of Arizona are studying a reported excess of multiple myeloma and lupus cases in Nogales.
The Committee does not include here the increased risk for infectious diseases due to environmental contamination or inadequate immunization of U.S. residents.
If the myeloma cases are confirmed and an environmental link is established, then the magnitude of the risk might be about three excess myeloma cases per year and one to three excess lupus cases per year. Data are inadequate to make a statement about other chronic diseases.
Douglas and San Luis
Health patterns are not believed to be different than those found in other Arizona cities. There are no known environmentally-associated diseases.