Preliminary environmental monitoring of water quality in the Rio Grande in the Laredo-Nuevo Laredo Region.

The international border region of the Rio Grande faces severe environmental and economic challenges. Contamination and degradation of its fragile lotic environments are mainly due to stresses from rapid population growth and unchecked industrial development. This study evaluates the water quality of the Rio Grande in the area of Nuevo Laredo, Mexico and Laredo, Texas, USA, in terms of physical, chemical and bacteriological parameters, as well as total metals, organochlorine pesticides, volatile organic compounds (VOC), semi-volatile organic compounds (SVOC) and radioactivity. Surface water samples were collected at 3 sites along the river. Two additional non-river sites (potable water and residual water) were studied for a better assessment of water quality in the region. Three series of samples were taken every other day during one week (November 3 to November 8, 2005) from the five sampling sites. Levels of oil and grease in all the river samples exceeded the limits established by Mexican regulations. Concentrations of aluminum above the permissible limits for source of drinking water and for quality for protection of freshwater biota were also found in all of the river sites. A number of unregulated elements (Cd, Sr, Mg, Na, Fe, Si, Li and K) appeared in the river samples. The average concentrations of Ba and Na in the potable water samples were below the permissible limits. Ca, Sr, Mg and Si were also found but are not regulated. The majority of the organic compounds studied in both the river and in residual water samples was below detection limits. In all the potable water samples, bromodichloromethane and dibromochloromethane were found above their limit of quantitation (LOQ), but these compounds are not regulated. This preliminary study suggests the need for consistent periodic monitoring to track the environmental status of the Rio Grande.