LEBANON, N.H. -- Dartmouth Medical School (DMS) researchers have discovered industrial pollution sites in northern Mexico that have higher than ever before reported levels of heavy metal contamination. Smelters in Torreón and Chihuahua constitute a serious environmental threat to people living near these industries, according to a report in the April issue of Environmental Health Perspectives, the monthly journal of the National Institute of Environmental Health Sciences.
"This is one of the most heavily contaminated residential areas in the Western Hemisphere and it has never been studied," says James Sargent, MD, a principal author of the study, and a pediatrician at Children's Hospital at Dartmouth at Dartmouth-Hitchcock Medical Center and Dartmouth Medical School.
In July 1995, roadside dust samples were collected from residential areas within 2,500 meters of smelters and refineries located in the cities of Torreón, Monterrey, and Chihuahua. Smelters and refineries are known to be potential sources of heavy metal contamination such as arsenic, cadmium, and lead. These cities have dry, dusty climates with residential areas lacking any substantial ground cover such as grass or bushes. Without adequate ground cover, heavy metal pollutant-laden dust is more ubiquitous and airborne, increasing the likelihood that it will be ingested or inhaled.
In all three cities, heavy metal concentrations exceeded maximum acceptable levels established by the EPA for cleanup at U.S. Superfund sites. "Previous studies of heavy metal exposure in Mexico have focused primarily on lead in gasoline and household ceramics," said Sargent. "Other environmental contaminants such as cadmium and arsenic have largely been ignored."
Based on data from previous studies, Sargent estimates the average blood lead levels in children living within 1 mile of the Torreón smelter would be approximately 40 mcg/dL. "Anything over 20 mcg/dL is harmful to children," he said. For infants and young children, lead exposure has been shown to decrease intelligence (IQ) scores, slow their growth, and cause hearing problems. Exposure to high lead levels can badly damage the brain and kidneys of adults and children.
Sargent also fears that the levels of cadmium and arsenic exposure are higher than what's safe. "The cadmium levels in Torreón are higher than have ever been reported at industrial sites," he says. "Cadmium causes permanent damage to your kidneys and it is not easily excreted from the body." Cadmium also causes lung damage such as emphysema, as well as hypertension and osteoporosis. A suspected carcinogen, Cadmium increases the risk of lung cancer and prostate cancer.
Arsenic causes neurological and liver damage and has been shown to cause skin cancer. Inhaled arsenic can increase the risk of lung cancer -- this has been observed in humans exposed to high levels of airborne arsenic in or around smelters.
"We are very concerned by the levels of contamination in these areas, especially because the smelters are surrounded by residential neighborhoods," said Madeline Dalton, PhD, another DMS researcher on the study. "It suggests that these industries have not been adequately monitored for environmental safety. Clearly, further investigation is warranted."
The smelter in Torreón, a manufacturing and mining center with a population of about 500,000 people, is the largest nonferrous metallurgical complex in Latin America and the fourth largest in the world. The smelter in Chihauhua, historically a prosperous mining center, has been inactive since 1990. Samples from Monterrey were collected near an active lead crystal factory and an inactive lead refinery. Monterrey, a city of 3 million people, is a commercial capital in northern Mexico.
Other study authors include DMS researcher and pediatrician, Andrea Benin, MD, and Sandy Roda, MS, Kettering Laboratory, Department of Environmental Health, University of Cincinnati. The study was supported by an American Academy of Pediatrics resident research grant and a Helen's Fund grant from the Department of Pediatrics, Dartmouth-Hitchcock Medical Center.