Paraquat poisoning from U.S.-supported marijuana eradication programs in other nations may threaten thousands of Americans with lung damage, a team of federal health officials has found.
The research disputes the State Department's finding last December that proposed aerial spraying of the herbicide in marijuana-producing countries would not endanger Americans who smoke the illegal plant.
Researchers at the Centers for Disease Control (CDC) estimated that, from 1975 to 1979, more than 9,000 Americans were exposed each year to paraquat in potentially toxic concentrations by smok- ing Mexican marijuana sprayed with paraquat.
Congress suspended support for the program in 1979. But the State Department wants to resume spraying and extend it to other nations, reportedly including Colombia and Jamaica.
If that happens, the scientists said, the risk of lung damage to smokers can be expected to increase.
In a report in the July issue of the American Journal of Public Health, the scientists warn that frequent exposure by marijuana smokers to the widely used weedkiller could lead to development of pulmonary fibrosis, a condition in which the lungs' delicate, oxygen-absorbing tissues become scarred.
"Our work shows that, if spraying programs begin again, there is a high likelihood of health risk to heavy smokers," said Dr. Philip Landrigan, chief of the surveillance and hazards division of the National Institute for Occupational Safety and Health, a CDC agency.
"Marijuana smoke, like tobacco, is toxic to the lungs," he said, "but chronic paraquat exposure would greatly increase the risk."
A State Department spokesman said studies had shown "no appreciable health risk from smoking marijuana sprayed with paraquat" and "no proven cases of paraquat-induced lung damage" resulting from the Mexican spraying program.
While Landrigan agreed no cases of paraquat poisoning among smokers had been reported, he said that "no systematic search was undertaken." He was critical of research the State Department used to determine health risks, which included a study conducted by the herbicide's principal manufacturer.
Government support for Mexican marijuana-eradication efforts averaged $30 million a year from 1975 to 1978. The sup port ended in April, 1979, after Joseph A. Califano Jr., President Carter's secretary of health, education and welfare, concluded that marijuana sprayed with paraquat "is likely to cause serious harm" to smokers.
Congress repealed restrictions on the paraquat program Dec. 15, 1981, but litigation delayed the Reagan administration's efforts to expand it. The government became legally free to resume support for Mexico's spraying program last December.
The CDC study also expressed concern about the possibility of toxic effects from dipyridyl, a residue produced when paraquat burns. The chemical causes bleeding in the lungs of test animals, according to Dr. Renata Kimbrough, a CDC toxicologist.
A companion program to spray poppies in Mexico was "highly successful," the CDC researchers noted, resulting in a sharp decline in heroin importation and "reduction in the number of reported deaths in the U.S. due to heroin overdose from 1,770 in 1976 to 540 in 1977."