New Health Warning Issued for Lead, Benzene Exposure
Two new studies on the risks of human exposure to lead and benzene indicate that levels of the chemicals currently considered acceptable by authorities are too high and can result in serious health problems.
In the benzene study, researchers from the National Institute for Occupational Safety and Health (NIOSH) and the Centers for Disease Control reviewed the histories of more than 1,100 workers whose jobs at three Ohio rubber factories had exposed them to various levels of the chemical.
Benzene is a chemical solvent that is generally considered to be a human carcinogen. The workers in this study used benzene to dissolve rubber in the manufacture of a film called rubber hydrochloride.
The scientists found that workers who had been exposed to the daily level of benzene considered allowable by federal agencies ran a significant risk of developing leukemia. In addition, the researchers found that even those workers who had been exposed to a level one-tenth of the allowable level over a period of years ran a risk.
The researchers, headed by Robert A. Rinsky of NIOSH, concluded that any reduction in the permissible amount of benzene allowed in workplaces would result in a decrease in the number of benzene-caused leukemia cases. According to Rinsky, the study is the largest and most extensive yet on occupational exposure to airborne benzene.
In the report on lead, Harvard Medical School researchers led by David Bellinger measured the lead levels in newborn babies. The neurological and mental development of the infants then was tested every six months for two years. The researchers concluded that the development of infants appeared to be adversely affected even at levels of lead well below the limit considered safe by the Centers for Disease Control.
Bellinger said, however, that the findings need to be confirmed by additional studies and that it is unclear whether the low scores are an indication of a permanent effect on the children’s development.
The articles, which appear in the current issue of the New England Journal of Medicine, are accompanied by an editorial by Nicholas A. Ashford of the Massachusetts Institute of Technology calling upon federal regulatory agencies to review the present standards.
The new findings, Ashford said, “have implications for social policy regarding scientific evidence in future debates about the advisability of more stringently regulating exposure to asbestos, formaldehyde, dioxin and ethelene oxide, among other hazardous materials.”
The U.S. Occupational Safety and Health Administration (OSHA) sets daily and weekly limits on the amount of benzene that workers may be legally exposed to. The levels are based on previous studies of health risks associated with the chemical. That level currently is 10 parts per million parts of air per eight-hour day.
OSHA has set the occupational level for lead at 50 micrograms per cubic meter of air. For children, however, the Centers for Disease Control has considered the acceptable level to be no higher than 25 micrograms per deciliter of blood.
Reduce Standard
In 1978, OSHA reduced the occupational-exposure standard for benzene tenfold, from 10 parts per million in air for an eight-hour period to 1 part per million. That regulation was overturned in 1980 by a Supreme Court decision on grounds that the agency had failed to provide sufficient scientific evidence that 1 ppm is harmful. In his editorial, Ashford said the two studies “confirm the suspicion that very low levels of toxins are capable of causing serious health effects” and that they “should quiet the insistence that governmental efforts to control these hazards are excessive and irrational responses to chemophobia social forces.”
It is time, he said, “to re-examine whether scientific standards of proof of causality--and waiting for the bodies to fall--ought not give way to more preventive public health policies that are satisfied by more realistic conventions and that lead to action sooner.”
In their study of lead in babies, the Harvard scientists divided 249 newborns into three groups depending on the level of lead in their blood at birth--low, medium and high. After following the infants for two years and ruling out other possible reasons for below-normal mental development, the researchers found that the higher the blood lead level at birth the greater the chances of adverse development in motor skills and neurological ability.
This conclusion applied even to babies whose lead level was below the standard of 25 micrograms per deciliter currently in use. Unlike most previous studies, which have involved poor, minority children in inner cities, the Harvard babies were predominantly from white upper- and middle-class families whose lead level at birth had come from mothers who had not been exposed to lead at their work.
Detects Warning Sign
“It’s kind of a warning,” said Bellinger, a neurologist at Harvard. “What we’ve detected is a warning sign that we ought to be paying attention to prenatal exposure to lead.”
According to the Environmental Protection Agency, gasoline is by far the leading non-occupational source of lead, although paints once were a major source before that use was outlawed. Other current sources are drinking water that passes through lead pipes or that comes in contact with lead solder, and air pollution from the burning of coal or fuel oil.
