Factory workers who are routinely exposed to lead on the job show increased signs of impaired thinking, reduced manual dexterity and diminished muscle strength compared to workers who are not exposed to lead at work.
These are the findings of a new study conducted by researchers at the Johns Hopkins School of Public Health, who also found that workers with higher levels of lead in their blood evidenced reduced neurobehavioral function.
The study was conducted with factory workers in South Korea, but the findings suggest that safety standards for workers exposed to lead in the United States and other nations may need to be modified. The study appears in the March issue of the American Journal of Epidemiology.
"We found some workers with diminished cognitive abilities with blood lead levels of as low as 15 to 20 micrograms per deciliter," says lead author Brian Schwartz, M.D., M.S., associate professor of environmental health science at the Johns Hopkins School of Public Health. "The current safety standard for lead exposure in the U.S. is a blood level of 40 to 60 micrograms per deciliter, which may be too high," adds Dr. Schwartz.
For the study, the researchers examined 800 factory workers in South Korea who were routinely exposed to lead while manufacturing car batteries. The investigators compared these workers with 135 factory workers from other industries who were not exposed to lead at work.
The research team estimated the amount of lead in the blood, bone and tissue of the participating workers. The workers were then given the World Health Organization Neurobehavioral Core Test Battery, which is a set of eight standardized tests that measure memory, problem solving and other central nervous system functions. Several additional tests were given to measure manual dexterity, motor skills and muscle strength.
After adjusting for differences in age, height and weight, educational background and gender among the workers, the researchers found that workers with higher levels of lead in the blood scored lower on nearly all of the tests measuring executive function and reasoning when compared to the workers who were not exposed to lead.
Workers exposed to lead also scored lower on tests measuring dexterity, coordination and muscle strength when compared to the workers from the control group who were not exposed to lead.
"We found that blood lead level was the best indicator of poor performance on the neurobehavioral tests. We believe that in workers currently exposed to lead, the short term effects of lead on test scores, as best assessed by blood lead levels, may outweigh any possible long term effects of lead, as assessed by lead in bone.
"The correlation between poor test scores and measurements of lead in the bones and tissue was not as strong," explains Dr. Schwartz. However, the researchers believe that bone lead levels may be a better indicator of decline in test scores over time.
Lead may have both short term and possibly reversible effects, as well as long term and probably irreversible effects on central nervous system function. Information on the influence of lead on neurobehavioral test scores over time should be available within the next year.
The study was funded by a grant from the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health.