By Robin Mackar - NIH: A new study, supported by the National Toxicology Program (NTP), is the first to look at occupational exposure to bisphenol A (BPA) among manufacturing workers in the United States.
Researchers at the National Institute for Occupational Safety and Health (NIOSH) led the study, which appeared Jan. 1 in the journal Annals of Work Exposures and Health. NIOSH is one of the member agencies of NTP, and the study was conducted as part of an ongoing collaboration between the two agencies.
Manufacturing workers face higher BPA exposure
The researchers found that manufacturing workers exposed to BPA had levels of the chemical in their urine that were on average about 70 times higher than most adults in the U.S. population. Certain job categories were associated with average levels more than 300 times that of the general population.
The study did not evaluate the health of the workers involved. "Researchers studying health outcomes need exposure data, and published data on occupational exposures in the U.S. was very limited," said the paper's lead author Cynthia Hines, a senior research industrial hygienist with NIOSH. "Manufacturing workers may face the highest exposure levels of any worker group, so we concentrated on them, as an important first step."
Widespread exposure in general population
Researchers at the Centers for Disease Control and Prevention (CDC) have found BPA in the urine of nearly all people tested, indicating widespread exposure in the U.S. population. "Diet is thought to be the main nonoccupational source of BPA exposure," the authors wrote. However, according to CDC, finding a measurable amount of BPA in a person's urine does not necessarily mean it will result in a health effect.
Workers who participated in the new study handled raw BPA, often in large quantities. Unlike the general population, workers in the NIOSH study were exposed to BPA mainly by inhalation and absorption through the skin.
Learning more about occupational exposure
BPA is used to make polycarbonate plastics and some epoxy resins that are used to protectively line some food cans. In the past, BPA was used as a developer on thermal paper. BPA may also be added to certain specialty waxes that are used to make wax patterns for casting metal parts in manufacturing plants.
"We wanted to work with NIOSH to design a study that would allow a comparison with a similar study done in China," said John Bucher, Ph.D., NTP associate director. The new study found levels comparable to those reported in Chinese workers. Researchers in China linked exposures to effects on the male reproductive system (see citations below).
Study participants
The NIOSH study included six U.S. companies that made BPA, made resins with BPA, made wax with BPA, or used wax made with BPA. A total of 78 workers participated in the study, mostly white males. Over two days, participants provided seven urine samples. The participants also answered questions about food and beverage products they consumed in the past 24 hours.
NIOSH researchers found increased urinary BPA levels in workers who performed tasks such as handling sacks of BPA and taking process or bulk samples containing BPA for quality control testing. Among the highest exposed workers were those who worked with molten casting wax that contained BPA. The lowest urinary BPA levels were found in workers who handled a resin product with only trace levels of BPA.
Minimizing BPA exposure
Hines noted that although Europe places some limits on BPA levels in air, there are no occupational exposure limits for BPA in the U.S. Until research sheds more light on the potential for health effects among workers, Hines suggested that companies could take steps to minimize exposures. Such steps include trying to contain BPA dust and vapor emissions with local exhaust ventilation; cleaning surfaces in production areas, offices, and lunch rooms to remove BPA residues; and using appropriate personal protective equipment, such as respirators and gloves.
Companies and workers should also take steps to prevent exposures of family members to BPA residues on work apparel or other items workers may bring home. The NIOSH Science Blog provides more information about this study and ways to reduce exposure.
See full By Robin Mackar - NIH
