A CRIS Bits research brief on the article, “Urinary Bispenal A (BPA) Concentrations among Workers in Industries that Manufacture and Use BPA in the USA” published in the Annals of Work Exposures and Health.
For most people, exposure to Bisphenol A (BPA) is relatively low, and primarily occurs from our diet (BPA is used in the packaging materials of some food and beverages). Thermal cash register receipts and some dental material are other sources of potential exposure.
But of course someone has to make the BPA and the BPA products that consumers use, and these workers face an entirely different kind of exposure than consumers do. Workers who make or use BPA may be exposed to higher concentrations of BPA and through a different route of exposure: by inhalation or by absorption through the skin.
There is currently no established occupational exposure limit for BPA. Before this study, we didn’t have data quantifying occupational BPA exposure to U.S. manufacturing workers. The National Institute for Occupational Safety and Health study is the first to measure BPA concentration in the urine of U.S. workers who make BPA or products containing BPA.
The study measured BPA in the urine of 77 workers from 6 different companies that manufactured BPA or used the substance to manufacture BPA-containing products. The majority of the workers were male (99%) and Caucasian (90%). The study measured two types of BPA:
- Free BPA is the chemical of concern and is known to have weak estrogenic effects. It is sometimes called unconjugated BPA or the “active” form of BPA.
- Conjugated BPA is the “neutralized” BPA. After ingestion the liver rapidly metabolizes Free BPA into Conjugated BPA. This form of BPA is not known to be harmful. It is sometimes called BPA glucuronide (BPA-G) or the “inactive” form of BPA.
- Total BPA is Free BPA plus Conjugated BPA.
The researchers measured Free BPA and Total BPA in the workers’ urine samples at 7 different time points across 2 consecutive work shifts. The first urine sample (Day 1 Pre-Shift) was taken before beginning the first shift and after being scheduled off work for 24 hours or more.
At Day 1 Pre-Shift, Total BPA was 20 times higher among the tested workers than in the general population. Across the 7 time points, Total BPA was about 70 times higher on average among the tested workers than in the general population. Total BPA concentrations increased over time – Total BPA was lowest at Day 1 Pre-shift and highest at Day 2 Post-Shift.
Free BPA was detected in 71% of all samples. The authors used the measured BPA in urine samples to estimate the amount of inhalation and dermal BPA exposure. These intake estimates indicated that a small number of the studied workers (1.4%) may have exceeded the US Environmental Protection Agency (EPA) oral Reference Dose for BPA1.
For consumers, our primary exposure concern with BPA is how much we ingest. But for people whose livelihood involves making BPA or BPA resins or waxes, exposure can occur in higher concentrations and also by inhalation or by absorption through the skin. It’s important to remember that workers in this study had repeated exposure through inhalation or dermal contact over months or years − a much different exposure in degree and kind than is the case for most consumers.
Workers had been off shift for an average of 70 hours before the first urine sample was collected. Given that BPA is thought to leave the body fairly rapidly, it was a concerning finding that Day 1 Pre-Shift Total BPA concentrations were 20 percent higher than the general population. The authors suggested possible reasons for the high baseline BPA concentrations, including “insufficient elimination time for some workers, a longer-than-expected elimination half-life, unaccounted for BPA exposure away from work, or BPA storage in the body.”
The fact that some workers may have exceeded EPA oral exposure limits raised important questions about occupational safety. Still, some cautions are in order. It’s difficult to determine an accurate exposure level based on urine samples, and the authors noted that differing estimation methods were used by the EPA, by the European Food Safety Authority (EFSA), and in their study. Moreover, comparisons to oral exposure limits may not apply to inhalation and dermal exposure.
The study didn’t directly assess health effects among the workers, and the authors concluded “The potential for BPA-related health effects among these workers is unknown”. However, they did note that BPA levels were similar to levels found in studies of BPA-exposed male Chinese workers – and those studies reported “changes in self-reported sexual dysfunction, reproductive hormone levels, and semen quality.” As such, the U.S. study also highlighted the need for ensuring appropriate protections are in place for U.S. workers.
Hines, C. J. et al. (2017). Urinary Bispenal A (BPA) Concentrations among Workers in Industries that Manufacture and Use BPA in the USA. Annals of Work Exposures and Health, 1-19. doi:10.1093/annweh/wxw021
1 The Day 1 intake estimate (based on the geometric mean) was 0.88 μg kg-1. For individual participants, the estimate ranged from a minimum of 0.035 to a maximum of 73.9 μg kg-1 BPA per day. The EPA oral Reference Dose for BPA is 50 μg kg-1 per day.
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