Calafat, AM, Z Kuklenyik, JA Reidy, SP Caudill, J Ekong, LL Needham. 2005. Urinary Concentrations of Bisphenol A and 4-Nonylphenol in a Human Reference Population. Environmental Health Perspectives 113: 391-395.
Bisphenol A in the news
Background on BPA
Recent review of BPA
In the largest survey yet undertaken of human body burdens of bisphenol A and nonylphenol, scientists from the US Centers for Disease Control, found that 95% and 51% of Americans carry detectable levels of bisphenol A and nonylphenol. These concentrations are comparable to those reported in other studies.
For bisphenol A, the observed levels are clearly within the range of concentrations known to reliably cause adverse effects in laboratory experiments. The animal and cell studies link bisphenol A exposure to a wide range of health effects.
What did they do?
Calafat et al.measured bisphenol A (BPA) and nonylphenol (NP) in urine samples from a reference population of 394 adults. The samples were previously collected from approximately 1,000 adults (ages 20-59 years) as part of the Third National Health and Nutrition Examination Survey (NHANES III) callback cohort. This cohort was not chosen to be statistically representative of the United States and thus it is only generally indicative of nationwide patterns. Quality control samples were analyzed to assure the accuracy and reliability of the data. The samples were adjusted to take into account differences between samples in urine concentration/dilution.
For each sample, the researchers noted the participant’s age (50 years old or greater, or less than 50), sex, and residence (either urban or rural). This resulted in eight groups of samples:
- urban males > 50
- urban males < 50
- urban females > 50
- urban females < 50
- rural males > 50
- rural males < 50
- rural females > 50
- rural females < 50
From within these eight groups, 394 samples were randomly selected.
To improve the extent to which the results represent the U.S. population, the results from each of the eight groups were weighted by relating the sample size in each of the eight groups to the total number of people in the U.S. in each of those groups.
A statistically analysis was then conducted that took into account the degree of urine concentration, and considered the effects of age, sex, and urban/rural residence.
The results serve as reference ranges for the three population breakdowns (i.e., persons < 50 or ≥ 50 years of age; rural or urban residents; male or female).
What did they find?
BPA was detected in 95% of the samples, demonstrating that human exposure to BPA is almost universal. NP was detected in 51% of the samples.
The average level of BPA was 1.33 µg/L. Five percent of people sampled had levels in excess of 5.18 µg/L. These concentrations are equivalent to 1 to 5 parts per billion. Animal and cell experiments have reported adverse effects at equivalent doses, and below.
Urban residents had significantly lower levels than rural (p < 0.01). No sex or age differences were observed.
The median level of NP was <0.1 µg/L, except for males (0.17 µg/L), urban residents (0.11 µg/L), and people under 50 (0.11 µg/L). The 95 th percentile concentration of NP was 1.57 µg/L. There were not statistically significant differences in either the level of NP or the likelihood of detecting NP in urine by age, sex, or urban/rural residence, although the sample size was not large enough to conclude that no such differences exist.
What does it mean?
Despite widespread use of BPA and NP, little has been known about the extent of human exposure to these compounds. This study is the first to provide reference ranges for BPA and NP in the human body, from a diverse human population. It shows that nearly everyone has BPA in their body, despite the fact that BPA is quickly metabolized (within a day) by the body. This indicates that exposure to BPA is very frequent or nearly continuous.
The NP results are more ambigous because of the details of chemical analysis. The observation that only half the people sampled had detectable levels may reflect poor understanding of how NP is metabolized. Had a different metabolite been measured, it is possible that the researchers would have detected more widespread exposure to nonylphenol.
This study documents widespread and continuous exposure to BPA at levels comparable to and in some cases higher than those that cause adverse effects in animal studies and cell experiments. A recent review of the scientific literature indicates that BPA alters cellular signaling, fetal development, and adult physiology and reproduction in animals at doses within the range found in this survey, and far beneath the current 'safe exposure' level established by the US, 50 µg/kg (50 ppb). This reference dose is based on experiments conducted prior to 1988 indicating that BPA had no observable effect below 50 mg/kg (50 ppm). Indeed one recent study of BPA, examining calcium influx into cells, found effects of BPA at the parts per trillion (ppt) level. Calafat et al. with these new survey data demonstrate that people contain BPA in the parts per billion (ppb), 1,000 times higher than the lowest exposure at which an effect was seen on calcium influx.
The most important pathways for exposure to BPA and NP are not yet known, but both can be released into the environment during manufacture, or can be leached from food containers or other products during their use by consumers.
The levels of BPA observed in this study were comparable to the levels found in a Japanese study, and about seven times lower than in a group of 73 adult Koreans studied. The levels of NP found in this study are comparable to levels found in other studies.