2014/07/14

science 2.0
http://www.science20.com/steve_hentges/are_you_exposed_to_bpa_and_does_it_matter-140495

Are You Exposed To BPA, And Does It Matter?
Steve Hentges PC/BPA Global GroupFor quite a few years, one of the most popular chemicals for scientific inquiry has been bisphenol A(BPA). Scientists around the world have been conducting a diverse array of studies aimed atunderstanding whether BPA poses a risk to human health.

Based on the weight of evidence from these many studies, the U.S. Food and Drug Administration(FDA) recently answered the question “Is BPA safe?” with a simple and unambiguous answer - “Yes.”

By far, the majority of the studies conducted on BPA provide information on potential hazards, which
are intrinsic properties of the chemical. Since risk describes the probability that exposure to a hazard
will cause harm, information is also needed on human exposure to BPA.

Considering that BPA is a commonly used chemical, primarily as a raw material to make polycarbonate
plastic and epoxy resins, it is not surprising to find that people are exposed to BPA.
Of critical importance, though, is the magnitude of exposure. If there is no exposure, there can be norisk and, conversely, only when exposure is sufficiently high would risks potentially be present.

An increasingly accepted way to assess human exposure is through biomonitoring studies, whichmeasure the level of a chemical in biological samples such as urine or blood. For BPA, analyzing
urine is most appropriate since BPA is converted in the body to a biologically inactive metabolite andexcreted in urine within hours of exposure. Urine biomonitoring thus measures short-term exposure
to BPA over the last day or so.

When applied to a representative group of people, urine biomonitoring can provide a reasonablemeasure of average exposure to BPA across a population.

Recent U.S. and Canadian Data
Two recently published large-scale urine biomonitoring studies provide up-to-date exposure data forthe U.S. population (age 6 years and above) and Canadian pregnant women, respectively. The U.S.
data is from a long-standing program run by the Centers for Disease Control and Prevention (CDC)

and known as the National Health and Nutrition Examination Survey (NHANES).
The most recent data, from samples collected in 2011-2012, is contained in the fifth set of biennial
data over a 10-year period, which allows temporal exposure trends to be assessed.

The Canadian data is from the Maternal-Infant Research on Environmental Chemicals (MIREC) study,
which is sponsored by Health Canada and other Canadian government agencies. The study provides
exposure data for a large population ofwomenin the first trimester of pregnancy, with samples collectedin the 2008-2011 timeframe. The MIREC data is particularly valuable since pregnant women might
generally be considered to be one of the most vulnerable subpopulations.
＊MIREC : Maternal-Infant Research on Environmental Chemicals

The median and 95th percentile urinary BPA concentrations from both new studies are shown in thefigure below. Also shown for assessment of temporal trends are NHANES data from four earlier
biennial studies in the 2003-2010 timeframe.

A quick way to understand this type of data in a safety context is to compare the measured urinary
concentration values with a Biomonitoring Equivalent (BE) value.

A BE is defined as “theconcentration or range of concentrations of chemical in a biological medium (blood, urine, or othermedium) that is consistent with an existing health-based exposure guidance value such as a reference
dose (RfD) or tolerable daily intake (TDI).” Essentially a BE value is an estimated safe limit.

Several years ago, Health Canada sponsored a project to calculate a BE value for BPA inurine. Based on Health Canada’s TDI for BPA, the BE value was calculated as 1,000 micrograms/L,
which is shown as a bar across the top of the figure.

Casual inspection of the figure reveals that even 95th percentile urine concentrations of BPA are
approximately 2 orders of magnitude below the BE value. Typical human exposure, in the range ofthe median values, is hundreds of times below the BE value and Health Canada’s safe intakelimit. Although BE values are primarily useful as screening tools, the large margin of safety between
the BE value and the recent biomonitoring data clearly indicates that the U.S.population and pregnant
women in Canada are not at risk from real-lifeexposures to BPA.

Accordingly, in its announcement of the MIREC data, Health Canada stated “Based on the overall
weight of evidence, Health Canada continues to conclude that dietary exposure to BPA through foodpackaging is not expected to pose a health risk to the general population, including newborns andyoung children.”A second interesting feature in the figure is the apparent downward trend in exposure to BPA from2003-2004 to 2011-2012. The trend might best be described as suggestive since the decrease inurine concentrations is small and we cannot be certain whether the decrease is due to subtle changes
in the NHANES program (e.g., analytical methodology, participant selection, urine sampling) or is due
to decreased exposure in the US population.

Although biomonitoring data are a very useful measure of exposure levels, the data provide noinformation on sources of exposure, which makes it difficult to determine if the sources have changed
over time.

In spite of the clear statements of safety from government agencies such as FDA and Health Canada,
it would nevertheless not be surprising if some limited deselection of BPA has taken place in certainmarkets. In that case, it would be of particular interest to know what is being used to replace BPA.

That’s a fascinating subject, but one that will discussed another day in the near future.
Related Articles on Science 2.0
If You Are Scared Of BPA, JAMA Will Make You Happy
European Study Suggests Bottle-Fed Infants Most At Risk For Bisphenol A Ingestion, But Exposure
Levels Well Below 'Safe' Limits
Does Chemical X Cause Disease Y, And How Do We Know?
What Do We Really Know About BPA And Fertility?
The FDA On BPA Safety

PCMG