Migration of Bisphenol A (BPA) in Baby Milk Bottles
Sun, C.L.
Department of Chemistry, Faculty of Science,National University of Singapore
3 Science Drive, Singapore 117543
ABSTRACT
Bisphenol A- an endocrine disruptor, is the monomer used for the manufacture of polycarbonate plastics
widely used in baby milk bottles and other food packaging materials. Previous studies have shown that BPA
may migrate into the food at elevated temperatures. In this study, migration tests in both oil and 10% ethanol
for all twenty-six baby milk bottle samples were performed at elevated temperatures, and High Performance
Liquid Chromatography (HPLC) analysis was done on the test solutions for their leachable BPA levels after
8, 72 and 240 hours. The amount of BPA migration in oil ranged from N.D. to 0.37 mg/inch2, while BPA
migration in 10% ethanol ranged from N.D. to 1.92 mg/inch2.
INTRODUCTION
Bisphenol A ( 4,4-isopropylidene diphenol, CAS Registry No. 80-05-7, more commonly known as BPA) is
one of the reactants used in the manufacture of polycarbonate (PC) plastics. These plastics are produced by the
condensation of BPA with carbonyl chloride.
Polycarbonate plastics are used in food packaging containers such as baby milk bottles because of their
toughness and durability, as well as their good physical stability at elevated temperatures.
However, it may be possible that at elevated temperatures, hydrolysis of the polycarbonate plastic could result
in the trace formation of BPA monomer at the plastic surface, consequently migrating into the food it comes
into contact with. Since PC plastics are used widely in baby milk bottles, the migration of BPA from the milk
bottles into the baby milk that children drink is of particular concern to us. Hence, the aim of this study is to
investigate the presence and quantity of BPA leached out from the PC plastic baby bottles by simulating
normal, repeated use conditions.
Health Effects of BPA
BPA belongs to a group of chemicals known as endocrine disruptors that mimic or block the actions of our
natural hormones, especially oestrogen. Hormones are involved in just about every biological process: immune
function, reproduction, growth, and even controlling other hormones in the body. They work at incredibly
small concentrations, in ppb, or ppt, which is why small doses of endocrine disrupters could be dangerous.
Recent studies have shown that at very low doses of 6µg/L, BPA can exhibit xenoestrogenic effects in vitro
(1). BPA has been linked to reduced sperm production, increased prostate weight, and testicular cancer among
males. In females, conditions such as endometriosis may occur - the abnormal growth of endometrial cells
outside the uterus that may cause infertility. Since xenoestrogens mimic naturally occurring oestrogen, they
may also cause the breast cancer cells to proliferate, increasing the risk of breast cancer. BPA may also affect
the onset of puberty in humans and in the offspring of some mammals. Children, especially unborn and
newborn babies, are at the greatest risk from such chemicals because imbalances of hormones can have
pronounced effects during their critical developmental stages, although many of which do not reveal
themselves until much later in life.
The current EU migration limit of BPA is set at 3 milligrams per kilogram (ppm) of food.
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Method of Investigation
Twenty-seven brands of baby bottle samples were brought in from the Food Control Department (FCD) to be
tested for their levels of BPA residue and migration. These twenty-seven baby bottle samples were analysed by
Fourier Transform Infrared Spectroscopy (FT-IR) method to determine the composition of the plastic material
used. Of these twenty-seven baby bottles, twenty-six of them were found to be made of polycarbonate resin,
thus were further tested for their BPA residue and migration levels. The remaining baby bottle (SW0012) was
found to be made of polypropylene, therefore no further tests were carried out for this sample.
We performed a 10-day test for the baby milk bottle samples in oil at 100°C, and in 10% ethanol at 70°C based
on the test recommendations by the US Food and Drug Administration (FDA) for articles intended for repeated
use. These migration-testing protocols were intended to simulate the most anticipated end-use conditions of the
baby milk bottles and were based on the premise that additive migration to aqueous and fatty- based foods was
typically diffusion-controlled within the polymer. Since milk is both aqueous and oily, we performed the
migration tests with different test solutions to simulate milk in the baby milk bottles for BPA migration- corn
oil, and 10% ethanol solution. The test solutions from the migration experiments were analysed after 8 hrs, 72
hrs, and 240 hrs by High Performance Liquid Chromatography (HPLC).
EXPERIMENTAL PROCEDURES
Reagents:
Bisphenol A (minimum purity 99%) was obtained from TCI, Tokyo KASEI. HPLC grade n-hexane, methanol,
and acetonitrile were obtained from Lab-scan Analytical Sciences. Trifluroacetic acid (TFA) was obtained
from Merck (Sehuchardt). A standard solution containing 375ppm of BPA and a substock containing 37.5ppm
of BPA were prepared in methanol and kept in the refrigerator. Solutions of the required concentrations were
prepared daily by dilution.
Instruments:
The HPLC analysis was performed using a Jasco HPLC system equipped with a Jasco PU-1580 Pump, Jasco
AS-1550 Intelligent Autosampler, and a FP-1520 Fluorescence Detector. A mechanical shaker (Vortex) was
used to homogenise the standards and samples prior to the use of HPLC.
Preparation of Oil Samples
A 1-inch thick strip of the baby bottle sample of known surface area was placed into glass beakers filled with
corn oil of ratio 10 mL/inch2, then placed into the oven at 100°C for 10 days. At 8hrs, 72hrs, and 240hrs,
portions of the test solutions from the migration experiment were taken out to be analysed as follows.
i)
1 ± 0.01 g of the oil samples were weighed into clean test-tubes.
ii)
3.0mL of n-hexane was added to dissolve the oil samples, followed by 2.0mL of methanol/water (1:1).
The mixtures were shaken for 2 minutes, and allowed to stand for 30 minutes for separation.
iii)
The lower aqueous layer of each sample was extracted using a dropper, and transferred to HPLC vials
for HPLC injections.
Preparation of 10% Ethanol Samples
Another 1-inch thick strip (of known surface area) was cut out from each sample, placed into glass jars filled
with 10% ethanol (v/v) of ratio 10 mL/inch2, then placed into the oven at 70 °C for 10 days. At 8hrs, 72hrs, and
240hrs, 1mL of the test solutions from the migration experiment were transferred into HPLC vials to be
analysed.
HPLC OPERATING CONDITIONS
A Jasco HPLC system with a reversed phase column was used with fluorescence detection.
Pump Mode: 1 Pump Isocratic Mode; Flow rate: 1.000ml/min; Gain: 100
Min. Pressure: 0.0 MPa; Max. Pressure: 40.0 MPa; Temperature: 35.0 °C; Run length: 10 minutes; Injection
Vol: 20 µL. Excitation wavelength: 235 µm , Emission wavelength : 317 µm
Column: Hypersil HyPURITY Elite C18 5µm 250 x 4.6mm;
Mobile phase: 65% Acetonitrile with 0.1% TFA
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RESULTS AND DISCUSSION
A. Determination of BPA residues in Milk Bottle Samples.
Sample
Content of
BPA /ppm
17.23
15.20
SW0001
SW0002
SW0003
SW0004
SW0005
SW0006
SW0007
N.D.
N.D.
9.61
N.D.
10.53
Sample
Content of
BPA /ppm
Sample
SW0008
SW0009
SW0010
SW0011
SW0013
SW0014
SW0015
N.D.
SW0016
SW0017
SW0018
SW0021
SW0022
SW0023
5.87
N.D.
28.06
25.80
61.64
4.01
Content of
BPA /ppm
7.53
44.40
6.60
29.70
17.12
N.D.
Sample
SW0024
SW0025
SW0026
SW0027
SW0029
SW0034
Content of
BPA /ppm
31.40
41.50
8.10
N.D.
28.40
141.00
(Limit of Detection = 3ppm)
B. Determination of BPA Migration in Samples
Fig. B-1
Chromatogram of blank sample.
Fig B-2
Chromatogram of Standard 3
Fig B-3
Chromatogram of Sample SW0008
• Retention time of methanol is between 2-4
minute.
• Retention time of BPA is at 4.00min.
• BPA was found to be at a level of
0.071ppm after 72 hours by integrating
the peak area.
C. Results of BPA Migration in Both Oil and 10% Ethanol
BPA Migration in Oil
Content (mg per sq. inch)
0.8
8hrs
72 hrs
240 hrs
0.7
0.6
0.5
0.4
0.3
0.2
0.1
SW
00
SW 02
00
SW 03
00
SW 04
00
SW 05
00
SW 06
00
SW 07
00
SW 08
00
SW 09
00
SW 10
00
SW 11
00
SW 13
00
SW 14
00
SW 15
00
SW 16
00
SW 17
00
SW 18
00
SW 21
00
SW 22
00
SW 23
00
SW 24
00
SW 25
00
SW 26
00
SW 27
00
SW 29
00
34
0
samples
3
BPA Migration in 10% Ethanol
Content (mg per sq. inch)
2.5
8hrs
72 hrs
240 hrs
2
1.5
1
0.5
Limit of Detection
= 0.045ppm
SW
samples
00
SW 01
00
SW 02
00
SW 03
00
SW 04
00
SW 05
00
SW 06
00
SW 07
00
SW 08
00
SW 09
00
SW 10
00
SW 11
00
SW 13
00
SW 14
00
SW 15
00
SW 16
00
SW 17
00
SW 18
00
SW 21
00
SW 22
00
SW 23
00
SW 24
00
SW 25
00
SW 26
00
SW 27
00
SW 29
00
34
0
Diagram C.
Migration results
in both oil and
10% Ethanol
over 10 days.
The BPA residue levels determined in the different samples ranged from 0 ppm to 141ppm. This could be
due to the different sources of raw materials used and the different processing conditions. There was no direct
correlation between the level of BPA residues in the samples and their corresponding migration to the foodsimulating liquids, implying that high levels of residues remaining in the baby bottle strip do not necessarily
bring about high migration of BPA into the surrounding liquid, vice versa. A possibility for this non-linear
relationship could be due to the hydrolysis of BPA at the plastic surface, consequently migrating into the
liquid.
BPA migration in oil ranged from N.D. to 0.37 mg/inch2 in 10 days, while the migration in 10% ethanol
ranged from N.D. to 1.92 mg/inch2in 10 days. Duplicates were done in order to ensure the accuracy and
reproducibility of the results. Recognising that calibration of the working standards was important for accurate
determination of the analyte in samples, care was taken to ensure that the calibration curve had a correlation as
close to 1 as possible, points lied close to the curve, and its best fit straight line cut the axis as close to the
Origin as possible. The calibration curve was obtained by plotting the areas of the standard versus the absolute
amounts. (Refer to Appendix B-1, B-2, B-3 attached) A blank sample was prepared to confirm the presence of
the BPA in the chromatograms and identify the presence of interferences. BPA in the samples were identified
by comparing its liquid chromatography retention time with that of the authentic BPA.
From the results, BPA migration was greater in 10% ethanol than in oil. Due to the nature of milk, which is
both aqueous and slightly oily, the combined effect of BPA migration in milk may be even higher than the
values found in pure oil and ethanol.
CONCLUSION
The results showed that BPA did migrate into the surrounding food-simulating liquids in varying amounts,
implying that children have been exposed to this monomer since birth. Due to the xenoestrogenic nature of
BPA and its likely consequences, it brings about a cause for concern, especially when the blood-brain barrier
of newborns and infants have not been fully developed yet, hence, are very susceptible to chemicals. By
converting the values (in mg/inch2) into the actual baby milk bottles’ dimensions, the leachable BPA levels of
some samples have exceeded the 3ppm approved limit set by the EU. Therefore, this brings about a cause for
concern even though other brands exhibit undetectable leachable BPA levels. Precautionary measures such as
regular checks and more stringent control are necessary to ensure the safety of the public.
ACKNOWLEDGEMENT
I sincerely thank Dr. Loke Swee Leng and Mdm Yap Wee Kim of the Centre for Analytical Science, Health
Sciences Authority for their support and valuable guidance throughout.
REFERENCES
1. Krishnan, A. V., Stathis, P., Permuth, S. F., Tokes, L., and Feldman, D., 1993, Bisphenol A: An
Oestrogenic Substance is Released from Polycarbonate flasks during Autoclaving. Endocrinology, 132,
2279-2286.
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2. J.E. Biles, *T.P. McNeal, T.H. Begley, and H. C. Hollifield., 1997, Determination of Bisphenol A in
Reusable Polycarbonate ood-Contact Plastics and Migration to Food-Simulating Liquids. J. Agric. Food
Chem, 45, 3541-3544
3. http://www.cfsan.fda.gov/~dms/opa-cg5a.html
4. http://www.cfsan.fda.gov/~dms/opa-cg5.html
5. http://website.lineone.net/~mwarhurst/complexity.html
6. http://website.lineone.net/~mwarhurst/bisphenol.html
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