Date Published: January 13, 2017
Publisher: Public Library of Science
Author(s): Xiaopeng Chen, Yanping Lin, Katherine Dang, Birgit Puschner, Hans-Joachim Lehmler.
We determined 12 polybrominated diphenyl ethers (PBDEs) and 19 polychlorinated biphenyls (PCBs) congeners in eight different brands of commercial whole milk (WM) and fat free milk (FFM) produced and distributed in California. Congeners were extracted using a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method, purified by gel permeation chromatography, and quantified using gas chromatography-triple quadruple mass spectrometry. PBDEs and PCBs were detected in all FFM and WM samples. The most prevalent PBDE congeners in WM were BDE-47 (geometric mean: 18.0 pg/mL, 0.51 ng/g lipid), BDE-99 (geometric mean: 9.9 pg/mL, 0.28 ng/g lipid), and BDE-49 (geometric mean: 6.0 pg/mL, 0.17 ng/g lipid). The dominant PCB congeners in WM were PCB-101(geometric mean: 23.6 pg/mL, 0.67 ng/g lipid), PCB-118 (geometric mean: 25.2 pg/mL, 0.72 ng/g lipid), and PCB-138 (geometric mean: 25.3 pg/mL, 0.72 ng/g lipid). The sum of all 19 PCB congeners in FFM and WM were several orders of magnitude below the U.S. FDA tolerance. The sum of PBDEs in milk samples suggest close proximity to industrial emissions, and confirm previous findings of elevated PBDE levels in California compared to other regions in the United States.
Dairy foods provide a variety of essential minerals, vitamins, and proteins known to be beneficial for health. However, exposure to potentially deleterious compounds through milk and dairy products must be considered as an important public health issue. Commercial cow milk is a source for exposure to polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). PCBs and PBDEs are two groups of contaminants of particular concern because both are endocrine disruptors and neurotoxicants that persist and bioaccumulate due to their inherent high lipophilicity (log Kow values range from 3 to 9). The chemical families of PBDEs and PCBs each consist of 209 congeners, many of which have been detected in human samples , raising concerns about their impacts on human health. Beginning in the 1920s PCBs were widely used as electrical insulators in transformers, capacitors, and heat exchangers, and as stabilizers in paints, plastics, and rubber products [2, 3]. PCBs were manufactured as mixtures of various congeners through progressive chlorination until a certain target percentage of chlorine by weight was achieved. In the U.S., these mixtures were referred to as Aroclors. The U.S. banned commercial PCB production in 1979. Major production of PBDEs began in the early 1970s for use as flame retardants in electronics, home furnishings, and foam products, including pet toys and bedding . PBDE mixtures were produced commercially at three different levels of bromination, leading to the terms penta-, octa- and deca-BDEs. BDE-99, BDE-47, BDE-100, BDE-153 and BDE-154 are most commonly added to polyurethane foam used for furniture cushions as commercial penta-BDEs mixtures. Octa-BDEs are used in the plastic housing for televisions, computers and other electronics, and are composed of 70–80% of hepta- and octa-BDEs. Deca-BDEs, mainly containing BDE-209, are also added to high-impact plastic housing for electronic equipment, plastic furniture and plastic toys.. In 2004, two commercial formulations, penta-BDE and octa-BDE, were banned or phased out of production in some U.S. states after a voluntary agreement between the U.S. EPA and the sole manufacturer of these products . California, who was the first state to phase out penta- and octa-BDEs, banned production, processing and distribution of products containing more than 10 percent penta- or octa-BDEs through California Assembly Bill 302, which became effective January 2008. The bill exempts deca-BDEs and does not require labeling of PBDE-containing products .
We found detectable levels of PCBs and PBDEs in all eight brands of commercially available bovine milk samples purchased in California with LODs ranging 0.3–5.8 pg/mL and 0.2–3.5 pg/mL for PCBs and PBDEs, respectively as listed in Tables 1 and 2. The targeted PCB and PBDE congeners’ detection frequency was above 50%. The sample preparation method produced recoveries for PCBs and PBDEs of 66%-116.8% and 66%-117.6% from fat free milk (FFM), and 74.3%-120.3%and 74.8%-117.7% from whole milk (WM), respectively (S3 Table). The lipid corrected concentrations of PBDEs and PCBs in FFM and WM are presented in Table 3. Due to low fat content, the lipid adjusted concentrations of PBDE and PCBs in FFM were much higher than those in WM.
In summary, contamination of bovine milk with PCBs and PBDEs is not unexpected and was confirmed in our study. The ∑PCBs in bovine milk samples were several orders of magnitude below the U.S. FDA tolerance for milk fat. Our findings provide further evidence for the importance of assessing non-legacy PCBs, such as PCB-11, in dietary sources. ∑PBDEs determined in our milk samples suggest the dynamic profile of PBDE concentrations based on geographic regions and calendar time. Finally, regular screening of dairy products is essential to assess the occurrence of contributions from dietary sources for environmental contaminant exposure.