Prof. Dr. Aye Aye Khin, Head of the Department of Medical Laboratory Technology, University of Medic, Dr. Khin Chit, Deputy Director General, Department of Food and Drug Administration, Yangon, Win Pa Pa Soe, Laboratory Officer, Department of Food and Drug Administration, Yangon, Myanmar., Moe Moe Paing, Demonstrator, Department of Medical Laboratory Technology, University of Medical Tech
There are 7 types of plastics used in production of plastic bottles. According to their resin identification codes, they are as follow:
1 : Polyethylene terephthalate (PET)
2 : High-density polyethylene (HDPE)
3 : Polyvinyl chloride
4 : Low-density polyethylene, Linear low-density polyethylene
5 : Polypropylene
6 : Polystyrene
7 : Other plastics, such as acrylic, nylon, polycarbonate, and polylactic acid and multilayer combinations of different plastics (Plastic Packaging Resins, 2011) (What Do Recycling Symbols on Plastics Mean?, 2008).
Endocrine disrupting compounds (EDCs) such as bisphenol A, nonylphenol, tert-octylphenol, dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, butyl benzyl phthalate, di(2-ethylhexyl)phthalate and di(n-octyl)phthalate, can release in bottle water, especially, BPA can be detected at higher concentrations in polycarbonate containers (Amiridou & Voutsa, 2011). Bisphenol A which is released from polycarbonate drinking bottles mimics the neurotoxic actions of estrogen in developing cerebellar neurons (Le, Carlson, Chua, & Belcher, 2008).
In manufacturing of plastics, bisphenol A is used (Allard, 2014). Bisphenol A can be found in aquatic environment, air and soil (Kang, Kondo, & Katayama, 2006). It can also leach out from its containers and contaminate the contents of the containers, which are a source of human exposure to BPA (Rezg, El-Fazaa, Gharbi, & Mornagui, 2014). The daily intake of BPA in human should be less than 1μg/kg body weight/day (Kang, Kondo, & Katayama, 2006).
Polyethylene terephthalate (PET) bottles, which are assumed as BPA-free, are mostly used as containers in drinking water manufacturing in these days. But, one study proved that estrogenic chemicals often leach from BPA-free plastic products (Bittner, Yang, & Stoner, 2014). Moreover, Fan et al studied BPA from PET drinking water bottles of China in 2014. They found that BPA levels increased after one week storage, from 0.26 to 18.7 ng/L at 4۫C, from 0.62 to 22.6 ng/L at 25۫C, and from 2.89 to 38.9 ng/L at 70۫C (Fan et al., 2014). Also, in a study done in 2019, the results of BPA in recycled PET had the significantly higher levels (Dreolin, Aznar, Moret, & Nerin, 2019).
When BPA enters the blood, it can be detoxified by two mechanisms : glucuronidation and sulfation (Yokota et al, 1999). BPA is conjugated and excreted in urine (Thayer et al, 2015) (Völkel et al, 2002). However, due to the action of β-glucuronidase which is present in liver, kidney, intestine and placenta, BPA can deconjugate again in the blood (Ginsberg et al, 2009). Deconjugation of BPA can increase the BPA induced effects, mainly for the fetus, and moreover, the rate of glucuronidation in liver is slightly lower in pregnancy (Inoue et al, 2004).
BPA has been classified as a class 1B reproductive toxin by the European chemical classification and labeling (European legislation on chemicals, 2008), and class 2 B carcinogen by the International agency for research on cancers (IARC) (BPA Monograph, 2017).
BPA can associate with neurological disorders, can trigger pro-inflammatory pathway, can relate to breast cancer via post-translational modification process, can cause cell proliferation in ovarian cancer, can adduct DNA and induce DNA damage, can impair double strand break repair machinery of DNA, has catabolic effect on bone. High dose BPA is an endocrine disruptor (Jalal, Surendranath, Pathak, Yu, & Chung, 2018). There are also evidences in the relationships between exposure to BPA and chronic diseases, obesity, birth defects, developmental disorders, reproductive disorders and cancers (Rezg, El-Fazaa, Gharbi, & Mornagui, 2014).
Some of drinking water bottles in our country are labeled with resin identification code but some are not. The environmental temperature of our country is around 40۫C in hot season. Sometimes we unintentionally leave the plastic water bottles in high temperature, may be in households or in transportation of these bottles to the customers. And sometimes, we use water in these containers in cold temperature for a period of time. Our study is to find out whether these activities can affect the contamination of BPA in locally manufactured 1L plastic bottles drinking water.