Hoá Chất Biosphenol A an toàn hay không?
Introduction
For the last 50 years, bisphenol A (BPA – CAS Nọ 80-05-7) is a
chemical used primarily to make polycarbonate plastic and epoxy resins.
Polycarbonate plastic possesses a unique balance of toughness, optical
clarity, high heat resistance, and excellent electrical resistance and has many
industrial uses including media products (eg., CDs, DVDs), electronic
equipments, sport equipments, bicycle helmets, food containers, drink
containers, baby bottles, medical devices and many other products. Epoxy
resins are commonly used to coat metal cans to protect the safety and
integrity of canned foods and beverages and also are used as dental sealants.
Exposure to BPA
Human exposure to BPA is via the use of plastic containers, bottles,
food and beverage cans and dental sealants. BPA has been found to leach
from bottle and can liners and migrates into foods and beverages.
Researchers from government agencies, academia, and industry worldwide
have studied the migration potential of BPA from polycarbonate products
into foods and beverages. These studies consistently show that the level of
BPA migrating into food is extremely low, generally less than 5 parts per
billion under conditions typical for uses of polycarbonate products.
Although BPA may be found in canned beverages and foods, it occurs only
at extremely low levels (generally less than 37 parts per billion).
Why BPA is of concern?
In recent years, a “low dose hypothesis” has been advanced claiming
that exposure to extremely low doses of certain substances could cause
adverse health effects in humans, including disruption of normal hormonal
functions. According to this "low dose hypothesis", reproductive and
developmental effects may result from exposure to low doses of BPA since
BPA was considered as having estrogenic activity in ovariectomized rats
(Dodds and Lawson, 1936). In 1970, Bitman and Cecil assayed DDT and 52
structurally related compounds (including BPA) in immature rats and the
authors reported an increase in uterine glycogen content. According to some
scientists, BPA thus mimics estrogen, a hormone that controls the
development of the brain, the reproductive system and many other systems
in the developing fetus and therefore BPA is an endocrineđisrupting
chemical and may harm the fetuses, infants, children or subsequently, adults.
What is an endocrine disrupting chemical?
Many chemicals are capable of disrupting the endocrine system of
animals including fish, wildlife, and human and are referred to as
endocrineđisrupting chemicals (EDCs). Indeed, our hormonal systems can
be disrupted by numerous different anthropogenic chemicals including anti-
androgens, androgens, estrogens, AhR agonists, steroid-hormone
antagonists, retinoid agonists, anti-thyroid substances, etc. Many of the
associations between EDCs and human health effects remain controversial,
but others, like the effects of diethylstilbestrol (DES), the androgenic drugs
danazol and methyltestosterone, and aminoglutethimide are widely
recognized. Recently, the increased availability of androgen products for
cutaneous application has increased the risk of virilization in children
through skin contact. Estrogen containing shampoos and skin oils were
shown to be causative factors for pseudo-precocious puberty in girls and
gynecomastia in boys. EDCs are not limited to pharmaceutical agents but
extend to industrial chemicals. In fact, the effects of PCBs (polychlorinated
biphenyls) on human neurological and immune development are well
known. Children exposed to PCBs in utero or in the early developmental
stages have lower birth weight, reduced IQ and cognitive abilities, reduced
sperm motility, and reduced in fertilizing capacitỵ Several phthalate esters,
used as plasticizers, are antiandrogens, which gives cause for concern.
Nowadays, US scientists also express concern about the potential role of
ECBs in increasing trends in obesity and type II diabetes noted in the general
population.
Is bisphenol-A an endocrineđisrupting chemical?
From previous investigations, BPA exhibits extremely weak hormonal
activity in in vitro assays and in laboratory animals at high doses. In more
recent years, extensive studies were conducted to determine if BPA could
cause reproductive or developmental adverse effects. In no study has BPA
been shown to be a reproductive or developmental toxicant. The “lowđose
hypothesis” for BPA has been thoroughly tested by numerous investigators
and agencies and the consistent lack of lowđose effects found in these
studies raise doubt about the validity of the “lowđose hypothesis”. Data from
the University of Arizona (Pritchett et al., 2002) indicated that, in humans,
BPA is rapidly metabolized to a hormonally-inactive form and excreted
rapidly from the bodỵ Collectively, the weight of evidence provided by these
studies demonstrates that BPA is not an endocrineđisrupting chemical and
there is no basis for human health concerns from exposure to low doses of
BPA.
Is bisphenol-A a carcinogen?
BPA is not a carcinogen. Based on lifetime exposure cancer bioassays
in laboratory animals, the US National Toxicology Program concluded that
BPA is not a carcinogen (NTP, 1982). The International Agency for
Research on Cancer (IARC) and the US EPA also conclude that BPA is not
a carcinogenic risk to humans (Haighton et al., 2002).
Bisphenol-A : Fear and perception
Depending on whom you talk to, BPA can be either a health risk or a
perfectly safe chemical. A number of concerned parents and adults believe
that exposure to BPA during pregnancy raises the risk of cancer and
childhood behavioral problems such as hyperactivity, AĐ, and autism. To
these individuals, BPA must be banned from the lining of milk bottles, can
foods and can beverages. On the other hand, the US FDA, the US EPA, the
United Kingdom Standards Agency, the European Scientific Committee on