Bisphenol A is a carbon containing synthetic compound employed to make certain plastics and epoxy resins. It exhibits some similarity with animal hormone. In present day society we are largely exposed to bisphenol A by different direct and indirect ways. Widespread exposure to bisphenol A may even cause cancer. Various uses and alerts for such uses are discussed in a nut shell in this article.
Are you habituated with keeping the mini statements of bank ATMs or the meter reading cum electricity bills alike? Do you retain the bills of shopping malls or petrol pumps regularly? If yes, then it needs your urgent attention. Researchers have revealed that the chemicals used for making those bills and statements can invite cancer and other lethal diseases to our body. Though it sounds unnatural to ordinary ears, bisphenol A used mainly in making of polycarbonate plastics, epoxy resins and thermal papers as in those bills and statements, is basically a carsinogen, i.e., substance responsible for cancer. Unfortunately the deadly presence of bisphenol A in many articles used in modern life has become evident. It may be used in some food and drink packaging, in making polycarbonate bottles for carrying water or feeding bottles for infants as well as plastic utensils used with microwave oven, bisphenol A leaves nothing beyond its range, so far as its indiscriminate use is concerned.
What is bisphenol A?
Bisphenol A (BPA) is a carbon based hydroxyphenol compound with the chemical formula (CH3)2C(C6H4OH)2 belonging to the group of diphenylmethane derivatives. It is a colourless amorphous solid that is soluble in organic solvents, but poorly soluble in water.
Bisphenol A was first synthesized from the condensation of acetone with two equivalents of phenol by the Russian chemist A P Dianin in 1891. The suffix ‘A’ in the name of the compound designates its origin from acetone. The reaction was catalyzed by either hydrochloric acid or a sulphonated polystyrene resin. However, commercially BPA is extracted from many resinous byproducts under high vacuum or solvent-based extraction using additional phenol followed by distillation.
Bisphenol A is used primarily to make plastics, and products using BPA-based plastics have been in commercial use since 1957. At present at least 3.6 million tonnes of BPA are used yearly by manufacturers in the world. It is a key monomer in production of epoxy resins and in the most common form of polycarbonate plastics. BPA based polycarbonate plastics are clear and tough, and are made into a variety of common consumer goods, such as water and infant feeding bottles, compact discs and digital versatile discs, impact-resistant safety equipments, eyeglass lenses, sports equipments, household electronic gadgets, foundry casting and medical devices (Figure 1). Some dental fillings sealants and composites may also contain BPA. Epoxy resins are used as lacquers to coat metal products such as food and beverage cans, bottle tops, and to line water supply pipes. BPA is used as a preferred colour developer in making carbonless copy paper and thermal paper such as used in sales receipts and ATM statements (Figure 2).
Moreover, BPA is used in the synthesis of some thermoplastic polymers such as polysulfones and polyether ketones, which are applied as antioxidant in some plasticizers. Bisphenol A is applied as a polymerization inhibitor during the manufacture of polyvinyl chloride (PVC). BPA is also used in commercial production of the flame retardant chemical tetrabromobisphenol A, and previously was used as a fungicide.
BPA exposures to human body
The major source of human exposure to BPA is through the diet while air, dust and water are other possible sources of exposure. Bisphenol A is leached from some consumer products such as polycarbonate tableware, food storage containers, water bottles, and baby bottles and from the lining of food and beverage cans (Figure 3) where it is used as an ingredient in the plastic used to protect the food from direct contact with the can. The degree to which BPA leaches from polycarbonate bottles into liquid may depend more on when they are cleaned with harsh detergents or they contain acidic or high-temperature liquids, than the age of the container. Plastics containing BPA are used to make some microwavable utensils. In high temperature, inside the oven, BPA breaks down and leaches into the cooked food. BPA is used to form epoxy resin coating of water pipes; such resin coatings are used to avoid replacement of deteriorating pipes. Leaching may occur from such water pipes to potable water.
There is limited evidence on inhalation exposure but dermal absorption continues to grow. BPA can penetrate our skin. In a tropical country like India, this possibility goes up to ten times higher than the usual rate. According to the experts, if a person makes use of thermal paper or carbonless copy paper for a long stretch of time, then BPA easily goes into the skin and get mixed with the blood. Moreover, in thermal papers free or non-polymerized BPA are used instead of polymerized BPA as used in epoxy resins or polycarbonate plastics. This non polymerized form of BPA is more exposable than the polymerized form.
However, in many cases such as adhesives, automobiles, digital media, electrical and electronic gadgets, sports safety equipment, electrical laminates for printed circuit boards, composites, and in paints, potential exposures of BPA have not been fully assessed still now.
Target age groups and BPA
Children may be more susceptible to BPA exposure than adults. A study found higher concentrations of BPA in urinary discharge in young children than in adults under typical exposure scenario. In adults, BPA is eliminated from the body through a detoxification process in the liver. In infants and children, this pathway is not fully developed so they have a decreased ability to clear BPA from their system. Bisphenol A is hazardous to fetuses, infants, and young children. Infants fed with BPA lined tin packed baby foods or liquid formulae fed from polycarbonate baby bottles (Figure 4) are among the most exposed. Exposure can also occur in infants and young children through accidental ingestion by chewing on certain plastic baby books or toys.
Researches have revealed that BPA can be found in both the placenta and the amniotic fluid of pregnant women. So when a pregnant woman is exposed, thereby the fetus has the possibility of BPA exposure. Surprisingly, BPA can be found in breast milk also.
In country like India, teenagers are largely exposed to bisphenol A. Today’s shopping mall culture as well as the habit of consuming canned food and beverages play prominent role of exposure for the teens (Figure 5). The other target group of BPA exposure is the adults. In adults the major route to BPA is diet. Besides diet, exposure can also occur through air and through skin absorption mainly comes from handling receipts. Further, it has been demonstrated that thermal receipts placed in contact with paper currency in a wallet for 24 hours cause a dramatic increase in the concentration of BPA in paper currency, making paper money a secondary source of exposure.
Effects on human health
Bisphenol A was first recognized to have a role similar to synthetic estrogen in 1936 long before it was used to form polycarbonate plastic and resins in the early 1950s. BPA’s ability to mimic the effects of natural estrogen (like estradiol or E2) derives from the similarity of phenol groups on both BPA and estradiol. Long term BPA exposure has been associated with reproductive problems in both wildlife and humans. Studies have shown a decline in human sperm count and quality, genital abnormalities such as abnormal penile or urethra development in males, early onset of puberty in females, effects on fertility, miscarriage and birth defects.
Bisphenol A is a carcinogen and its deposition to human body boosts the risk of causing breast and prostate cancer. Moreover, exposure to BPA increases the possibility of brain tumour or meningioma. BPA is a thyroid-disrupting chemical, which may especially affect pregnant women, neonates and small children. Recent research states that bisphenol A is responsible for malfunction of cell organelle centrosome. BPA is also associated (Figure 6) with increasing neurobehavioral problems, increasing prevalence of obesity and type2 diabetes, and immune system effects.
Obesity as well as gaining extra weights due to BPA exposure may give rise to certain secondary complications to our body such as sleep apnea, abnormal lipid profile, high blood pressure, stroke, pulmonary blood clot, asthma, pancreatitis, liver cirrhosis, colon cancer, arthritis, and gout.
Scientists now believe that there are at least two mechanisms by which BPA disrupts normal body function in human. The endocrine system is the chemical communication system found in humans. The endocrine system typically handles long term functions and processes, including the development of the brain, nervous system, and other organs and tissues, growth and metabolism, and the functioning of the reproductive system. Hormones are the chemical messengers of the endocrine system. The nervous system, on the other hand, is the rapid communication system controlling functions such as heartbeat, breathing, and movement. BPA can act as a potent estrogen, binding to the estrogen receptor. Alternatively, BPA can block the effect of stronger natural estrogens, inhibiting estrogen function. They are commonly assumed to act through the estrogen receptors in the cell nucleus that regulate cell signaling and influences gene expression. In addition, bisphenol A produces changes in DNA structure by adding methyl groups to DNA, silencing their expression.
Precisely to say, bisphenol A leaves its impact both on humans and environment. BPA can enter the environment either directly from chemical, plastics, coat and staining manufacturers, from paper or material recycling companies, foundries who use bisphenol A in casting sand, or indirectly leaching from plastic, paper and metal waste in landfills or ocean-borne plastic trash. Ubiquity makes BPA an important soil pollutant.
BPA can currently be found also in municipal waste water. It affects growth and development in aquatic organisms. Among freshwater organisms, fish appear to be the most sensitive species followed by aquatic invertebrates, amphibians, and reptiles. In addition, BPA affects reproduction in aquatic and terrestrial annelids, molluscs, insects, crustaceans, fish and amphibians; impairs development in crustaceans and amphibians and induces genetic aberrations.
Last few words
At present, bisphenol A is intimately and intricately related to our lifestyle. A study of people in Europe has suggested polycarbonate baby bottles as the most prominent role of exposure for infants, and canned food for adults and teenagers. Actually BPA exposure starts from the mother’s womb. After the baby is born, maternal exposure can continue to affect the infant through transfer of this chemical compound to the infant via breast milk. To cope with bisphenol A toxicity, the European Union and Canada have banned BPA use in baby bottles. In Japan epoxy coating in cans is mostly replaced by PET (Polyethylene Terephthalate) film. Realizing the growing threat of bisphenol compounds, the first world countries all across the world, have already begun to check the indiscriminate use of BPA. In the due course, BPA in some plastic items has been replaced by another phenolic compound BPS (Bisphenol S) to lessen its toxicity. However, this effort becomes futile as BPS is more active than BPA in terms of human exposure. But, sorry to say, in the third world countries like India where bisphenol A is used widely in making various plastic and phenolic products, to common folk and the government are quite unconscious of the emerging threat.