Bisphenol S (BPS) is an organic chemical compound belonging to the bisphenol class. It is widely incorporated into consumer products due to its industrial properties, such as being resistant to heat and light. BPS functions as a hardening agent in plastics and resins and a color developer in paper products, leading to its widespread presence in the environment and human population. Human biomonitoring studies have detected BPS in the urine of a large percentage of the population, highlighting the need to understand its potential effects on human health.
The Context: BPS as a Replacement for BPA
The widespread use of Bisphenol S is a direct consequence of public and regulatory concern surrounding Bisphenol A (BPA). Mounting evidence about the health risks associated with BPA, particularly in food packaging, prompted manufacturers to seek alternatives for “BPA-free” labeling. BPS was introduced as a primary substitute, based on the assumption that a structurally similar molecule would be safer.
This market-driven substitution occurred without thorough, long-term safety testing before its broad introduction. The strategy of replacing one bisphenol with another chemically similar compound is now recognized as a regrettable substitution, as BPS may carry comparable toxicological risks.
Common Sources of BPS Exposure
The general population encounters Bisphenol S daily through contact with a variety of consumer goods. One significant source of direct skin exposure is thermal receipt paper, such as cash register or credit card slips. BPS is used as a color developer in these papers and can be present in high concentrations, sometimes up to 22 milligrams per gram.
Another major pathway is through food contact materials, where BPS is used in the protective epoxy-resin linings of metal food and beverage cans. The chemical can leach from the lining into the contents, especially when the food is acidic, salty, or fatty. BPS is also found in numerous plastic items, including polycarbonate plastics used for food containers, reusable drinkware, and certain medical devices.
Furthermore, it is incorporated into synthetic fibers for clothing and textiles, as well as some personal care products. Because BPS is not chemically bound to the polymer matrix in many applications, it readily leaches out, contributing to exposure through ingestion, inhalation of dust, and skin absorption.
Biological Activity and Endocrine Disruption
The primary concern regarding Bisphenol S is its classification as an endocrine-disrupting chemical that interferes with the body’s hormone systems. BPS is structurally similar to natural hormones, allowing it to interact with hormone receptors. The chemical acts as an estrogen mimic, or xenoestrogen, by binding to estrogen receptors, though with a weaker affinity than the body’s own estrogen.
This activity can promote the proliferation of hormone-sensitive cells, such as those found in breast cancer cell lines. BPS can exhibit complex effects on estrogen receptor subtypes, sometimes activating the receptor and at other times inhibiting its activity. This interference is linked to potential impacts on reproductive health, including egg viability and reproductive organ development.
BPS is also recognized as a thyroid hormone disruptor. Thyroid hormones regulate metabolism, growth, and neurological development. The BPS molecule interferes with the thyroid hormone signaling pathway by acting as an antagonist to the thyroid hormone receptor, blocking the natural hormone from attaching.
Disruption of the thyroid system can lead to an increase in serum Thyrotropin (TSH), the pituitary hormone that stimulates the thyroid gland. BPS exposure can impair the thyroid gland structure and interfere with hormone synthesis. Such disruptions are associated with metabolic issues, including insulin resistance and obesity, and adverse effects on neurodevelopment. The ability of BPS to interfere with both estrogen and thyroid hormone systems at low doses suggests wide-ranging health effects, making it a compound of ongoing scientific investigation.
Strategies for Minimizing Exposure
Reducing exposure to Bisphenol S involves making informed decisions about products and handling. A practical step is to limit contact with thermal paper receipts, a concentrated source of the chemical. Consumers should choose digital receipts or forgo them entirely; retail workers who handle receipts frequently may consider wearing gloves.
For food, prioritizing fresh or frozen options over canned goods reduces exposure from can linings. For storage, swapping plastic containers for alternatives made of glass, ceramic, or stainless steel helps lower BPS intake. It is also advisable to avoid microwaving food in plastic containers, as heat accelerates leaching. Finally, consumers should be aware that items labeled “BPA-free” do not guarantee the absence of BPS or other bisphenols.