One winter morning in cold Russia in 1891, the chemist Aleksander Dianin experimented by condensing two ingredients: acetone and organic substances called phenols. One of the products he obtained was bisphenol A (BPA), which, to be exact, combines two molecules of phenol and one of acetone.
Quickly, large multinationals such as Bayer or General Electrics began to manufacture everything from bags to car bodies with it. Since the 1930s, BPA has been the component of the most widely used plastic in products for human consumption: it is incorporated into reusable water and drink bottles, food storage containers, the internal linings of food cans, drink etc
Its versatility is explained, among other things, because mixing BPA with epoxides (molecules with one oxygen atom and two carbon atoms, which react by joining other groups to form polymers) generates new highly malleable, hard, and heat-resistant materials that are easy to manufacture and low production cost.
But at the same time that the use of bisphenols became widespread, their harmful effects on human health began to be revealed. Thus, between 1930 and 1936, the scientist E. C. Dodds and his collaborators published four research articles where they concluded that these compounds act like estrogens, altering the estrous cycle (interval between ovulations) of laboratory rats. This modified their fertility and reproductive capacity.
In 1936, they themselves indicated that bisphenols should continue to be investigated. Despite this, 30 years later, in 1957, Walt Disney built a house made entirely of plastic as the main tourist attraction in his park. It was the heyday of a material that then enjoyed the highest prestige.
Following Dodds' work, we now know that BPA molecules act effectively on estrogen receptors, given their similarity to these hormones. They alter the menstrual cycle and have effects on the endocrine pancreas and other organs.
And in recent years, its effects on the nervous system of numerous species have also been analyzed, from the fruit fly to the human being.
Thus, recent studies reveal a worrying fact: plastic particles, with or without BPA, cross the blood-brain barrier of mammals. This is the name given to the layer of cells that acts as a "door" to the brain, allowing the passage of water and nutrients (glucose, amino acids...) and preventing the entry of harmful agents.
Some of the plastic molecules that reach the barrier become embedded in the membrane, altering its physiology, while others manage to cross it. The latter reach the brain and penetrate the neurons, with serious pathological consequences.
One of the most worrisome effects concerns prenatal development: using mice, it has been discovered that BPA causes a decrease in receptors for the neurotransmitter oxytocin in embryos. This causes alterations in sociability during the life of the animals.
Research with prairie voles shows that BPA also negatively affects neurons that express the hormone vasopressin, producing hyperactivity, anxiety, and inhibition in mate search.
In US citizens, it was also observed that exposure to microplastics during pregnancy has negative effects on behavior and emotional regulation in girls and causes increased anxiety and depression in boys.
And finally, microplastics have been linked in Europe with a reduction of up to five points in intelligence quotient, which leads to problems such as attention deficit and hyperactivity.
And how do these compounds reach our body? The cycle of destruction of plastic begins when it is discarded. In the best of cases, it ends up in a garbage container that will later end up in a landfill. Those of us who live on the coast have in mind the image of seagulls eating remains in the port dump. The majority of their diet consists of plastic fragments.
Plastics also end up in rivers or in the sea. Here they erode, fragmenting into microscopic particles: microplastics, with sizes from 0.1 micrometers (millionth of a meter) to 5 millimeters; and nanoplastics, below 100 nanometers (billionths of a meter). All these tiny fragments are ingested by marine species: from filter feeders at the bottom of the food chain to large fish at the top of the food chain.
In addition to ingesting them, they attach to the gills, invading your respiratory, digestive, filtering, and reproductive systems, and even your brain. Finally, these fish end up on our plate, happily spiced with microplastics invisible to our eyes.
In the last five years, official institutions have dealt head-on with this problem. The European Food Safety Authority (EFSA) has just reached the worrying conclusion that BPA in human food constitutes a health risk: all European citizens ingest more daily BPA than is tolerable.
In order to remedy this, since 2015 the EFSA and the European Union legislate to restrict its consumption in the form of microplastics. A daily intake limit of 4 micrograms per kilo (µg/kg) of body mass was established in early 2015, and already then limits on the amount of BPA in European plastic began. The latest data suggest that thanks to these first measures, it was possible to reduce the intake in the population.
In addition, EFSA launched between 2017 and 2018 a protocol for evaluating the dangers associated with BPA, with the help of a panel of experts. The conclusion of these works is that with a quantity of BPA of only 8.2 nanograms per kilo (ng/kg) of body mass, the immune system presents alterations in the inflammatory response, autoimmunity and lung inflammation.
Therefore, and thanks to the studies carried out since 2015, that first daily intake limit of 4 µg per kg of body mass has been reduced: in 2023, the EFSA has established the amount of 0.2 ng/Kg as a new limit. . However, we are still well above that limit. Microplastics are still too present in what we put in our mouths every day.
This article was originally published on The Conversation.
