Many plastic products contain bisphenols as plasticizers. Bisphenol A (BPA) in particular is already known to pose health risks, especially since it interferes with the human endocrine system. Bisphenol S (BPS) was previously considered to be better tolerated. However, a study on goldfish now shows that both bisphenols have serious effects on signal transmission in the brain. Even at concentrations that can realistically occur in the environment, the function of vital nerve cells in the fish’s brain was impaired. The researchers assume that the results can be transferred to humans.
Bisphenols are used as plasticizers in a large number of plastic products – from food packaging and drinking bottles to toys and baby pacifiers. The plasticizer bisphenol A (BPA) is particularly widespread. Eight million tons are produced worldwide every year, 100 tons are released into the environment every year. They pollute drinking water and can even be found in breast milk. Several studies have already shown that BPA interferes with the human hormonal balance through a structural similarity to estrogen, can cause developmental disorders and is associated with numerous diseases. This is why BPA was banned across the EU in baby pacifiers in 2011. Bisphenol S (BPS), which is considered to be less harmful, is often used as a substitute. In the meantime, however, there are indications that BPS is also not without its problems.
Investigations on the fish brain
A team led by Elisabeth Schirmer from the University of Bayreuth has now shown in goldfish that both bisphenols have a harmful effect on the adult brain. “We were surprised how many vital brain functions in fish are weakened by the plasticizers used in numerous branches of industry,” says Schirmer. “As we were able to show, the damage does not occur immediately. But when the brain cells are exposed to low levels of BPA or BPS for a month, the damage is obvious. “
For the study, the researchers focused on the so-called Mauthner cells in the goldfish’s brain. These large, paired nerve cells are responsible for the fish’s escape reaction. This is where all the sensory stimuli come together and are processed quickly and in a coordinated manner. Only the precise coordination of the incoming signals enables the fish to flee from predators. The Mauthner cells are known not only for their size, which makes them easily accessible for examinations, but also for the fact that they can regenerate to a certain extent and compensate for damage.
Communication of the nerve cells disturbed
Schirmer and colleagues exposed different groups of goldfish to different concentrations of BPA and BPS for a month. For the examination, they anesthetized the living fish, excited the Mauthner cells in their brain with electrical, acoustic and visual stimuli, and measured the reactions. It was found that even at a concentration of just ten micrograms per liter, which can certainly occur in the environment, both BPA and BPS influenced the transmission of action potentials in the nerve cells. The processing of acoustic and visual stimuli was also impaired. While acoustic signals produced an excessive neural response, the effect of visual stimuli was weakened.
Apparently the bisphenols disturbed the balance of inhibitory and excitatory signals in the communication between the nerve cells. “It is known that numerous disorders in the nervous system of vertebrates are triggered by the fact that excitation signals and inhibition signals are not or only inadequately coordinated. It is all the more worrying that the plasticizers BPA and BPS significantly impair this coordination, ”explains Schirmer’s colleague Peter Machnik. According to the researchers, these effects are at least partly due to the fact that the bisphenols have a structure similar to that of estrogen. Schirmer and colleagues showed this in another group of fish that they treated with an estrogen instead of BPA or BPS. While the effects were not entirely the same, they were largely similar.
Help with the development of new plasticizers
While it was previously mainly known that bisphenols can disrupt the development of organisms, the current study also shows serious effects on the adult brain. “The knowledge gained through studies on fish brains justify the assessment that BPA and BPS can also seriously damage the brains of adults,” says Machnik. “Against this background, it is imperative that science and industry develop new plasticizers that can replace these bisphenols and are harmless to health.”
Studies on goldfish could also help here. It is particularly important to quickly test potential candidates for possible environmental and health risks and, if necessary, to sort them out. “The tests we used are particularly efficient and can quickly check the effects on neural functions. Together with similarly sensitive test procedures, they could show us the way to the urgently needed next-generation plasticizers, ”said the researchers.
Source: University of Bayreuth, specialist article: Communications Biology, doi: 10.1038 / s42003-021-01966-w