Plastic bottles

Researchers had hoped the brain could deal with bisphenols such as BPA and BPS. They were wrong

Ahad Sanwari

Platicizers, the stuff that makes plastic so soft and pliable, are released in large quantities when things breaks down. Researchers recently tested their effects on vertebrate brain neurons to see if the brain has a problem with it. Short answer: Oh yes!

Elisabeth Schirmer, Stefan Schuster, and Peter Machnik of the University of Bayreuth in Germany studied the effects on the brain of the most frequently used plasticizers, bisphenol A (aka BPA, or 4,4′-Isopropylidenediphenol), and bisphenol S (BPS, or 4,4′-sulfonyldiphenol).

Machnik pointed out that BPA had already been shown to damage the developing brain.

“In some economic areas, it has in consequence been banned from toys and baby products,” he told Truly Curious. And so the industry came up with a replacement: BPS.

The chemical structures of BPA and BPS
3D structures of BPA (above) and BPS (below). The atoms depicted are carbon (gray), oxygen (red), sulfur (yellow) and hydrogen (white). Images adapted from PubChem, at the NIH National Library of Medicine

A solution as bad as the problem

Manchik said there was no evidence that BPS was safer as an alternative when it came to brain function. Besides, research shows that BPS is not great for cardiac health, the production and operation of genes and hormones, pregnancy, early development, skeletal health, weight control and some other things that just may have missed our plastic-addled minds. Besides cancer

And, oh, there is also evidence that it is not too good for brain health. It seems to be particularly partial to the hypothalamus. That is a wee bit important because it helps regulate body temperature, eating, drinking, sexual drives, sleep cycles, etc.

So the Bayreuth team studied “the impact of both BPA and its main substitute, BPS, on the mature vertebrate brain.” Manchik said they hoped the brain’s corrective mechanisms could somehow “potentially compensate for any effects bisphenols might have.”

The researchers worked with fish – vertebrates like themselves and us. Which makes sense, given that much plastic heads out to sea, and BPA, at least, degrades slower in sea water.

The route that BPA and BPS take during degradation
As plastic degrades, BPA and BPS are released into the environment and are then able to pass the blood–brain barrier (BBB). BPA, the most widely used plasticizer, is released at millions of tons per year and has devastating effects on health. Its substitute, BPS, also appears problematic. Pic courtesy Communications Biology. CC BY 4.0

The experiment

First, to test short-term effects of bisphenols, for about an hour the researchers exposed groups of fish to BPA, BPS, or the solvent the bisphenols had been dissolved in.

They exposed six other groups of adult goldfish (Carassius auratus) to different doses of BPA, BPS, or so for 30 days. One group, the control group, got no exposure to the bisphenols, only to the solvent the bisphenols had been dissolved in. The others received BPA or BPS in doses of 10 micrograms per liter or 1 milligram per liter. The last set got 1 milligram per liter of ethinyl estradiol, a synthetic form of estrogen. Given that BPA and BPS resemble estrogen in some respects, the team could compare the effects with the synthetic estrogen.

“We used intracellular in vivo recordings in a central command neuron for that, the Mauthner neuron of goldfish,” says Machnik.

That calls for some unpackaging. The researchers were testing the nerve activity in a live cell, the Mauthner neuron, which are big and easily identifiable and easily located in the medulla oblongata. It is usually responsible for triggering the escape response in the face of predators.

The kind of goldfish used in the experiment
Carassius auratus, the kind of goldfish used in the experiment. Pic courtesy PxFuel

The results

After a month of exposure to BPA, the cells start experiencing neuronal backfiring. That is when the flow of information in the form of chemical impulses from one neuron to the next being effectively reversed where they meet. This affects the membrane of the first cell enough to make it send another signal. This delays overall information flow to the spinal cord and brain.

The damage is slow, but starts expanding, even affecting processing of sights and sounds. What’s worse is the implication that this damage could take place in the mature adult brain, not just the brains of vulnerable fry and fingerlings.

The disastrous effects go beyond neuronal backfiring.

Both BPA and BPS had clear effects on nerve function on the fish exposed for a month.

The groups exposed for just an hour to either bisphenol showed no effects.

Mauthner cell image
An image of a damaged Mauthner cell during recovery. Image adapted from Communications Biology. CC BY 4.0


“The impact on central processing of sensory information is alarming,” Machnik says. “They offset the delicate balance between excitation and inhibition in the brain.” As the paper points out, this is the basis of several neurological disorders.

According to Machnik, “that not even the mature brain can [correct for] the strong effects of bisphenols on the vertebrate central nervous system should definitely make us rethink the use of bisphenols in general.”

The researcher stresses the urgent need to act.

“Our findings call for new approaches to speed up the development and efficient pre-testing of alternative plastic additives,” he says. “The assay we describe here could … provide comprehensive information on the effects of anthropogenic substances on the mature brain.”

There are two ways to address the problem he raised. One is to find a new, plasticizer that is nothing like BPA and BPS, and perhaps decomposes faster while maintaining the integrity of the product it is in.

The second option, one Machnik and his team enthusiastically endorse, is a better system – a scientifically backed one – to test future plasticizers for potential side effects early on in the process.

As far as BPA and BPS go, the team is quite certain: they should be history.

Ahad Sanwari, a recent graduate of the NYU School of Journalism, is a prolific feature writer

Click here for the original paper in “Communications Biology

‘It’s raining plastic’

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