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The Toxic Emissions That Even Electric Vehicles Make
The horrifying reality of TRWP.
Cars make some pretty nasty chemicals. From carbon dioxide and monoxide to nitrous oxide, these vehicles have damaged the planet and our health for over a hundred years. But with the advent of EVs, surely these polluting days are over? Well, as it turns out, not quite. You see, car tyres are a major source of a toxic chemical known as 6PPD, which has killed off entire fish colonies and may even pose a significant threat to your health. What’s even worse, scientists and engineers aren’t sure we can stop this toxic pollution any time soon. So, I will warn you now: this is not a happy article, so read on with caution.
Here is a staggering statistic. 78% of ocean microplastics originate from tyres. You see, as we drive and the tyres age, they get rubbed away, removing tiny flecks of the rubber bit by bit. These microplastics are called Tire-road wear particles or TRWPs, and they are tiny, typically only 100 µm long. Humanity gets through a vast amount of tyres each year, so much so that scientists at Imperial College London estimate that they release 6 million metric tons into the environment annually!
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Now, tyres aren’t made of pure rubber. They have stabilisers and plasticisers mixed within them to make them last longer or work better. One of these additives in particular, 6PPD, which is used to stop them from cracking, can be found in all tyres worldwide. This chemical is what makes TRWPs so toxic.
Studies have found that 6PPD and its oxidised variant 6PPDQ (which forms when 6PPD is exposed to ground-level ozone) are incredibly toxic to several fish species. Two decades ago, there was a mass die-off of coho salmon on the US west coast. Recent research has pinned the cause of this die-off on high levels of 6PPD in the ocean and rivers they swam in. The 6PPD messes with gene expression and some basic cell functionality in these fish. This can lead to haemorrhagic strokes, inflammation, neuronal dysfunction, brain edema, paralysis, and straight-up death. Another study of embryonic rainbow trout gill and liver cells shows that the chemical can stop a cell’s mitochondria from respiring properly, effectively killing the cells individually through asphyxia. Another study found that exposure to roadway run-off (which contains TRWPs) can have a massive effect on juvenile coho salmon’s blood-brain barrier, and that this could be another way 6PPD killed the fish in the early noughts.
Needless to say, this has massive consequences for marine conservation. Particularly as the ocean ecosystems are already on their knees thanks to human impacts. But this raises the question of TRWPs and 6PPD’s effect on humans. After all, we eat plenty of fish, and as road run-off flows through many of our farms, it is fair to assume a lot of our food is inadvertently tainted with this fish-killing chemical.
Well, sadly, there are no direct studies on the human effects of 6PPD. This is because of how hard it is to get a control group, as we are all exposed to these microplastics in the modern world. This means we would have to deliberately dose human subjects with high doses to gleam genuine insights, which is highly immoral and wouldn’t be allowed.
However, new tissue testing techniques are allowing us to find microplastics in tissue samples. This means that through testing on lab mice and studies into lawfully obtained human tissue samples, we can start to piece together a better understanding of how 6PPD and microplastics in general, harm us.
Let’s start with what we have found in Mice. Lab results show that 6PPD and 6PPDQ bioaccumulate in their livers. They also found that, like the fish, it messes with gene expression, affecting parts of the mice’s metabolism pathways and immune system. This leads to hepatotoxicity in the mice, also known as toxic liver disease, which can be fatal. What’s more, mice with high levels of microplastics in their tissue have shown that there are significant cognitive implications. Links have been found between microplastic accumulation and dementia-like symptoms, as well as heightened aggressive behaviour in male mice.
Now, just because it has these effects on mice doesn’t mean it will also affect humans in the same way. As mammals, our biology is similar enough to draw trends but not direct correlations. So, this data, at the very least, suggests that microplastics and 6PPD exposure can have detrimental implications for humans. Sadly, this is where the research ends, as no study has looked into the effect of 6PPD on humans directly in much detail.
However, studies have been done on generic microplastics’ impact on humans by correlating lab results with human tissue samples. These studies found that 80% of human tissue tested contained microplastics, including deep brain tissue. These samples have shown that microplastics are causing oxidative stress, cytotoxicity, neurotoxicity and immune system disruption in humans. Studies have also shown that microplastics containing endocrine-disrupting chemicals can mess with hormone balance in humans. Exposure to these chemicals via microplastics has been linked with reduced fertility, development malformation, immune system suppression and increased aggression in humans. 6PPD is one of these endocrine-disrupting chemicals.
This means that we can say with certainty that the microplastic pollution of tyres is negatively affecting the health of most of humanity.
So, can we solve this? Should we ban 6PPD?
Well, no, we can’t. Tyres without 6PPD are far more fragile and would only last for around 160–1,600 km (99–994 miles) before needing to be changed. Not only would this bankrupt most drivers, but it would also create even more microplastic pollution; even without the 6PPD, it is still dangerous and deadly.
Cyrille Roget, scientific and technical communications director at Michelin, has said that “there is no replacement for 6PPD today that will provide the same benefits to the tyre in terms of safety and have no consequences on the environment.” So, even “sustainable tyres” made from natural rubber and cotton have the same issue.
Now, EVs do produce less tyre wear than combustion cars. They have smoother power delivery and, thanks to their regenerative braking, smoother braking performance too. But they are only marginally better than current combustion cars.
Really, the only solution is to find a biologically neutral form of 6PPD or a brand-new, revolutionary wear-resistant tyre technology. Either way, chemical engineers and scientists have their work cut out trying to solve this problem. In the meantime, there is very little we can do to protect ourselves from this threat. Microplastics have been found everywhere on Earth, even in rain clouds. So it doesn’t really matter where you live, source your food from, or what you drink. This toxic chemical is now perfuse through Earth’s ecosystems, and you can’t escape it.
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