I don't think plastic is safe and avoid it whenever possible, but an argument for its safety is that it has been widely used for a hundred years and we still don't have many direct causal links between plastic and health problems.
If microplastics is a problem, I would expect studies to have shown up linking microplastics to cancer in the elderly, or to dementia, or heart disease, or any of the other very widely spread health issues that could arise after decades of exposure in a population.
I'm not an expert, but wouldn't you need just a scalpel, a microscope and lots of donated tissue samples?
The windows of opportunity would have been narrow to definitively target microplastics as the cause of many diseases where observations of the potential mechanism of action for a morbidity - in this case, probably inflammation or endocrine disruption - could also be caused by other factors which are easier to measure.
This is because plastics became common when a lot of other industrial practices and materials became common in the environment, many of which we know contribute to diseases of modernity.
Microplastic pollution is likely easily confused with other forms of pollutants that were easier to detect historically, and thus care way more about. This would include lead poisoning or carbon monoxide or other chemicals that mimic hormones in the endocrine system.
So why isn't this an argument for disregarding microplastics as being marginal? Because there are microplastics on the larger end which exhibit effects on the endocrine system more definitively than smaller plastics, and these results are easier to report because these plastics are easier to observe.
But with the presence of smaller plastics everywhere, which we would have to know because larger plastics always break down into smaller ones over time, to both understand that they are a common water pollutant yet also observe them in biological tissue requires more precise modalities than historically have been available when microplastic pollution could have started.
It's possible that it might be only "larger" microplastics that have an effect on health, and smaller ones end up being flushed out before they have an effect, or end up not mimicking any hormone and just end up being an chronic inflammatory like pollen would be to those allergic to it.
But that cutoff is quite arbitrary if we rely on just the microplastics that are easy to observe as the only ones that affect our health. A better idea would be to suspect smaller plastics and then gather evidence on their effect on tissues over other pollutants, as the ability to sample them becomes available.
Tupperware was founded in 1946, and the home microwave was invented in 1967. So it has been about 56 years of just that combo. As I said, I agree that plastics cannot be considered safe, but I was presenting a possible argument that others might use.
56 years is kind of an upper bound on microwaving plastics (for the sake of argument, let's focus on that for now), and that's when it started. It means people who were born then and are < 56 years old now might've been exposed to some fraction of (not even nearly the same amount) as much plastic as people born today would be. If we posit that the current exposure levels might cut a few years off the human live... as a layman, naively speaking, can I really expect anybody to have even noticed this in the last 56 years? And given scientific studies like this take years/decades to bear fruit, why would anyone expect this to have been an established fact if it were true?
(I get that this isn't your personal argument; I'm trying to figure out why this argument might seem plausible to other laymen.)
