This was in mice that were given up to 1000 mg/L of microplastics in their drinking water. If you have this level of contamination, you probably should stop whatever it is you are doing anyways, disregarding your testicles. But even then, there is no evidence for this in humans. Research shows that most microplastics simply passes through your digestive system unhindered.

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dijit 3 hours ago | parent [-]

Yeah, typically we test adverse effects in mice before doing trials on larger animals.

That we haven't observed such extreme behaviour in a scientific way in humans doesn't mean it isn't there, it's just that we haven't yet scientifically observed anything. That there is some evidence in favour of it having adverse effects somewhat defeats the idea that it's "provably non-harmful", which is your current stance.

It might be interesting; instead of downplaying the harm, to see if we can observe any patterns that fit with these findings over the course of human history with the introduction of microplastics...

and if we were to do that, we'd find some interesting correlation, even if it's not provably causation yet.

https://www.healio.com/news/endocrinology/20120325/generatio...

We also know that plastics are a source of hormone disrupting chemicals; https://health.clevelandclinic.org/how-environmental-toxins-...

Bury your head I guess? Just make sure it's not a polyester pillowcase.

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sigmoid10 3 hours ago | parent [-]

Sorry, I still subscribe to science and not speculation. But I guess I am increasingly alone with that idea on HN. And to be clear if someone points out a rigorous causal link, I'd be onboard immediately. But this purely speculative fear mongering based on random scientific observations targeted at non-scientists is similar to what you see in the homeopathy and energeticism circles. Except noone here would believe that 5G makes you sick, because techies know at least this kind of science a little bit.

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dijit 3 hours ago | parent [-]

The science disagrees with your hypothesis that "provably, nothing is the matter".

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sigmoid10 3 hours ago | parent [-]

Then please link to it. I'm still waiting for a causal health issue meta analysis that disagrees with me. Shouldn't be hard, if "the science" as you call it has come to a consensus. But I have only seen wild speculation so far like the one linked here.

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dijit 2 hours ago | parent [-]

Sure. Here's a few:

- Microplastics found in 76% of human semen samples, with PET-exposed men showing reduced sperm motility: https://pmc.ncbi.nlm.nih.gov/articles/PMC12299061/

- Multi-site study across China (113 men), PTFE microplastics linked to sperm dysfunction (published in eBioMedicine/Lancet): https://www.thelancet.com/journals/ebiom/article/PIIS2352-39...

- Microplastics found in every human testicle sampled, at 3x the concentration of dogs, with PVC correlating to lower sperm count in canines: https://pubmed.ncbi.nlm.nih.gov/36948312/

- In-vitro exposure of human semen to polystyrene MPs showed time-dependent decline in motility and increased DNA fragmentation: https://www.mdpi.com/2305-6304/13/7/605

The mouse study I linked earlier isn't the whole picture; it's one piece. The "no human evidence" line was maybe defensible in 2022. It isn't anymore.

Also, re: "1000 mg/L is unrealistic".. the study used two doses, 100 μg/L and 1000 μg/L. Raw surface water in Amsterdam has been measured at ~50 μg/L. The lower experimental dose is well within an order of magnitude of real-world contamination. That's how dose-response science works.

Comparing this to homeopathy is… a choice.

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sigmoid10 2 hours ago | parent [-]

You'll excuse me if I only explain the first one, since the others seem redundant (not to say suspiciously redundant if you look at the authors). And none of this is a meta review like I asked, but I'll let it slide this time.

First:

>no significant association was found between MP exposure and sperm concentration or total sperm count

Second: N=34

Third (if second didn't give it away): The one effect they did find sits at p=0.056. That means one in 18 random studies will find that effect just because of probability statistics. And as you have nicely pointed out, there are maaaany studies like this out there. You just don't find all the null results if you go into research with your mindset. But that is exactly what differentiates a scientist looking for truth from a hobbyist trying to argue on the internet.

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dijit 2 hours ago | parent [-]

You asked for a meta-analysis. Here's one: 39 studies, published in the Journal of Hazardous Materials:

https://www.sciencedirect.com/science/article/abs/pii/S03043...

It found microplastics caused a decrease of 5.99 million/mL in sperm concentration, 14.62% in sperm motility, 23.56% in sperm viability, and a 10.65% increase in sperm abnormality rate. (I copied and pasted these values directly from the source).

You said you'd be "onboard immediately" if someone showed you a rigorous causal link. This is a meta-analysis with an adverse outcome pathway mapping the causal chain from molecular initiating event (ROS) through to tissue-level damage. That's about as rigorous as it gets before human clinical trials, which (for obvious ethical reasons) nobody is going to run.

As for the p=0.056 critique: you picked the weakest single data point from one of four links and declared victory (scientific!). The in-vitro study I linked exposed actual human semen to microplastics under controlled conditions and observed time-dependent decline in motility and increased DNA fragmentation. That's not a simple correlation, it's a direct causal experiment on human tissue. You didn't address it.

The goalposts have moved from "show me evidence" to "show me a meta-review" to "well not THAT meta-review." At some point you have to engage with what the research actually says rather than with what you'd like it to say.

	▲	sigmoid10 2 hours ago \| parent [-]
		Doesn't this one directly contradict the other one you linked? What is it now? How is my sperm in danger!? Please Mr. Googlescienceman! Oh god! I'm so confused! I can't take it anymore. Please just tell me what brand of air filter and plastic free clothes I need to buy!! Perhaps I should ask the all mighty google AI overview... Edit: Oh - lol XD. It literally just told me the science has found no causal link for microplastics harm. Hm. I guess you are just better at researching random studies than us mortals with stupid science degrees and hyped summary machines.