Are more “controls” what is necessary here? The problem wasn’t plastic contamination, it was the presence of stearates. Distinguishing between stearates and microplastics sounds like a classification problem, not a control problem.

There is practically universal recognition among microplastics researchers that contamination is possible and that strong quality controls are needed, and to be transparent and reproducible, they have a habit of documenting their methodology. Many papers and discussions suggest avoiding all plastics as part of the methodology, e.g. “Do’s and don’ts of microplastic research: a comprehensive guide” https://www.oaepublish.com/articles/wecn.2023.61

Another thing to consider is that papers generally compare against baseline/control samples, and overestimating microplastics in baseline samples may lead to a lower ratio of reported microplastics in the test samples, not higher.

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timr 5 hours ago | parent | next [-]

Many papers in this field are missing obvious controls, but you’re correct that controls alone are insufficient to solve this problem.

When you are taking measurements at the detection limit of any molecule that is widespread in the environment, you are going to have a difficult time of distinguishing signal from background. This requires sampling and replication and rigorous application of statistical inference.

> Another thing to consider is that papers generally compare against baseline/control samples,

Right, that’s what a control is.

> and overestimating microplastics in baseline samples may lead to a lower ratio of reported microplastics in the test samples, not higher.

There’s no such thing as “overestimating in baseline samples”, unless you’re just doing a different measurement entirely.

What you’re trying to say is that if there’s a chemical everywhere, the prevalence makes it harder to claim that small measurement differences in the “treatment” arm are significant. This is a feature, not a bug.

	▲	dahart 4 hours ago \| parent [-]
		You’re still bringing up different issues than this article we are commenting on. > There’s no such thing as “overestimating in baseline samples” What do you mean? Contamination and mis-measurement of control samples is a thing that actually happens all the time, and invalidates experiments when discovered. > What you’re trying to say is that if there’s a chemical everywhere, the prevalence makes it harder to claim that small measurement differences in the “treatment” arm are significant. No. What I was trying to say is that if the control is either mis-measured, for example by accidentally counting stearates as microplastics, or contaminated, then the summary outcome may underestimate or understate the prevalence of microplastics in the test sample, even though the measurement over-estimated it.

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njarboe 4 hours ago | parent | prev [-]

Any scientific paper that does not document how things were done (methodologies) is basically worthless in the search for truth.

	▲	dahart 4 hours ago \| parent [-]
		I agree completely. My point is that documenting methodology is standard practice, as is strict quality control, in the microplastics literature. I don’t know what controls are missing according to GP, and we don’t yet have references here to back up that claim. By and large I think researchers are aware of the difficulties measuring this stuff, and doing everything they can to ensure valid science.