A Blog by Ed Yong

Plastic tubes and pipette tips leach chemicals that botch experiments

Blogging on Peer-Reviewed ResearchThey say that a poor workman blames his tools but according to a new study, laboratory scientists may well have cause to. Reid Macdonald from the University of Alberta has found that some botched experiments may be due to chemicals leaching from the very plastic tubes that scientists use on an everyday basis.

Screw_Top_Microcentrifuge_T.jpgDisposable plasticware like the ubiquitous Eppendorf tubes are a staple of laboratory research, as essential to a biologist as a mixing bowl is to a cook. They are always sterilised before use, which reassures researchers that they can run their experiments free of contamination. But the new study suggests that this sense of security can be a false one.

Macdonald’s group were originally studying a human protein called monoamine oxidase-B (MAO-B),when they realised that it was behaving strangely in their experiments. After poring over other aspects of the experiment, the team realised that it was the equipment that was interfering with their results.

They switched to glass containers and tested solutions that had been used to rinse plastic ones. To their astonishment, they found that pure water which had been stored in plastic tubes for the briefest of moments could then block the activity of MAO-B by up to 40%. The plastic had an even greater effect on another common laboratory solvent called dimethyl sulfoxide (DMSO).

Clearly, one or more chemicals had leached from the tube into the fluids and gone on to affect the protein. Macdonald analysed the liquids’ contents and identified two culprits – a lubricant called oleamide and a disinfectant called DiHEMDA. Both chemicals are deliberately added to plasticware in the manufacturing process, and both of which can block the actions of MAO-B.

The scale of the problem was not limited to plastic tubes. Macdonald also found that the pipette tips that scientists use to transfer liquids from one tube to another can also spike water with chemicals that block MAO-B. And another chemical that leaked into water from plastic plates actually gave the enzyme a boost.

Either way, it’s a problem. It means that standard equipment has the potential to mess around with an experiment’s results to a fairly significant degree.  The scale of the problem isn’t clear, but Eppendorf tubes and pipette tips are two of the most common and essential pieces of equipment used by laboratory scientists. They are manufactured by a few key companies and used by researchers worldwide. Who knows how many results have been skewed by this previously untested effect?

Reference:  G. R. McDonald, A. L. Hudson, S. M. J. Dunn, H. You, G. B. Baker, R. M. Whittal, J. W. Martin, A. Jha, D. E. Edmondson, A. Holt (2008). Bioactive Contaminants Leach from Disposable Laboratory Plasticware Science, 322 (5903), 917-917 DOI: 10.1126/science.1162395

11 thoughts on “Plastic tubes and pipette tips leach chemicals that botch experiments

  1. That’s really interesting – it makes you wonder what other effects might have been missed.
    Can we get a link to or citation of the paper to read ourselves?

  2. Do we have any idea if these compounds are problematic in more than just experiments? I’d tend to suspect that researchers care even more about the proper function of the MAO-B in their nervous systems than that in their experiments.

  3. We found a similar problem in our research about 15 years ago, but it involed plastic conical tubes.
    Here’s a fun/scary experiment you can do for yourself:
    Blank your spectrophotometer against pure water dispensed directly from your Milli-Q into a cuvette. Then dispense the same water into a plastic tube of your choice. Cap and shake vigorously. Now read the UV absorbance, e.g. from 220-300 nm.
    Depending on the tube, you’ll be surprised at how much absorbance you’ll see at low UV wavelengths.

  4. Maybe the biologists should use glass, like us chemists? I’ve long wondered about the wisdom of using techniques borrowed from the biologists – disposable plastic syringes, pippette tips, transfer pipettes, Eppendorf and other plastic centrifuge tubes with organic solvents and reagents. Of course, the effects should be less significant for us than for them.

  5. Wonder how long it’ll take for some whackjob to claim that this means every biological experiment ever done should be discounted, and therefore ID/Creationism was right all along?
    shhhh.. dont tell anyone!

  6. Don’t forget, of course, that even glass can contaminate some experiments (not necessarily biological ones, though). Of course, glass isn’t just a single material, but a class of materials with somewhat similar properties. Most glasses have Sodium in them, which can leach out. Some have a not insignificant amount of Iron. Then, there’s Calcium, Boron (for borosilicate glasses), Silicon, Oxygen, and probably lots of other elements. There’s also the issue of other elements being adsorbed onto the surface of the glass.

  7. Thanks for the citation Ed!
    “Wonder how long it’ll take for some whackjob to claim that this means every biological experiment ever done should be discounted, and therefore ID/Creationism was right all along?”
    I’m sure conservapedia is all over it! Although it might not meet their “need to be able to weasel out of it” standards. ;o)

  8. Your post was very interesting to me because my local collaborator and his colleague at Virginia Tech isolated bisphenol A from what they thought was a soil bacterium when, in fact, it came from the polycarbonate plasticware – they were at first really excited because they though they had found a bacterium that could concentrate BPA. Anyway, it turns out that a similar report came out in the endocrinology literature in 1993. The earlier authors found BPA was released by autoclaving; the current investigators found that autoclaving their polycarbonate did not release BPA but rather required microbial growth. Regardless of the reasons, this is probably the main reason that organic chemists store samples in glass while biologists tend to use various forms of plasticware.
    A great post as usual. Thanks for the heads-up on the Science paper. Hope all is well across the pond!

  9. I have noticed this by LCMS as well. Using disposable plastic transfer pipettes to add solvent to a recently purified small molecule compound introduced a new impurity visible in the UV trace of the final purity assessment. I was able to get the same impurity (retention time and mass spectrum matched) in a blank sample using the same solvents and transfer pipettes. Using glass pipettes did not introduce the new impurity.

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