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Why plastic isn't always fantastic

Experiment-ruining chemicals leach from plastic lab equipment.

Chemicals leaching out of plastic pipette tips and tubes could be affecting experiments Credit: Punchstock

Thousands of scientists could be unwittingly ruining their own experiments merely by using standard plastic lab equipment, according to a new study.

Andrew Holt, a researcher at the University of Alberta in Edmonton, Canada, was looking at how drugs affected the human enzyme monoamine oxidase B when he noticed that the drugs seemed to be inhibiting enzyme activity at much lower concentrations than they should.

Holt washed out his equipment with water, methanol or dimethylsulphoxide (DMSO), then analysed what chemicals had leached into the solvents using mass spectrometry. Reporting in Science1, Holt and his colleagues show that the plastic tubes they were using were leaching the disinfectant di(2-hydroxyethyl)methyldodecylammonium (DiHEMDA) into water and the lubricant oleamide into methanol and DMSO.

"The compounds that leached out of the plastic were remarkably potent inhibitors," Holt told Nature News. "We were getting variability caused by these leachates that could completely mask the effects of the drugs."

Although some tubes leached almost no contaminants, even brief exposure to some tubes gave concentrations of around 40–50 parts per million of oleamide in DMSO and around 200–350 parts per million DiHEMDA in water.

Holt's colleague Susan Dunn works on a neurotransmitter called γ-aminobutyric acid (GABA). Further work in her laboratory demonstrated that her equipment was leaching compounds that affected binding to GABA receptors. Another researcher in the department found a similar problem, suggesting that leachates from plastic pipette tips, tubes and micro-plates could be affecting the work of thousands of researchers worldwide.

"I suspect quite a large number of researchers are going to have their results affected," says Holt. These contaminants are used during plastics manufacture. "People in any big science department will say that they don't trust plastic in some experiments," says Holt. But the identity of the compounds responsible has never been determined before.

Go glass

"It doesn't surprise me," says Rona Ramsay, an enzymologist at the University of St Andrews, UK, who has worked extensively with monoamine oxidase B and has noticed the problem before. "I talked to one of the authors [of this paper] at a conference and I reassured him he wasn't going crazy."

But Ramsay says that people who do not pay attention to the enzyme kinetics as carefully as Holt did may run into trouble. She has long used an work-around for the problem: "I always use glass," she says.

However, plastic pipette tips and microplates are a vital part of the set-up in the Alberta laboratories. Researchers there have to do a painstaking rinse-through of all equipment with methanol and very pure water immediately before any experiments. But "in some experiments this can double the amount of time an experiment takes", says Holt.

Eppendorf, a manufacturer of some of the plastic products in question, says that "so far, we have not experienced any product problems with our customers due to the substances mentioned by McDonald et al. Principally, all highly sensitive assays may be influenced by the surface properties of vessels, made out of any kind of material. For scientists this is common knowledge."

Credit: Punchstock

References

  1. McDonald, G. et al. Science 322, 917 (2008).

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Department of Pharmacology, University of Alberta

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Cressey, D. Why plastic isn't always fantastic. Nature (2008). https://doi.org/10.1038/news.2008.1212

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  • DOI: https://doi.org/10.1038/news.2008.1212

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