Labware Contaminants

Science published a study on November 6 conducted by researchers from the University of Alberta in Edmonton, Canada, claiming that chemical compounds leached from disposable plastic consumables tainted experiment data. In an interview with IBO, Dr. Andrew Holt, a researcher involved in the study, made it clear that the results could have wide-ranging implications. “I had quite a number of e-mails from scientists who are either thankful that they might now have found a reason for irreproducible experiments, or [are] expressing a hope that the plastics industry will now work with scientists to come up with a mutually acceptable solution to this problem, rather than deny that any problem exists.”

Dr. Holt and his colleagues were studying the effects of ammonium chloride on the activity of the human enzyme monoamine oxidase B (MAO-B), when data indicated that extremely low levels of solvent were having inhibiting effects on MAO-B, which they knew could not be possible given the large amounts of MAO-B used. Suspecting that chemicals leaching from the microfuge tubes they used could be the cause, the researchers isolated the compounds from the tubes and determined them to be an antibacterial agent and oleamide, both of which are used during the synthesis of polypropylene to enhance properties in plastic. Further experiments showed that both compounds greatly inhibited MAO-B. Later studies of disposable pipette tips and 96-well microplates showed that both types of labware also leached compounds affecting MAO-B inhibition. Dr. Holt made it clear that his group is not the first to publish a report that deals with the effects of compounds leached from disposable plastic labware on experiments, but that the difference in this study was that his group was able to show direct biological effects from a specific compound derived from plastic disposables.

The solution to this problem, as outlined by Dr. Holt, is for companies to provide more information about the contents of their disposable plastic labware. For example, Dr. Holt found that each of the tubes produced by one company varied in the types and levels of interfering compounds they contained. “[We found that] 1.5 mL tubes from one company, manufactured in Germany, had no effect in our experiments, whereas the smaller 0.5 mL tubes from the same series sold by the same company, but manufactured in Italy, showed potent inhibitory effects versus MAO-B,” said Dr. Holt. Further tests showed microfuge tubes used by a colleague inhibited the results on GABA receptors, but not MAO-B. Similarly, the tubes used by the group had no effect on the colleague’s GABA receptor experiment.

Rather than attempting to rid labware of these substances altogether, Dr. Holt suggests a compromise. “Ideally, researchers should be offered a choice of plastics, with the choice relating to the specific processing agents used during manufacturing. If we were offered a choice between tubes and tips containing stearamide, rather than oleamide, and we had determined that stearamide had a negligible effect on our results, then we would choose the former product.”

For the time being, Dr. Holt and his team are cleaning their plastic labware with methanol and water, which takes up to two hours for three hours of use. Although washing can remove contaminants from a plastic’s surface, over time contaminants migrate back out onto its exterior. “We can certainly use small glass vials for preparation of some solutions, but there are not glass alternatives to plastic pipette tips or 96-well microplates,” explained Dr. Holt. “Washing plastics is not an option for researchers working with sterile cell culture disposables. Neither may these researchers use glass, given that it is extremely difficult to ensure that glass is free of all species that might affect cell growth.”

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