To the editor

Despite a report indicating that “modified” polystyrene tubes (Corning; Cambridge, MA) release p-nonyl-phenol1, plasticware continues to be used routinely in the laboratory without testing for estrogenicity. We have conducted a survey of polystyrene dishes from Corning, Iwaki (Tokyo, Japan), Falcon (Newton, MA), Nunc (Rochester, NY), Sumitomo (Tokyo, Japan), and Greiner (Tampa, FL) that confirms certain products confer strong estrogenic potential on the medium kept in them.

Using estrogen receptor-positive MCF-7 cells transiently transfected with 3ERE-GL—a luciferase reporter comprising three estrogen response elements (EREs) ligated into the SV40 promoter of pGL3-promoter Vector (Promega; Madison, WI)—we examined ERE-dependent transcription in medium exposed to 10 different types of plasticware and one type of glassware (see Table 1).

Table 1 Estrogenic potential of different types of plastic labware
Full size table

To carry out our assays, we used polystyrene Corning Costar 24-well dishes (1-ml medium per well), which we previously confirmed had no effect on MCF-7 luciferase activities and therefore had no estrogenic activity. Cells grown in Costar dishes for 24 hours were subsequently exposed to medium that had been stored in polystyrene dishes from the above seven manufacturers either for 2 hours (following 22 hours storage in glass bottles) or for 24 hours.

As shown in Table 1, estrogenic activity of the media was dependent on the time of storage and source of plasticware. ERE-dependent transcription was much higher in Iwaki 10 cm diameter dishes and Corning 10 cm diameter dishes than in other types of plasticware. However, other types of plasticware also demonstrated lower, but detectable, estrogenic potential.

We have repeated these experiments using other types of estrogen-receptor positive cells transfected with 3ERE-GL. We have also confirmed that luciferase expression in MCF-7 cells transfected with a pGL3-promoter vector lacking the three EREs is unchanged under the same conditions. These results demonstrate that many types of polystyrene dishes release estrogenic impurities, a property that should be taken into account when carrying out research using estrogen-responsive cells or studying the cellular effects of this hormone and its analogs.