Evaluation of styrene oligomers eluted from polystyrene for estrogenicity in estrogen receptor binding assay, reporter gene assay, and uterotrophic assay.

Styrene dimers (SDs) and styrene trimers (STs) eluted a little from polystyrene have been suspected of having estrogenic activity in the Wingspread Declaration [Our Stolen Futures, 1996] despite the lack of scientific analysis. Therefore, we have studied and reported styrene oligomers to have no endocrine disrupting effects [J. Food Hygienic Soc. Japan 40 (1999) 36; 41 (2000) 109; Yuki Goseikagaka Kyokaishi 57 (1999) 58; Bunseki Kagaku 49 (2000) 493, 857; Food Chem. Toxicol. 39 (2001) 1233; 40 (2002) 129]. However, Ohyama et al. reported that certain styrene oligomers have estrogenic effects in E-SCREEN and estrogen receptor (ER) binding assay [Environ. Health Perspect. 109 (2001) 699]. Recently, several assay systems have been developed, and a few of them can show false positive reactions at the high concentrations to which test compounds are precipitated [J. Health Sci. 48 (2002) 83]. In order to assess the estrogenic effect of SDs and STs in more detail, we examined the accuracy of the binding assay system and tested SDs and STs by three types of ER binding assay. In one ER binding assay, the same method that Ohyama et al. performed, SDs and STs showed a little estrogenic activity at high concentration; they did not dissolve, but this assay system tended to detect false positive effects at high concentration. In contrast, in the other assay systems, SDs and STs did not show any binding affinity to ER. In addition, luciferase reporter gene assay in HeLa cells transfected with ER expression plasmid and reporter plasmid, as a newly developed standard assay, and immature rat uterotrophic assay were conducted. In these tests, styrene oligomers showed no estrogenic activity.