Three small fish species, medaka (Oryzias latipes), fathead minnow (Pimephales promelas), and zebrafish (Danio rerio), were exposed to an estrogen, 17 beta-estradiol (E2), and an androgen, 17 beta-trenbolone (TB), for 21 d under flow-through conditions to compare the susceptibility among these three small fish species to the substances. Effects on gross morphology, including secondary sex characteristics and gonadosomatic index, as well as on blood or liver vitellogenin (VTG) levels were assessed. In E2 exposures, significant increases in estrogenic activity were observed in both sexes of all three fish species. The lowest-observed-effect concentrations (LOECs) of E2 for VTG induction in males of medaka, fathead minnow, and zebrafish were less than or equal to 8.94, 28.6, and 85.9 ng/L, respectively. In TB exposures, we observed masculinization of secondary sex characteristics in females as a result of the androgenic activity of TB in medaka with a LOEC of 365 ng/L and in fathead minnow with a LOEC of 401 ng/ L. We also found VTG reduction in females of all three fish species. These results suggest that the susceptibility of medaka to estrogenic chemicals may be higher than those of fathead minnow and zebrafish and that the susceptibility of medaka to androgenic chemicals may be almost equal to that of fathead minnow in the 21-d fish assay.

HighlightsWe evaluated the genotoxicity of styrene oligomers extracted from polystyrene intended for use in contact with food.Compared with 50% ethanol, acetone extracted a far greater amount of styrene dimers and trimers from polystyrene.Ames tests and an in vitro chromosomal aberration test were negative.The risk of the genotoxicity of styrene oligomers migrated from polystyrene food packaging into food is likely very low.

Background Conflicting results between bacterial mutagenicity tests (the Ames test) and mammalian carcinogenicity tests might be due to species differences in metabolism, genome structure, and DNA repair systems. Mutagenicity assays using human cells are thought to be an advantage as follow-up studies for positive results in Ames tests. In this collaborative study, a thymidine kinase gene mutation study (TK6 assay) using human lymphoblastoid TK6 cells, established in OECD TG490, was used to examine 10 chemicals that have conflicting results in mutagenicity studies (a positive Ames test and a negative result in rodent carcinogenicity studies). Results Two of 10 test substances were negative in the overall judgment (20% effective as a follow-up test). Three of these eight positive substances were negative after the short-term treatment and positive after the 24 h treatment, despite identical treatment conditions without S9. A toxicoproteomic analysis of TK6 cells treated with 4-nitroanthranilic acid was thus used to aid the interpretation of the test results. This analysis using differentially expressed proteins after the 24 h treatment indicated that in vitro specific oxidative stress is involved in false positive response in the TK6 assay. Conclusions The usefulness of the TK6 assay, by current methods that have not been combined with new technologies such as proteomics, was found to be limited as a follow-up test, although it still may help to reduce some false positive results (20%) in Ames tests. Thus, the combination analysis with toxicoproteomics may be useful for interpreting false positive results raised by 24 h specific reactions in the assay, resulting in the more reduction (> 20%) of false positives in Ames test.