Hypothesis-driven weight of evidence evaluation indicates styrene lacks endocrine disruption potential

Figures & data

Table

Study number in Supplementary Tables 1–6 and text	Study	ToxRTool ccore (maximum score) in vivo: (21) in vitro: (18)	Deficiency/Comment
[1]	Cruzan et al. 2001	21 (21)
[2]	Beliles 1985	21 (21)
[3]	Chamkhia et al. 2006	21 (21)
[4]	Cruzan et al. 2005a	21 (21)
[5]	Cruzan et al. 2005b	21 (21)
[6]	Katakura et al. 2001	18 (21)	The purity or source of the substance not provided; physico-chemical properties not provided.
[7]	Kishi et al. 1992	17 (21)	The purity or source of the substance not provided. The frequency and duration of exposure not well defined; exposure of dams defined as the length of gestation, but that data is provided as mean length of gestation such that length of exposure varied. Does not state that pregnant dams were actually exposed. Authors only state that rats were exposed, they did not specify if the rats were pregnant dams, or if they were pregnant at what number of days of gestation the exposure was started.
[8]	Santini et al. 2008	13 (21)	Purity of the substance was not provided; source or origin of the substance was not provided. Little information concerning exposure details was provided such as hours worked/day, protection used. Not possible to determine doses administered or concentrations in application media given. Sufficient details of the administration scheme was not given; defined as 38 exposed workers; frequency and duration of exposure was not well explained; exposure was indirectly inferred from mean number of years of working. No estimations of vapor concentrations associated with exposure were provided.
[9]	Srivastava et al. 1992a	19 (21)	The purity of the substance was not quantified. The route was insufficiently described as "oral". This could mean any number of things – the way it is written one could assume gavage, but this was not adequately described.
[10]	Srivastava et al. 1992b	15 (21)	Purity of the substance not provided; source or origin of the substance not provided. Since there was no information about the source or purity of the styrene and the route of administration was oral, there is not sufficient evidence that other factors could be influencing the experimental outcomes. Species information limited to albino rats from Industrial Toxicology Research Centre breeding colony. Age of male offspring were known but not dams treated during gestation. Sufficient details of the administration scheme were not given; doses were described as mg/kg bwt but bwts were not given.
[11]	Takao et al. 2000	14 (21)	Purity of the substance was not provided. Although the concentration of styrene in drinking water was provided; the purity of the styrene would affect the overall concentration. Concentration of styrene in drinking water (ad libitum) is provided but volumes of drinking water consumed by subjects is averaged and therefore experimental doses are not known. Sufficient details of administration scheme were not given. The number of test animals was provided in the figures (n = 7 consistently). The dose/animal cannot be determined due to the use of mean ± SEM for the drinking water intake. The use of means ± SEM for exposure is circumspect.
[12]	Murray et al. 1978	21 (21)
[13]	Kishi et al. 1995	18 (21)	The purity or source of the substance was not provided; physico-chemical properties also was not provided. Cannot rule out oral exposure as styrene was introduced into the cage as a vapor.
[14]	Khanna et al. 1991	17 (21)	The purity or source of the substance was not provided; physico-chemical properties not provided. If the purity is not known, then the exposure in oral or inhalation studies cannot be effectively determined. The authors did not specify the particular type of oral route being used, they simply said oral route. The authors needed to be clearer in specifying if the oral route is via gavage, food, water, etc. The authors' study design is inadequate. The authors report and analyze their data with respect to individual animals, when they should actually be performing the analyses and reporting at the level of the litter. The authors are violating the independence assumption required of their statistical methods.
[15]	Cruzan et al. 1998	21 (21)
[16]	Kankaanpää et al. 1980	21 (21)
[17]	Lindbohm et al. 1985	10 (21)	Female workers were enrolled in a case-control study to evaluate spontaneous abortions among women who handled various types of plastics, many of whom handled more than one type of plastic and about one-third of whom may have been exposed to thermal degradation products of plastics. No estimate of styrene exposure was made, and thus, if exposure to styrene occurred, it was likely to have been confounded by exposure to other chemicals, including thermal degradation products of plastics. Exposure information was collected by written or telephone surveys or occupational physicians or occupational nurses; there is a risk of inaccurate or incomplete information, especially if the factory worked with multiple plastic types. Authors identified low statistical power as a weakness of the study that limited interpretations. Due to the use of hospital registries and occupational physician/nurse surveys, it was not possible for the authors to obtain additional confounding factors such as prior obstetric history, alcohol use, tobacco use, and additional potential confounding or explanatory factors.
[18]	Jersey 1978	21 (21)
[19]	Cruzan et al. 1997	21 (21)
[20]	Srivastava et al. 1989	16 (21)	The authors do not specify the purity of styrene, they only state that it is of "the highest purity." The authors do not state if animals were co-housed; also, do not state room conditions. The authors only state that the animals were treated orally – there is no indication of what type of oral exposure was given.
[21]	Date et al. 2002	20 (21)	Strain information was given for all assays except the Hershberger. Housing conditions were not given, including if animals were co-housed or housed individually.
[22]	Ohno et al. 2001	18 (18)	In vitro study

Cruzan G, Cushman JR, Andrews LS, Granville GC, Johnson KA, Bevan C, Hardy CJ, Coombs DW, Mullins PA, Brown WR. 2001. Chronic toxicity/oncogenicity study of styrene in CD-1 mice by inhalation exposure for 104 weeks. J Appl Toxicol. 21(3):185–198.

 PubMed Web of Science ®Google Scholar

Beliles RP, Butala JH, Stack CR, Makris S. 1985. Chronic toxicity and three-generation reproduction study of styrene monomer in the drinking water of rats. Fundam Appl Toxicol. 5(5):855–868.

 PubMedGoogle Scholar

Chamkhia N, Sakly M, Rhouma KB. 2006. Male reproductive impacts of styrene in rat. Toxicol Ind Health. 22(8):349–355.

 PubMed Web of Science ®Google Scholar

Cruzan G, Faber WD, Johnson KA, Roberts LS, Hellwig J, Carney E, Yarrington JT, Stump DG. 2005a. Two generation reproduction study of styrene by inhalation in Crl-CD rats. Birth Defects Res B Dev Reprod Toxicol. 74(3):211–220.

 PubMedGoogle Scholar

Cruzan G, Faber WD, Johnson KA, Roberts LS, Hellwig J, Maurissen J, Beck MJ, Radovsky A, Stump DG. 2005b. Developmental neurotoxicity study of styrene by inhalation in Crl-CD rats. Birth Defects Res B Dev Reprod Toxicol. 74(3):221–232.

 PubMedGoogle Scholar

Katakura Y, Kishi R, Ikeda T, Miyake H. 2001. Effects of prenatal styrene exposure on postnatal development and brain serotonin and catecholamine levels in rats. Environ Res. 85(1):41–47.

 PubMed Web of Science ®Google Scholar

Kishi R, Katakura Y, Ikeda T, Chen BQ, Miyake H. 1992. Neurochemical effects in rats following gestational exposure to styrene. Toxicol Lett. 63(2):141–146.

 PubMed Web of Science ®Google Scholar

Santini F, Mantovani A, Cristaudo A, Rago T, Marsili A, Buselli R, Mignani A, Ceccarini G, Bastillo R, Taddei D, et al. 2008. Thyroid function and exposure to styrene. Thyroid. 18(10):1065–1069.

 PubMed Web of Science ®Google Scholar

Srivastava S, Seth PK, Srivastava SP. 1992b. Biochemical and morphological studies in testes of rat offspring of mothers exposed to styrene during lactation. Pharmacol Toxicol. 70(4):314–316.

 PubMedGoogle Scholar

Srivastava S, Seth PK, Srivastava SP. 1992a. Effect of styrene on testicular enzymes of growing rat. Indian J Exp Biol. 30(5):399–401.

 PubMedGoogle Scholar

Takao T, Nanamiya W, Nazarloo HP, Asaba K, Hashimoto K. 2000. Possible reproductive toxicity of styrene in peripubertal male mice. Endocr J. 47(3):343–347.

 PubMed Web of Science ®Google Scholar

Murray FJ, John JA, Balmer MF, Schwetz BA. 1978. Teratologic evaluation of styrene given to rats and rabbits by inhalation or by gavage. Toxicology. 11(4):335–343.

 PubMed Web of Science ®Google Scholar

Kishi R, Chen BQ, Katakura Y, Ikeda T, Miyake H. 1995. Effect of prenatal exposure to styrene on the neurobehavioral development, activity, motor coordination, and learning behavior of rats. Neurotoxicol Teratol. 17(2):121–130.

 PubMed Web of Science ®Google Scholar

Khanna VK, Husain R, Hanig JP, Seth PK. 1991. Increased neurobehavioral toxicity of styrene in protein-malnourished rats. Neurotoxicol Teratol. 13(2):153–159.

 PubMed Web of Science ®Google Scholar

Cruzan G, Cushman JR, Andrews LS, Granville GC, Johnson KA, Hardy CJ, Coombs DW, Mullins PA, Brown WR. 1998. Chronic toxicity/oncogenicity study of styrene in CD rats by inhalation exposure for 104 weeks. Toxicol Sci. 46(2):266–281.

 PubMed Web of Science ®Google Scholar

Kankaanpää JT, Elovaara E, Hemminki K, Vainio H. 1980. The effect of maternally inhaled styrene on embryonal and foetal development in mice and Chinese hamsters. Acta Pharmacol Toxicol. 47(2):127–129.

 PubMedGoogle Scholar

Lindbohm ML, Hemminki K, Kyyrönen P. 1985. Spontaneous abortions among women employed in the plastics industry. Am J Ind Med. 8(6):579–586.

 PubMed Web of Science ®Google Scholar

Jersey GC, Balmer MF, Quast JF, Park CN, Schuetz DJ, Beyer JE, Olson KJ, McCollister SB, Rampy LW. 1978. Two-year chronic inhalation toxicity and carcinogenicity study on monomeric styrene in rats. Final Report. Dow Chemical Rept MCA NO:STY 1.1-TOX-INH. Midland (MI): Dow Chemical, Health and Environmental Research, Toxicology Research Laboratory.

 Google Scholar

Cruzan G, Cushman JR, Andrews LS, Granville GC, Miller RR, Hardy CJ, Coombs DW, Mullins PA. 1997. Subchronic inhalation studies of styrene in CD rats and CD-1 mice. Fundam Appl Toxicol. 35(2):152–165.

 PubMedGoogle Scholar

Srivastava S, Seth PK, Srivastava SP. 1989. Effect of styrene administration on rat testis. Arch Toxicol. 63(1):43–46.

 PubMed Web of Science ®Google Scholar

Date K, Ohno K, Azuma Y, Hirano S, Kobayashi K, Sakurai T, Nobuhara Y, Yamada T. 2002. Endocrine-disrupting effects of styrene oligomers that migrated from polystyrene containers into food. Food Chem Toxicol. 40(1):65–75.

 PubMed Web of Science ®Google Scholar

Ohno K, Azuma Y, Nakano S, Kobayashi T, Hirano S, Nobuhara Y, Yamada T. 2001. Assessment of styrene oligomers eluted from polystyrene-made food containers for estrogenic effects in in vitro assays. Food Chem Toxicol. 39(12):1233–1241.

 PubMed Web of Science ®Google Scholar