I should have been more specific and said that there are some indications that glyphosate may cause disruption in hormone signalling, here are a few references:
‘Rana pipiens tadpoles chronically exposed to environmentally relevant concentrations of POEA or glyphosate formulations containing POEA showed decreased snout-vent length at metamorphosis and increased time to metamorphosis, tail damage, and gonadal abnormalities. These effects may be caused, in some part, by disruption of hormone signaling, because thyroid hormone receptor beta mRNA transcript levels were elevated by exposure to formulations containing glyphosate and POEA. Taken together, the data suggest that surfactant composition must be considered in the evaluation of toxicity of glyphosate-based herbicides. (see Toxicity of glyphosate-based pesticides to four North American frog species. Howe CM, Berrill M, Pauli BD, Helbing CC, Werry K, Veldhoen N.
http://www.ncbi.nlm.nih.gov/pubmed/15352482)
There is an interview during a meeting in Denmark with Prof. Gilles-Eric Seralini, where he says that ‘My team has noticed that Roundup disrupts hormones (chemical messengers) which are modulating the oestrogen synthesis. Oestrogens are known as female hormones, but today we know that they are important for bone growth and testicular function at very low doses. So a modulation of oestrogen synthesis could account for sperm decline, increase in cancers and sexual malformations. So we have to be careful with the hormonal effects of GM crops and the associated herbicides.’ see
http://www.ecochem.com/ENN_glyphosate(2).htmlWalsh, L.P. 2000. Roundup inhibits steroidogenesis by disrupting steroidogenic acute regulatory (StAR) protein expression. Environ. Health Persp. 108:769-776. is another study on effects on hormones. These scientists at Texas Tech University studied the effect of a glyphosate containing herbicide on hormone production. They looked at hormone production by Leydig cells, located in the testes, which play a crucial role in male reproductive function. The scientists showed that exposure to a Roundup herbicide reduced sex hormone production in these cells by 94 percent.
R. Hokanson et al. in their study: Alteration of estrogen-regulated gene expression in human cells induced by the agricultural and horticultural herbicide glyphosate (Human and Experimental Ecology (2007) 26,747—752 wrote: ‘Gene expression is altered in mammalian cells (MCF-7 cells), by exposure to a variety of chemicals that mimic steroid hormones or interact with endocrine receptors or their co-factors. Among those populations chronically exposed to these endocrine disruptive chemicals are persons, and their families, who are employed in agriculture or horticulture, or who use agricultural/horticultural chemicals. Among the chemicals most commonly used, both commercially and in the home, is the herbicide glyphosate. Although glyphosate is commonly considered to be relatively non-toxic, we utilized in vitro DNA microarray analysis of this chemical to evaluate its capacity to alter the expression of a variety of genes in human cells.’
It is probably not glyphosate alone, but the cocktail of this and other factors that may constiute a threat, among them modified insecticidal Bt toxins that are produced by GM plants which have developed resistance to glyphosate, ref. Mesnage R, Clair E, Gress S, Then C, Székács A, Séralini GE. Cytotoxicity on human cells of Cry1Ab and Cry1Ac Bt insecticidal toxins alone or with a glyphosate-based herbicide. J Appl Toxicol. 2012 Feb 15. doi: 10.1002/jat.2712. From the abstract:
‘ In these results, we argue that modified Bt toxins are not inert on nontarget human cells, and that they can present combined side-effects with other residues of pesticides specific to GM plants.’
In a study by Céline Gasniera, et al: Glyphosate-based herbicides are toxic and endocrine disruptors in human cell lines. Toxicology Volume 262, Issue 3, 21 August 2009, Pages 184–191,
http://www.sciencedirect.com/science/article/pii/S0300483X09003047) they say that it is probably not glyphosate that is the most toxic component in various Roundup formulations, but that other ingredients in the formulations disrupt hormone function more efficiently than purified glyphosate. The findings show that the formulations act against the hormones to produce anti-estrogenic and anti-androgenic effects. There is a synopsis of this article here:
http://www.environmentalhealthnews.org/ehs/newscience/roundup-mix-more-toxic-to-liver-cells-than-glyphosate/