BPA is a synthetic chemical that mimics estrogen, and under certain conditions trace amounts may leach out of the plastics in nalgene. The effective concentration of the said estrogen mimetic is probably at least several orders of magnitude lower than the threshold determined to have adverse health effects in animal studies, as is the frequency of the dose. The BPA that leaches from any plastic container under any circumstances will probably also have an effect on the genes governed by estrogen receptors that is also many orders of magnitude lower than the effect induced by the average meal of tofu, or any other dietary source of phytoestrogens.
If you are concerned enough to replace your Nalgene bottles on account of the risks outlined above, please hang on to them for me as I'd be glad to purchase them from you for $0.50 per bottle. I need to stock up so that I'll have enough to last for a while....
and yet, it's enough to cause mass hysteria, pulling items off of shelves (CYA), and the greedy vultures are circling...