Originally Posted By: boatman
The older Nalgenes would bounce off rocks /pavement...Frozen solid filled with water,older nalgenes were good to go. I have even used a Nalgene as a wheel chock on a hill for a full size truck.

Honestly, that's exactly the kind of stress that caused the old polycarbonate Nalgene's to leach more and more BPA. Polycarbonate is simply made of long-chains of BPA molecules. It's not an ingredient of polycarbonate--it is polycarbonate. Any stress, like rough handling, stretching from expanding ice inside, etc., damages those chains and they start to unravel. That leads to rapid leaching of BPA into the contents.

I've made this point before but traditional toxicology testing does not seem appropriate to test substances that appear to have biological activity, like hormone disruptors. In traditional toxicology, you give mice more and more of a chemical until you start seeing negative effects. According to those traditional toxicology tests, yeah, there's no way you could ingest as much BPA as used in those tests. But this paradigm assumes BPA is a poison, like mercury or lead.

The other newer paradigm is that a substance can mimic hormonal messengers instead of directly poisoning the body. More recent research tests very, very low concentrations of BPA, levels that your average person has in their blood right now. Because of biological feedback mechanisms in the body, there's a sweet spot of effect--too little or too much and your body ignores it, but at the right dose, BPA can mimic hormones that naturally exist in your body. Hormones are messengers that ramp up or ramp down various functions, so having a fake signal in the body can cause a variety of problems.

For example, it's possible that BPA could be one of the reasons why our daughters are starting puberty at younger and younger ages than ever before, long before they are ready to actually bear children of their own.

I pulled this citation from the FDA website. A 2006 meeting of experts and academics said in their summary of the meeting:

Quote:
...much evidence suggests that these adverse effects are occurring in animals within the range of exposure to BPA of the typical human living in a developed country, where virtually everyone has measurable blood, tissue and urine levels of BPA that exceed the levels produced by doses used in the “low dose” animal experiments.

From: vom Saal FS, Akingbemi BT, Belcher SM et al. Chapel Hill bisphenol A expert panel consensus statement: integration of mechanisms, effects in animals and potential to impact human health at current levels of exposure, Reproductive Toxicology 2007;24:131-8