A kind reader asks: "Have you heard anything about plastic baby bottles being bad for baby?"
The main concern with plastic baby bottles is that they may leach Bisphenol A, which is what's called an endocrine disrupter or xeno-estrogen. That is, it looks enough like estrogen that proteins in the body bind to it as if it were estrogen, but since it's not the response isn't quite right. This same general principle is kind of part of what makes birth control pills work- disrupting a hormonal feedback loop- except then it's on purpose.
BPA certainly does bad things to rats at both high and low doses. There aren't a lot of decent studies on what it does to humans because a) humans are hard to study; b) reporting of exposure is notoriously ineffective; c) it's unethical to feed people harmful things; and d) it's often very hard to see a weak effect and so researchers would need to, say, take weekly blood samples from a lot of people to get long-term effects.
But in rats, it appears to do a variety of small things- not like instant cancer, just small effects: enlarged prostates, changes in some blood proteins, various hormonal disruptions, effects on the mammary gland, maybe developmental changes. Before you become too distressed, let me remind you that rats aren't people or we wouldn't need to do clinical trials, and nobody's going to keel over immediately from any of these things. On the other hand, bad effects in rats are usually at least a fairly decent gauge of what to avoid. These effects are nothing that's going to do someone instant harm, but nothing that sounds great.
Fortunately, there are many kinds of BPA-free plastic and glass bottles now, which it makes it much easier to avoid in baby bottles.
But. The problem is that this isn't the only place you'll find BPA. It's in some can linings- so that tomato sauce you just bought may have BPA in it. Nalgene bottles are another well-known culprit, but they sell several kinds of BPA-free bottles now. Some are even colors. Maybe your plastic spatula, your plastic-lined travel mug. It's at low levels in some drinking water. It does go from the mother's body into breastmilk, though at low levels; this extraordinarily long and boring review will tell you all about it if you're curious (email me if you want a copy of the PDF).
Nonetheless, take heart! It happens that the safest plastics are numbers 1 and 2, which are also the most recyclable. Here's a good summary of which plastics leach what- the recycling numbers are extremely handy. A quick rundown: 1 and 2 are safe and recyclable; 4 and 5 are safe but less recyclable; avoid 3, 6, and 7. Plastic wrap is PVC (3); I avoid that too.
After writing this I was so alarmed that I went and checked all our plastic goods. Happily, most of it is #2 plastic, along with the ketchup bottle and the juice bottle. Unhappily, much of it is not labeled. And then I threw away the Nalgene bottle.
Seriously, I don't think it's time to get really upset. But it might be best to cut out plastic when possible, and try not to worry about it the rest of the time. And plastic wrap and processed plastic-packaged foods are not so good. But we knew that already, right?