When heated -- especially in the context of moist food -- plastic has the most estrogenating material released. In this context, I would never consider it safe. Definitely get a stainless steamer as suggested.

When storing dry goods temporarily - e.g. some nuts in a ziploc bag -- I usually don't worry much at all. I do carry my work-lunch in a glass/pyrex container with a plastic lid, but I do not reheat the food with the lid on.

Plastics are everywhere - minimize exposure when you can, but don't fret when you cannot.

I stay away from plastic that will be heated, plastic water bottles that may have languished in a hot warehouse before getting to me, nonstick pans, and silicon bakeware/mats. There are glass or plastic or metal or parchment alternatives for almost every use of 'durable' plastics.

That said, I buy milk in plastic jugs, will use ziplocs or plastic wrap for short term storage, and I would not be above condom use if needed. Approaching zero exposure in the current world we live in is exponentially difficult; just minimize everywhere it's feasible for you.

It's not just BPA, just about all plastics contain estrogenlike compound. But rather than ramble on, here's Chris Kresser's article on it that's better than anything I could write.

http://chriskresser.com/how-plastic-food-containers-could-be-making-you-fat-infertile-and-sick

Situations to minimize exposure to BPA/plastic components: Don't heat plastic, store acidic food in plastic, or high-fat food in plastic that is NOT BPA free. Check the bottom of any new containers, it will brag that it's BPA free if it is. Check if your brand of canned foods is BPA free- this is where it is really hairy. Coconut milk, tomatoes, and other acidic vegetables/fruits are the ones you want to be most careful that the cans are BPA free.

For your steamer, the stainless steal one are pretty cheap. If you have an old plastic electric kettle, consider updating to a stainless steal one. Consider replacing old plastic containers (especially ones that have cycled through microwaves over the years) with BPA free plastic, metal, or glass. Look into BPA free brands of canned coconut milk, tomatoes etc; you can order them off amazon if there's none in your local area.

Plastisizers have limited volatility, so you're not going to have problems with vapors. They're lipophilic molecules, so water/steam shouldn't extract high amounts either. I'd say the risk is very minimal.

Good question, I'd flip it around though and ask in what context is plastic safe?

Just having more decorations in one's home has been linked to PCOS, and that doesn't even involve food preparation.

"...from Nanjing Medical University in China evaluated 108 women with PCOS and 108 women free of the disorder.

They found that risk factors for PCOS were: occupation, education, disposable plastic cups for drinking, cooking oil fumes and indoor decoration. The strongest risks factors were disposable plastic cups for drinking, cooking oil fumes and indoor decoration."

http://www.ovarian-cysts-pcos.com/pcos-news136.html#sec3

I asked myself the same question. What needs to be figured out is the type of plasticizer (phthalate or not) found both on the plastic tray and on the bottom of the steamer -- usually steamers come in with a sticky-free shell. I believe this sticky-free matter is usually plasticizer based.

It's one thing to know which type of plasticizer is found there (some types of phthalates are worse or more prone to leaking than others), it's another to determine the amount which leaks into food. Steaming is otherwise healthy, I'm inclined to believe this outweighs the plastic issue. However it is true that heat promotes plastic leaking, so it's a valid question to ask for a steamer.

Go with stainless:

Secura 3-Tier Stainless Steel Food Steamer, w/ Steam360 technology

http://www.amazon.com/gp/product/B004MKG8H8/ref=as_li_ss_tl?ie=UTF8&tag=debralynndadd&linkCode=as2&camp=217145&creative=399373&creativeASIN=B004MKG8H8

my dehydrator is plastic... are there any alternatives?

I cringe when I read the phrase "microwave safe" on labels for various plastics. Safe, by what standards, according to whom, based on what research? I don't doubt that such claims often are "tested" but who oversees veracity and validity of claims put forward by companies with a proprietary interest in convincing consumers "our stuff is safe."