If you really want to know what it is, I suggest hiring someone who actually knows how to collect samples. Look for an EPA certified Lead Dust Sampling Technician. Not suggesting that you have lead, rather that you need a collection protocol more reliable than picking bits out of your vacuum.
Marc, on the left is a channel drain. It has metal edging on it to make grouting cleaner and easier. The tiles are cut so the woodgrain pattern continues across the drain.
On the right is a metal edge at the end of the shower pan. A large sheet of glass will be sitting there.
I don't have a picture of the pan before I tiled. I'll post a pic after its grouted.
It's confetti made from recycled newspapers and cereal boxes. The boric acid treatment is a fire retardant and makes it pest resistant. Without the treatment, it's kindling and pet bedding.
My house is 100 years older than I am. It has a dirt floor crawl without a vapor barrier (it's too short to roll one out. I've tried). This time of year a small brook trickles through the basement. You would have to run a control sample to rule out the mold I carry into your test environment.
Nothing in the code says that the header has to be at the top of the window. There is no prohibition of placing it in the platform assembly. In fact, the TJI manuals typically detail several options for doing exactly that.
Joist hangers. By moving the header into the platform you create room for installation. Especially important if you're going to rely on inefficient fiberglass.