What are the chances this pot is killing me?

I (sort of) recently was offered my mom's old cookware. I didn't need most of it, but I took her huge and slightly less-huge pots. They're "Club" brand, and the outside is light green.

My problem is that every time I boil water in them, the part that the water has been boiled in turns nearly black, instead of silver like the rest of the interior (see here - ignore the white specks, I took the picture after throwing some salt in there)

I can scrape off all the black stuff, but it happens even if I just boil plain water, so I think it's the actual metal, which seems like a good way to get like... heavy metal poisoning or something, I don't know. I'm not a doctor.

I feel like she said they're aluminum, so at least I'm not cooking with lead pots or something crazy like that, but I'd still like to know if anyone has ever seen this effect before - is it normal for a pot to turn this color when boiling water in it? Should I just toss these? They work really well otherwise.