Generally, there _shouldn't_ be anything toxic in construction dumpsters. Not a lot of home construction deals with anything highly toxic anyway. Plus, if the disposal company finds something in there that shouldn't be there, they will refuse to take it, or levy a fine, or won't work with that contractor anymore.

Conversely, some randos see an open dumpster and think its a great place to chuck their old car batteries and whatnot.

Pressure treated woods scraps are generally thrown in dumpsters and they are toxic if burned. You never burn pressure treated wood.

You just never know though. For instance, it could be thought that there isn't any asbestos in the home being renovated. But maybe there were a couple pieces of drywall or pipe insulation that happened to have asbestos and it wasn't noticed. It happens.

There is also a very good chance that there's lead dust and chips from old paint or pipes that's being thrown in as well. Probably don't want to make charcoal or anything out of that or any new SPF/Doug tossed in there that maybe got some of it on it you don't notice.

Isn't new pressure treated wood safe to burn because they no longer have the nasty chemicals they used to put in them?

There are a range of treatment methods, some of which have fallen out of mass production but none are recommended for burning

Good point. Never ran into anything problematic myself, but we are fairly rural so construction is usually houses with occasional apartments. But definitely be wary of other stuff that may be in with the wood.

As for pressure treated wood, it is pretty obvious what has been treated and what has not, at least in my experience. Not sure if it's the process, or if they intentionally dye it, but treated wood has a strong green tint, though could probably have other colors too depending on the treatment method. But fresh untreated pine has a pretty obvious color.

The old CCA treated stuff got the green from the copper in it. It's hard to tell if the A (arsenic compound) is still in there if it's weathered. Not a good idea to burn scraps from demolished old outdoor stuff.

It turns grey pretty fast. But yes it won’t be pink/white like fresh pine. If you know what you’re doing I’m sure you’re fine.