Location: Sydney, Australia. Found it during bushcare.
The brass barb fitting and the powdery filling suggest some sort of kiln burner to me, but the dark green paint on the outside of the tube looks rather ordinary and not like it has been through high temperatures.
The soft, powdery cemetitious filling has a copper-green tint. Only one end has a hole.
If it were not for the brass barb and coppery fill colour I would assume this is just a bit of structural steel from someone's carport (or similar) that has filled with cement and now been cut to pieces for disposal. But a carport with a barb fitting? WTH?
We find all sorts of garbage in this bushland because it's sandwiched in suburbia. Traditionally it was a dumping ground (mattresses, furniture, asbestos, whole cars) and today still people use it illegally as a dump (mainly building materials and soil). Lots of random materials get deposited by or uncovered by stormwater runoff & floods too. There is no limit to the craziness of what you find here.
You don't. But you also don't know it isn't. And if there was chemical processing involved it could be.
Alright so after looking at the symptoms of arsenic poisoning, I'm not sure how I can tell it apart from getting a combo at Taco Bell with a large fruit punch.