Last week I did some research on the ABS and PVC ASTM standards.
ABS is not checked for contaminants. There are regulations on the contaminant level for PVC and CPVC. This includes metals.
So if in your ABS batch, the manufacturer used good prime material and they did not have any contamination through the process then you can use it. How do you know?
If it was, let’s say recycled material, or they had a leak of some sort of lubricant, or your batch is the first run after they cleaned their equipment, then your ABS may have contaminants.
There is no way to know, unless you test it for every single contaminant that we care (i.e metals) and at various pH levels.
In terms of power heads and other parts manufactured for aquarium use, they may use a clean ABS, made from prime product and tested.
Surface matters. Compare a 2 sq in surface that is leaching from a union, with maybe 2000 sq in surface leaching from all the tubing.
Leaching may be slow … based on diffusion. It could take weeks, months or years to accumulate contaminants to a dangerous level. At that point you would probably not know what generated your tank regression. Water changes and carbon will help, but some metals can be absorbed and accumalate in rocks, sand, inverts, fish etc.
Let’s ask ourself if we would drink water coming from an ABS system? If we answer NO, then ….
References: ASTM D3965, ASTM D1785, ASTM F441, NSF Std. #61