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Pure PVC is a very brittle plastic so it has many additives.
These used(?) to include phthalates (phytotoxic) as plasticisers, and stabilisers (many toxic) to improve its durability.
I don't like chlorine-based materials on principle (as they are not environment-friendly in production or disposal), but there is a big industry making (useful?) things from them.
Cling-film used to be heavily plasticised PVC, and I can remember that it was being investigated when I started work. Poly-tunnel greenhouses were also reputed to have killed the plants they were protecting!
PVC must be better now (decades later), but vinyl chloride monomer is a carcinogen and it often takes years of suspicion before the effects are catalogued.
With the life-span of cephalopods being short they are not so likely(?) to suffer noticeably from trace chemicals leached from plastics. I would be more afraid of reef tanks, where phthalates could well upset the algal symbiosis in the corals.
You have to keep your eyes and ears open, and do the best you understand.
I have to say our aquarium has been using PVC pipes, valves, siphons etc for the last 30 years! with no effect on the critturs. We do however buy marine grade from marine suppliers, yknow boat builders and the like.